lhe situation of common wheat rusts in the Southern Cone of Americaand perspectives for control

Silvia CermaacutenAJ Amarilis BarcellosB Marcia Chavesc Mohan KohlD Pablo CamposE

and Lidia de ViedmaF

ACorresponding author II IA La Estanzuela CC 31173 Colonia CP 70000 UruguayEmail sgermaniniaorguy

BOR Melhoramento de Sementes Ltda Rua Joatildeo Ballisti 71 Passo Fundo CP 99050-380 RS BrazilcEMBRAPA Trigo Rodovia BR 285 km 174 Passo Func1o CP 99001-170 RS BrazilDCAPECO Av Brasilia 840 Asuncioacuten ParaguayEINTA Bordenave CC 44 Bordenave CP 8187 ArgentinaFvAGDIACRIA Ruta VI km 16 Capital Miranc1a Itapuacutea Paraguay

Abstlact Approximately 9 million ha 01 wheat (TriliCllIll aeslivum anel T dUllIJl) is sown in the Soulhern Cone 01Imerica (Argentina Brazil Chile Paraguay anel Uruguay) Two rust epielellliological zones separateel by the AneleanIllountain range have been c1eseribecl in lhe regiuumln Presently leafrust (eauseel by Puecinia lIilieil1a) is the most importantrust c1isease 01 wheat The utilisalion 01 suseeptible 01 moelerately suseeptible eultivars in a high ploportion 01 the wheatarea allows lhe pathogen to oversummer across large areas resulting in early onset 01 the epiclemics Severe epielemiescause important econolllie losses ifchemical control is not usecl The pathogen population is extremely e1ynamie leaclingto transitory resistance in commercial cultivars Lr34 is eoml11only present in the regional germplasm but there islimiteel knowleelge about the presence 01 other genes conferring resistanee in cultivars Genes Lr28 Lr36 Lr38 Lr4anel Lr43 proviele effective resislance in the region The best stralegy for the stabilisation ofthe pathogen population anelIesistanee is eonsielereel to be lhe use 01 aelult plant lCsistanee eonferreel by minol aelelitive genes inclueling Lr34 anelLr46 Sourees 01 this type uumlf resistanee from CIlvIfVlYT anel lhe region have been maele available to breeeling programsin the Southern Cone Stripe rust (P slriijortllis f sp Irifiei) is endemic in Chile where ehemieal control is requiredto prevent severe losscs in stripe rust susceptible eultivars Although new virulent raees emerge frequently resistancegcnes Yr5 V18 110 Yr5 anel YrS) are eurrently eifective in Chile Some important stripe rust epielcmics haveoceurred in Argentina Brazil anel Uruguay Avoieling lhe use 01 highly susceptible eultivars appears to be an effeetivestrategy to prevent stripe rust epielel11ic e1evelopment in this arca There have been no serious stem rust (P gralJlillis fsp Iriiei) epielel11ies for over 2 e1eeaelcs the e1isease was controlleel by rcsistant cultivars The most important genesconfcrring Iesistanee in Soutbern Cone gerlllpasm at the present time are plObably SI24 anel 513 Other effectivc genesare 5122 S125 Sr26 5132 Sr33 Sr35 SdY and S140 Several slem rllst sllsceptible wheat cultivars have re-cntlybcen relcaseel The increaseel cullivation of susceptiblc cultivars may leael to higher slelll rust ineielence increasing theprobability 01 appearancc 01 new viru1cnt races Since the 1BLI RS translocation possessing SI 31 is present in a highproportion 01 the regional germplasm lhe possiblc inlroeluction 01 slelll rust with Sr3 virlllence from A frica is 01great eoncem

Additional keywolds TriliclIllI aestivlllll PlIcciia Ilitieilla PIeoacutenia Slliifollllis f sp trilici Puccinia gralllinis f spIliliei pathogen variability resistance

Introductioll

Approxilllatcly 9million ha 01 eOlllmon (Triliellll aesfillIl1l) aneldurulll (T dllllllll) wheat was planteel annually in the SouthernConc of All1eriea (AIgentina Brazil Chile Paraguay anelUrllgllay) ellIring 2000-2004 (Tablc I) The average yield was23 tha resulting in a total annual proeluction of 211llillion t01 grain (FAOSTAT 2006) Durull1 wheats are sown only inArgentina and Chile anel represenl a low pereentage 01 theproduclion Argentina where an average 618 ll1illion haycarere planteel during 2000-2004 is lhe biggesl wheat produccr

followecl by Brazil (205Illillion ha) Chile (OAllllillion ha)Paraguay (O25Illillion ha) anel Urllguay (O14ll1illion ha)

Rusls are important e1iseases affecting cOllllllon wheatprociuction in the SOllthern Cone of South Amcrica eausingsevere losses if ehemical control is nol useel The cultivarsgrown (27 from Argentina 18 from Brazil 13 from Chile 9from Paraguay anel 10 from Uruguay) are largely moeleratelysusceptible 01 suseeptible to leal rllst eauseel by PlIcciniaIlilicina (Table I) Tn Argentina there is mocierate exposure toslern rust The estimatecl areas planted to cultivars with tbe

Table l Total approximate areas (ha x (000) SOWIl in 2004 to important cultivars to cultivars moderatelysusceptible or susceptible to leal lIld stem rusts and to cultivars known 10 carry lhe lBLlRS lranslocation

Estimated area sown to important cultivars somce Argentina area sown (ha) in 2004 Secretaria de Agricultura Pescay Alimelltacioacuten Brazil availabilily 01 cerlified seeel Departamento de Produccedilatildeo Vegetal SAA-RS Departamento deFiscalizaccedilatildeo e Defensa AgropecuaacuteriaDivisatildeo de Produccedilatildeo de Sementes SAA-PR Chile inscribed areas for 2002-2003Servicio Agriacutecola y Ganadero Paraguay Certified seed produced in 2004 Direccioacuten de Semillas MAG Uruguay areasown (ha) Encuesla Agriacutecola No 227 MGAP DJEA Presence 01 IBI R Source Rosa Filho 1997 G Tranquilli andL PJluumlger 2004 llnpllblished data R J Peiia 2003 llnpllblished data and indirect evidence by lhe presence 01 Lr26

(Antonelli 2003 Gcrmaacuten el 01 2005 Zoldan and Barcellos 2002)

COllntry Total Leafrust Stem rust lBLIRSArea () Area () Area ()

Argentina 54987 49791 906 17436 317 33923 617Brazil 17535 12317 702 952 54 5368 306Chile 1701 992 583 97 57 705 414Paraguay 3308 2431 735 00 00 1465 443Urugllay 1584 1129 7l2 227 143 336 212

Total 79116 66660 843 187l2 237 41797 528

1BLl RS translocation carrying stem rust resistance gene Sr31exceeeleel half of lhe total wheat area

lnforlllation on fielel reactions to leaf rusl (Tablc 1) wasavailable for ali cultivars The areas sown 10cultivars t110eleratelysusceptible or sllsccptible to stcm rust (P gral1linis f spIrilici) may be unelerestimateel since stcm rust reactions wereavailable only for 56 cllltivars anel some ofthe resistant cuitivarsmay not be precisely characteriseel elue to the absence of theelisease in t110st of the area eluring recent years The areassown to cultivars with the IBLIRS translocation are alsopossibly lInelerestimateel since the information onits presencewas available for 47 cultivars Information on stripe rust(P striiforlnis f sp Iriliei) fielel reactions was available only fromChile where susceptible anel moelerately susceptible cultivarsrepresentcel 647 of area sown to popular cultivars

In the Southern Cone wheat is planteel eluring the fali anelwinter Spring wheat is grown in Brazil anel Paraguay anel springanel facultative types grown in Argentina Chile anel UrllguayWinter types are grown in Southern Chile anel recently somewinter wheats have been releaseel in Argentina

In the Atlantic area (Argentin Brazil Paraguay anelUruguay) wheat is sown between latituele 18deg in Brazil anel38degS in Argcntina thus exteneling 2400 km from north to southThe crop is sown in iowlanels laquo400 m as I) in ArgentinaUruguay anel Paraguay anel on higher plateaux (600-800 masl) in Brazil Annual average rainfall varies frolll lt400 mm inthe south-western wheat region of Argentina to ncar 2000 t11111in the northem wheat region of Brazii in Paraguay averagcrainfall is 1600 mm anel Uruguay has an intermediate annualrainfall of about 1000 mm In the Pacific arca (Chile) wheat isplanteel in the central valley anel in some lower Alldcan rangesalong 2000 km between latitueles 27 anel 43degS More recentlythc crop has concentrateel in the southcrn areas (Iatitueles35-43degS) The annual rainfall pattem is opposite to that ofthe Atlantic area increasing from north to soulh where itreaches 2000 mmycar In bolh the Atlanlic anel lhe Pacificareas the earliest crops are planteel in the lowcr northernlatitueles anel laler crops are planteel in higher sOllthern latituelesClimatic conelitions in sOllthem Chile are very favourable forthe elevelopment ofstripe rllSt Leafrust anel stem rust epielemics

may occur throughout the entire Southern Cone except in south-westem Argentina where low humielity anel e1ew fonnation arelil11iting factors

The il11portance ofbleael wheat rust eliseases in the SouthernCone of South America pathogen variability the basis ofresistance of the regional germplasm anel strategics useel tocontrol these eliseases as well as perspectives for the futureVill be eliscusseel

Baseel on elifferences in the rusts race populations2 epielel11iological zones were suggesteel for the region(Rajaral11 anel Campos 1974) Chile representing the westernzone is separateel frol11 the eastem zone (Argentina BrazilParaguay and Urugllay) by the Anelean mountain rangeAccoreling to van Beuningen anel Kohli (1986) most areas inthe Southern Cone have fluctuating local winels in aelelitionto the preelominant weather pattems anel these are capable ofelistributing the spores in ali elirections The Anelean 1110untainrange appears to delay the movement of races between thezones As a result there are some similarities between the westanel east epielemiological zones in the P triticina population(Barcellos anel Kohli 2003) the P striiforlllis population (Straib1937) anel the P graminis f sp Iriliei population (Vallega1955) indicating migration between zones The presence ofraces of ali 3 rust pathogens common to Chile anel Argentina incereal crops in the Anelean valleys of Argentinean Rio Negroanel Neuqueacuten provinces (Vallega anel Favret 1947) also inelicatesa connection between the westem anel eastern cpielemiologicalzones

Stuelies on physiological specialisation of P gral7linis f sptrifiei anel P Iriticina ielentification of sources of resistanceanel testing of breeeling germplasm have a long traclitionin Argentina anel Brazil The first stuelies in the SouthernCone Vere conelucteel by G Ruelorf anel K Rosentiel inArgentina (Ruelorf et aI 1933) During 1938- 1943 rust researchwas carried out by J Vallega at the Instituto Fitoteacutecnicoele Santa Catalina anel eluring 1944-1952 by J Vallega anelE Favrct at the Instituto ele Fitotecnia in Castelar (Vallega

and Favret (952) Studies were continued by E Antonelliand other researchers until the 1990s at the Instituto Nacionalde Tecnologia Agropecuaria (INTA) Castelar ExperimentalStation This research was discontinued in 1997 and restarted in2002 by P Campos at INTA Experimental Station in BordenaveIn Brazil during 1949-1961 rust research was conductedby A Silva at the Instituto de Pesquisas e ExperimentaccedilatildeoAgropecuaacuteria do Sul (IPEAS) in Pelotas Rio Grande do Sul(da Silva 1966) and later by E Coelho and A BarcellosThe rust program was transferred to the Empresa Brasileirade Pesquisa Agropecuaacuteria (EMBRAPA) Centro Nacional dePesquisa de Trigo (CNPT) Passo Fundo RS also integratingother researchers (M Madeiros J Sartori M Chaves andothers) Since 2002 leaf rust studies have also been conductedat OR Melhoramento ele Sementes by A Barcellos anel C TurraStudies on physiological specialisation have been sporadic inChile (VoJovsky 1945 1946) while no studies of this type havebeen conelucteel in Paraguay Only a few studies were carried outin Uruguay before 1991 (Boasso and Levine 1951 Betucci et ai1971) when a program to stuely cereal rusts with emphasis onP triticilla was initiated at the Instituto Nacional ele InvestigacioacutenAgropecuaria (lNIA) by S Germaacuten Since 1975 leaf rust andstem rust samples from Chile anel Paraguay have been stuelicd inArgentina Brazil or Uruguay thus generating information forthe entire region

The exchange of germplasm and collaborative researchamong the Southern Cone countries and with the internationalcereal rust research cOlnmunity began in early 1900s whenwheat breeding was initiated in the region Resistance to wheatIcaf rust was present in the cultivars selected from lanelracesin the 1910s These selections were extensively exchangeelamong breeeling programs of Argentina Brazil anel UruguayHowever most ofthe germplasm developeel during 1910-1950was susceptible to stem rust Afier the stem rust epidemiccaused by race 15B in the USA anel Canada during 1950 alicountries in the Southern Cone participateel in the stem rustcontrol programleel by the University ofMinnesota The purposeof this international collaborative program was to evaluate theInternational Spring and Winter Wheat Rust Nurseries (lSWRNlWWR1J) from which sources ofresistance to the 3 rusts coulel beselected anel useel in breeeling programs During the 1960s rustresistant lines were also selected from germplasm distributcelby the Rockefeller Foundation and later by the [nternationalMaize anel Wheat Improvement Center (CIMMYT) basedin Mexico

Cooperative research on wheat rusts among ArgentinaBolivia Brazil Chile Paraguay and Uruguay was started in1975 The collaborative activities inclueled testing of advanccdlines from ali countries for stripe rust in elisease hotspotse1istribution anel evaluation of new sources of resistance toali 3 rusts evaluating new sources of aelult plant resistance(APR) to leaf rust including local germplasm anel anl1Ual leafrust anel stem rust race surveys More recent collaborativeresearch integrates elevelopment of molecular markers for leafrust resistance from Buck Manantial phenotyping C[MMYTmapping populations for APR to leaf rust elevelopmentof mapping populations from regional sources of elurableresistance anel introeluction of APR to regional germplasmThe organisation anel e1istribution of an ongoing annual Rust

Trap Nursery throughout the region was initiateel by Brazilin 1975 Results from the Trap Nursery have been reporteelby A Barcellos E Coelho and co-workers at regionalrust meetings Results trom 1998-2001 were summarised byBarcellos anel Kohli (2003)

Wheat leaf rustOistribution and occurrenceLeafrust is currently the most prevalent and severe wheat diseasein the Southern Cone (Kohli et ai 2003) 1t is present everyyear causing wielespreael epielemics depending on climaticconditions anel area sown to susceptible cultivars 1t causes severeepidemics in Brazil (Barcellos 1986) Paraguay (ele Viedmaand Bozzano 1986) and Uruguay (Germaacuten anel Kolmer 1994)In Argentina leaf rust is the most widespreael rust on wheat(Vallega anel Favret 1952) however only approximately 40 ofthe total area under wheat in Argentina is affecteel by se vereleaf rust epidemics (Germaacuten et ai 2004) [n the remainingArgentinean wheat area cool temperatures and dry conditionslimit the elisease elevelopment although the disease can beobserved over most of the wheat area In Chile leaf rust isincreasing in importance with more severe infections on winterand facultative wheats than on spring wheats (R Madariaga2003 pers comm)

Oversummering of leaf rust occurs over most of the regionLeaf rust has been observed in summer nurseries grownin southern Buenos Aires province and on volunteer plantsthroughout the Argentinean wheat area (Antonelli 2000) anel onvolunteer plants and trap nurseries planted during the summer inUruguay 10 Brazil susceptible plants in pots have been placeelin fields and later incubatecl resulting in stem rust and leafrust infections during most of the year (Barcellos et ai 1982Barcellos 1986) Leaf rust infections in commercial fielels arefirst observed in the north and develop with the crop towarels thesouth of the region (Barcellos et aI 1982)

Economic importanceA very high proportion of the wheat area in the Southern Coneis planted with susceptible or moelerately susceptible cultivars(Table 1) allowing widespreael local oversummering anel earlyonset of epielemics in the grOoving season The replacement ofsusceptible cultivars is relatively slow and the easy availabilityof fungicides that efficiently controI the elisease has prolongedthe lifespan of cOl1lmercially popular cultivars Losses causedby leaf rust can be gt50 in severe epidemics if fungicidesare not applied Losses estimated at US$170 million werecauseel by epielemics on 10 important cultivars grown in theregion eluring the period 1996-2003 (Germaacuten et aI 2004)Consielering the large areas sown to cultivars that requirechemical control in an average epielemic the total anlUal cost offungicidc applications to controlleafrust in the region is aboutUS$50 million

The use offungicides to control wheat leafrust differs al110ngcountries Fungicieles have been recommended since 1977 inBrazil have been useel widely in Paraguay since 1976 andhave been more cOl11l11onIy useel in Uruguay since the 1990s lnnormal epidemic conelitions at least 2 applications of fungiciclesare required to control the elisease on highly susceptible cultivars

1n Argentina one fungicide application to controllcafrust is usedon about 35 ofthe wheat area [n Chile the use offungicides tocontrolleafrust is not as common but in the last 5 years the useof chemical control has increased with the increased importanceof the disease

The pathogen population and important epidemicscaused by new virulent racesThe P trilicina population in the Southern Cone is extremelydynamic (Barcellos 2000 Antonelli 2003 Barcellos and Turra2004 Germaacuten et ai 2004 Chaves el aI 2005) A largc numberof races are generally present every year The prcvalence ofpathogen races changes dramatically over time in accorelancewith the area sown to cultivars susceptible to differentpathotypes After short periods of time with few exceptionsresistance of wielely grown cultivars is overcome by theappearance of virulent races of the pathogen (Barcellos 1982Antonelli 2003)

Information on the most important P Iriticina races foundin recent surveys (race frequency and year of first detection)is presenteel in Table 2 About 1700 isolates collecled inlhe region were stuelied during 2002-2004 Baseel on lheJ2 North American differenlials (Long anel Kolmer J989) anel2 supplementary elifferentials (TcLriO anel TcLr20 listed afterthe Prt code when races are virulent on lhese lines) about100 elifferent virulence combinations were identifiecl includingseveral new races Most races were present at low frequenciesThe number ofraces with fi-equencies gt 10 within a given yearvaried fram I to 4 Generally races found in high frequencyduring 2000-2004 were present in ali Southern Cone countrieswhereas races found in low frequency may have been present

in only one country Thp most important P Iriticina pathotypespresent in the region during the last 8 years were described byChaves ef aI (2005) and those present in Argentina eluring theast 2 years by Campos et aI (2005)

The prevalent races in the Southern Cone region are viruentfor Lrl Lr2a Lr2c Lr3a Ldka Lr10 Lri1 Lr14a Lr14bLr16 Lr17a Lr18 Lr20 Lr23 Lr24 Lr26 and Lr30 (Chaveset aI 2005) During the last 5 years virulence frequencies havegenerally been high on Iines with Lri Lda Ldka Lr10 Lr11Lr 17a Lr26 and LdO intermediate on lines with Lr20 andLr24 and low on those with Lr2a Lr2c and Lr9 Based on fielddata from the trap nurseries Barcellos and Kohli (2003) reportedthat genes Lr19 Lr21 Lr29 Ld2 Lr36 Lr42 anel Lr43 Vereeffective against the pathogen population present eluring 1998-2001 Since then infection on Lr 19 has been observeel in theregion 1n Uruguay seedling resistance genes Lr28 Ld8 andLr41 anel APR genes Lr22a anel Lr35 confer field resistanceLr34 is also effective throughout the region although it expressesonly a moderate leveI ofresistance when present singly

Races MFR MCD-JO20 MCP-I0 anel MDR-IO20 andrelated races have been important recently Races MFK MFTand MFR (Brazilian elesignation B40) overcame the resistanceof the popular Brazilian cultivars EMBRAPA 16 (Lr13 Lr24)anel OR 1 (Lr23 Lr24) and the Uruguayan cultivar INIA Cabureacute(Lr24) These races first combining virulence on Lr24 andLr26were important during 1997-2002 in Brazil and in 2001 inUruguay

Race MCD and related races MHD MI-lJ MHK and MI-lTali virulent for Lr 10 and Lr20 (Brazilian designation B48) werepresent at high frequencies in Brazil until 2003 in Uruguayuntil 2002 in Chile in 2001 in Paraguay in 2003 and at

Table 2 Virulence formula and frequellcy of Pllccillia frificil1 most importanl races idelllified ill lhe Southern Cone in samples collecleddurillg 2002-2004

SOllfce A Barcellos M Chaves P Campos S Gerl11aacuten unpllblished inforl11alion

Prt codeA and Brazi Virulence fonnula firSl detecliol1 2002 2003 2004v 011LrlO20 code Bra Urll Arg Bra Urll Arg Bra Par Urll Arg Bt3 Chio Urll

CCT-IO 33kaIOII172630 1998 168 112 08 47 05 10KDG-IO20 2a2c31 01 12024 1997 118LPJ-IO B44 191011172426 1997 98 07 08MCD-IO 13101726 2001 43 41 02 18 24 150MCD-IO20 B48 131 0172026 1999 1999 56 11 265 04 545 47 05 08 60MCG-IO B34 13101126 1989 1989 06 10 04 91 47 10 20MCl-IO B34 1310ll1726 1989 2003 66 99 06 10 81MCP-IO 133ka 10172630 2000 217 61 61 182 124 144 280MCP-1020 133ka I017202630 2002 224 l0 15 30 14 20MDR-1020 133ka101I202430 2003 06 10 170MrT B40 133ka1117242630 1994 126 02 12MFT-1020 B55 133ka 10111720242630 2004 65~IFT-20 B51 133ka 111 720242630 2003 77 116 05 1301vIHD-IO20 B48 1306171026 1999 109 70 05 24MImiddot[J-IO20 B-18 13101116172026 1999 71 145 65MI-IK-IO20 B48 1310111617202630 1999 55 96 53MIlP-IO 133kaIO 16172630 2002 20 168 220MHTmiddotIO B53 133kaIOII16172630 2003 496 07 306MHT-IO20 ll48 133ka1 0111617202630 1999 2002 120 l0 23 132 65 1000SPI-IO 850 I 1a2c91 011171426 2002 49 81 37TDD-IO20 B43 12a2c3IO I72014 1995 1995 12 05 23 296 24 20TFT B49 IJa 2c33kall 7 242630 2001 60 39 16TFT-20 B54 l2a2c33kaII172042630 2003 22 228

Total 110of samples per year 161 183 98 131 456 1i 169 209 246 100Total no ofraces 19 24 28 21 35 5 31 27 lt5 19TOlal no of races freg gt 10 4 3 2 2 3 2 2 3 2

A Long and Kolmer (1989)

10w frequencies in Argentina These raccs caused importantepielemics on the wielely sown Brazilian cultivar BRS 49 anel theUruguayan cultivars Estanzuela Peloacuten 90 (Lr1 Lr17 Lr26 Lr34Germaacuten and Kolmer 1996) and INJA Mirlo MCD-1O20 wasimportant in North America during 2002 (Kolmer et ai 2004R Singh 2003 pers comm) perhaps inelicating the occurrcnceof intercontinental migration

Race MCP-IO with a characteristic intennediate infectiontype on TcLr16 anel MHP-IO are probably the same race Thisrace was found in high frequency in Argentina during 2002-2004 in Uruguay during 2003-2004 and in Paraguay eluring2003 The leaf rust epielemics causeel by MCPMHP-I O on theArgentinean cultivar Klein Don Enriquc (Lr26 anel aelelitionalresistance Antonelli 2003) planted on over 2 million ha werevery severe and widespread during 2002 anel 2003

Race MDR-IO20 first identified in 2003 overcame theresistance ofthe Uruguayan cultivars JNIA Torcaza (Lr1 OLr24Germaacuten et ai 2005) anel INIA Churrinche anel the widelygrawn Brazilian cultivar Ocircnix The freq I c ufthis race rapidlyincreased in Uruguay during 2004 allll in tlgcntina anel Brazilin 2005

Some important epielemics that occurreel on rcgional cultivarssince the 1990s due to the spread of nces wirh new virulencecombinations were elescribed by Ant(nelli (2003) and Germaacutenet ai (2004)

Virulence has frequently elevelo)cd for effective resistancegenes eleployed in coml11ercial cultivlrs in the Southern ConeVirulence on wheats with Lr]6 8 1irst detected in Argentinain 1980 (Antonelli 2003) anel in il m 1982 (Barcellos 1986)Many CIMMYT lines anel dtiaiivc~ releaseel in the rcgion(Kohli anel Skovmanel 1997) became ~usceptible due to raceswith Lr26 virulence Virulence for Lr2middot first deteeted in 1981both in Argentina (Antonelli 1982) anci Brazil (Barcellos andAita 1982) caused extrell1ely severe epil emics durillg 1982 onthe Argentinean cultivar Cargill Trigal 8( 1 and on the cultivarTifton grown in Brazil Virulence for 1 --9 first detected inArgentina in 1982 (Antonelli 1986) causcl1 a major epidemicduring 1985 on the Argentinean cultivar La 1OzINTA grown inArgentina and Uruguay (Germaacuten et ai 1986) Virulence forLr3 7was first elemonstratecl in Uruguay in 1999 in race MCD-l 020which affected several cultivars that elonot carry LI 37 Virulenceon Lr19 was first observecl in 2004 in Paraguay (de Vieclll1a et ai

2(05) and Argentina where itwas verifiecl by E Antonelli (2005pers comm) During 2005 the Argentinean cultivar Pr01NTAGaucho which probably has Lri9 was severely affected by leafrust

Breeding for resistance

During the first period of wheat breeding in the rcgion leaf rustresistance was mainly clerived from locally adapted germplasmwhich in many cases was also used by breeding programs inother countries The Brazilian cultivar Frontana (Lri3 Lr34LrT3 and aelditional aelult plant resistance Dyck et ai 1966Dyck anel Samborski 1982 Singh and Rajarall1 1992) anel theArgentincan cultivar Buck Manantial (Lda or an allele Lri6and Lr17a Lri3 anel possibly Lr34 Dyek 1989) are sources ofelurable resistance that have bcen useel internationally Sourcesof resistance were selecteel from germplasm elistribulcel by

USDA since the 1950s and by the Rockefeller Foundation (IaterCJMMYT) since the 1960s Many CIMMYT 1ines elerived leafrust resistance from South American germplasm (Rajaram et aI1988)

Seeelling resistance genes present in the regional germplasmelevelopeel before 1960 areLr1 Lr3a Lrlbg Ldka Lri1 Lri4bLri6 anel Lr17a (Dyck and Samborski 1968a 1968b 1970Haggag anel Dyck 1973 Dyck andKerber 1977 Antonelli 1983Roelfs 1988 Dyck 1989 Kolmer et ai 2007 E F Antonelli2005 unpublished data) Two previously undesignated seeellingresislance genes temporari1y designated Lr7D anel Lr44d(originally present in the Argentinean cultivar Barletta 7Danel the Uruguayan cultivar Americano 44d respectively) weredescribecl by Antonelli (1994) Kolmer et ai (2007) founel apreviously unidelltified gene in Americano 25e

Aclult plant resistanee genes Lr12 Lr13 and Lr34 are alsopresent in the traditional gcrmplasm (Dyck el ai 1966 Dyck andSamborski 1982 Roelfs 1988 Dyck 1989 Singh and Rajaram1992 Kolmer et ai 2007) Brazilian cultivar BH 1146 hasLr13 and Ld4 (Kolmcr and Liu 20(1) Uneler the extremelyfavourab1e eonditions for leaf rust clevelopment present in theregion Lr34 and other APR genes were probably selected fromthe heterogeneous landrace cultivars and then mintained innewer cultivars Singh and Rajaram (1992) claimed evielencefor APR genes adelitional to LI13 anel Lr34 in frontana Kolmeret ai (2007) found one APR gene different from Lri2 LI 13 orLr34 in Americano 25e and 2 possibly unique A10R genes inAmericano 26n

More recently releasecl eultivars in South America havebeen clerivecl fram germplasm obtainecl from CIMMYT andother breeding programs Seedling resistance genes LI 10Lr14a Lr19 Lr23 Lr26 Lr27 and Ld1 (Singh andRajaram 1991 Singh 1993) may have been introduced VithCIMMYT germplasm Lr26 is probably the most widelydistributed of these genes since it is present in many high-yielcling CIMMYT lines (eg Veery Bobwhite Alondra Kauzand others) and clerivatives that have been used directlyas cultivars or in local crosses In Chile Lr26 was alsointroeluced through direct use of European wheats carryingthe 1BLI RS translocation (eg Aurora Kavkaz BezostayaLovrin Mildress Clement 1 Ramirez pers comm) Lr9 ispresent in Precoz Paranaacute INTA and its derivative La PazINTA (Antonelli 1983) Lr24 is present in Cargill Trigal800 (Antonelli 2003) and other Agent derivatives useel inbreeding programs in Argentina anel Uruguay anel in AmigoTi fton and Century useel in Brazil (Barcellos 1991 cited byZolelan and Barcellos 2002 The et ai 1991 McIntosh et ai1995) Lr34 and othcr APR genes conferring durable resistanceare wielely clistributed in CIMMYT gcrmplasm (Singh anelRajaram 1992 Singh and Huerta-Espino 1995) mostly clerivedfrom lraditional Southern Cone germplasm and in currentregional cultivars

Resistance genes LI 10 Lr23 Lr24 anel Lr26 most commonin Brazilian germplasm testeel during 1996-97 (Zoldan andBarcellos 2(02) continucd to be present in the most importantcultivars used in 2004 Lri3 and Lr34 are also widely presentin the Brazilian germplasm (Zoldan et ai 2000 de Sousa andBarcellos 2000 2001) together with other APR genes suchas Trpl anel Trp2 (temporary designatiol1) present il1 Toropiacute

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epielemics in most of the region (from Chile to Rio Graneleelo Sul in Brazil) causing extremely high losses in theeastern epielemio10gical zone (Boerger 1934 Vallega 1938)The presence in Argentina anel Uruguay of COl11l11onracesfounel in Chile (Straib 1937) inelicates stripe rust probablymigrateel through the Aneles liom Chile to the easteru part ofthe continent

Yr18 anel tightly linkeel Lr34 (McIntosh 1992 Singh1992) were probably present in tolerant wheat lines selecteeluneler the extreme 1929 anel 1930 stripe rust epielel11ics assuggesteel by Dyck (1991) anel Kolmer (1996) The Brazil iancultivar Fronteira one of Frontanas parents selecteel at BageacuteExperimental Station anel releaseel in 1934 was highly resistantto stripe rust (Beckmann 1940) ln Argentina cv Chino alsoknown as Chinese 166 expresseel the most effective resistanceanel was useel in crosses from which aelapteel resistant lines wereeleriveel (Val1ega 1938)

Unlike other regions of the worlel where the importanceof stripe rust is increasing no other wielespreael epielemichas occurreel in the eastern epielemiological zone anel theelisease is currently not economically important ln the southernwheat arca of Argentina only sporaelic localiseel outbreakshave been observeel on highly susceptible cultivars Similarloca1iseel epielemics have also been observeel in southern Brazilaifecting cv Curitiba eluring 1968 (Schraml11 1969) anel cvTifton eluring 1980 ln 1998 a moelerate epielemic ofstripe rustoccurreel in Uruguay (Germaacuten anel Caifare1 1999) During thisepielemic some cultivars with the lBLIRS translocation suchas Estanzuela Carelenal (Veery 3) were susceptible inelicatingthe presence ofvirulence on Yr9 Many cultivars known to carryYr18Lr34 hael 10w to intermeeliate stripe rust severities

Puccinia slriiformis probab1y oversummers in the valleys ofthe Argentinean Aneles (Neuqueacuten anel Rio Negro provinces)on wheat anel wilel Hordeum spp (Vallega anel Favret 1947)elelaying the elispersal ofinoculum to the major proeluction areasin the north Most germp1asl11 from Argentina Brazil Paraguayanel Urllguay is moelerately susceptible or susceptible uneler theheavy elisease conelitions present in Chile The absence ofearlyinfections even in the presence ofsusceptible cllltivars inelicatesthat inoculum is usually not present at early stages of cropelevelopment anel that oversummering does not regularly OCCllrin the l11ain wheat areas Uneler these conelitions avoieling theuse of highly susceptible cultivars anel maintaining resistancelevels such as those conferreel by Yr18 or other genes withsimilar eiacuteTect appears to be an effective strategy to prcvcntstripe rust epielemics in Uruguay (Germaacuten anel Caffarel 1999)anel the rest of the eastem epielemiologic zanc ln aelelitionthe increaseel use of durable APR to leaf rust often associatedwith APR to stripe rust (Singh 1992 Singh anel Rajaram 1994Singh el ai 2003) will also increase the leveI of resistance tostripe rust

Wheat stem rustOistribution and occurrenceAlthough the incielence of steni rust historically has been moresporaelic than that ofleafrust it causeel higher 1evels of elamageeluring severe epielemics It was consielereelthe most elestructivewheat rust in Brazil (ela Silva 1966) Paraguay (ele Vieelma anel

Bozzano 1986) Uruguay (Ribeiro 1952) the northem wheatgrowing area ofChile (Hacke 1990) anel the northern anel central-north wheat area of Argentina (Val1ega anel Favret 1952)

Oversummering of stem rust has been observeel on volunteerwheat anel barley plants in Uruguay anel in the south of BuenosAires province (Argentina) where it is frequently present in lhesummer nursery at Balcarce (1 Nisi 2005 pers comm) Stemrust also oversuml11ers locally in Brazil (Barcellos et ai 1982)

A very severe stem rust epielemic occurreel in Argentinaanel other Southern Cone countries in 1950 (Antonelli2000) The majority of commercia1 cultivars from regionalbreeeling programs were susceptible to the pathogen populationelominateel by a variant of race 15 (effective genesSr67a222425262731 ineffective genes Sr8a8bge9a9g1011 13173037 elenominateel 15 (63) by Antonel1i 1969)In 1974 a new race (effective genes Sr8a8bge11 2224252627313 7 ineffective genes Sr67a9a9gl 0131730elenominateel II MeR in Argentina anel Gil in Brazil)viru1ent on most of the popular Argentinean (Antonelli 2000)Brazilian (Coelho 1980) anel Uruguayan cultivars (Luizzi et aI1980) causeel wielespreael epielemics uneler unusually favourableenvironmenta1 conelitions eluring 1975-1976

Wheat stem rust has not been severely epielemic for over 2elecaeles This was coincielent with the increaseel anel wielespreaeluse ofcultivars with lBL1RS (Sr31) (Antonelli 2000) During1975-2003 2 stem rust epielemics (1976 anel 1981) wereobserveel inPasso funelo RS Brazil (C ele Souza 2005 perscomm) Localised epielemir outbreaks occurred during the1990s on some wielely grown cultivars in Paraguay (ltapuacutea35) Brazil (CEP 14) anel Argentina (Victoria lNTA) Since2000 stem rust has been observeel sporaelically on highlysusceptible materiaIs in experimental fields throughout lheregion The release of stem rust susceptible cultivars suchas Klein Escorpioacuten Buck Yatasto anel the French cultivarBaguette 10 led to the reappearance ofthe clisease in c0111mercialfielels in northern Argentina in 2001 anel 2003 (1 Nisi 2005 perscomm)

The pathogen populationDuring 1949-199430 elifferentP graminis races were elescribeelin Brazil These combineel virulence on 4 to 14 SI genes (Sr5Sr6 Sr7a Sr8 Sr9a Sr9b Srge SI10 SI11 Sr12 SI13 Sr14Sr17 Sr29 Sr30 SI36 Sr37) Most olel races ielentifieel inArgentina anel Brazil were lost from the collections elue toreeluction in research on stem rust Few races have been founelsince 2000 One race (RTT-TR Brazilian elesignation 030)has been prevalent for many years in Brazil anel UruguaySince 2002 some changes in the pathogen population havebeen eletecteel in Brazil (A Barcellos C ele Souza S GermaacutenC Turra anel M Segalin 2003 unpublisheel elata) Argentinaanel Uruguay Genes Sr22 Sr24 Sr25 Sr26 Sr31 Sr32 Sr33Sr35 Sr39 anel Sr40 are currently effective across the regionSr27hael intermeeliate stem rust severity levels in Chile in 1984(Hacke 1986) Sr38 has not been testeel although CIMMYT lineMilan that may carry this gene has hael high fielel severity withsusceptible reaction to stem rust in Uruguay anel Paraguay ln2005 a very severe stem rust epidemic on international nurseriesfTom CIMMYT anel the Southern Cone region was observeel inSanta Cruz Bolivia

Breeding for resistance

Stem rust resistance was one of the major wheat breeelingobjectives when the elisease was important acrass the regionln some countries stem rust resistance was a requirement forcultivar release Sources of stem rust resistance were selecteelfrom the same international nurseries useel to select for leaf rustresistance During the 1950s anel 1960s sources of resistanceielentifieel in Argentina were Kenya 58 Kenya 117A EgyptNA 10 1 some lines from Egypt N95 Kenya Governor KenyaStanelarel (VaI lega 1940) Mayo 54 Kentana 51A Yaqui 53 anelnew resistance ielentifieel fram the lSWRN (Antonelli 2000)ln Brazil the best sources of resistance provieleel to breeelingprograms were Reel Egyptian Kenya 58 anel Kenya FarmerCultivars with resistance fram these sources became wielespreael(ela Silva 1966)

Sr22 Sr24 Sr25 Sr26 S27 Sr31 Sr32 Sr33 (Coelho 19821986) anel Sr2 (C Sousa pers comm) have been useel inEMBRAPA-CNPT ln the Brazilian company OR sources withslow rusting type of resistance are being useel

Presently the most important genes conferring resistance inthe regional germplasm are Sr31 anel Sr24 The presence of S31is inelicateel by the presence ofthe 1BLl RS translocation anelorthe presence of Lr26 The presence of Lr24 inelicates the presenceof Sr24 The introeluction anel use ofSr31 anel Sr24 in the regionalgermplasm were as elescribeel for the 1inkeel leaf rust resistancegenes Although it is not known if S24 anel Sr31 are presentsingly 01 in combination with other resistance genes the basisof resistance in the regional germplasm appears to be narrowGenes Sr5 S6 S7a Sr8a Sr8b Sr9b Sr 10 S111 anel Sr30 areprobably present (but largely ineifective) in some Argentineancultivars (Antonelli 2000) APR genes such as S2 are presentin many Brazilian lines anel cultivars (C ele Souza 2005 persCOIllI11)

The absence ofthe elisease anel reeluceel pathogen variabilityhas elecreaseel the opportunities of selection for resistanceanel also the priority that breeeling programs have assigneel tothis characteristic As a result some susceptible cultivars havebeen recently releaseel inclueling some of European origino ltwas estimateel that gt20 of the regional vheat area in 2004was sown to cultivars known to be susceptib1e to stem rust(Table 1) anel this area continues to increase The increasingarea of susceptible cultivars 1ll)Y result not on1y in inoculumbuilel-up anel higher infections on these cultivars but also toan increaseel likelihooel of eleveloping new virulent races oncurrently resistant cultivars ln aelelition the introeluction ofraces with S24 virulence from South Africa 01 lnelia coulelcause significant losses Because the 1BL1 RS translocation ispresent in a high praportion of the regional germplasm (gt 50of the wheat area is sown with cultivars with this translocationTable 1) the possibility of introeluction of the Sr31 virulentrace Ug99 from Africa is of concern (Antouelli 2000 Germuacutenet aI 2005 1 Ramirez 2005 pers comm) This coulel resultin significant epielemics since elata obtaineel in Kenya eluring2005 inelicateel that the large majority of a group of 72 currentregional cultivars are sqsceptible 01 moelerately susceptible(R Wanyera 2005 pers comm) Given this situation stem rustmay increase in importance in the near future anel it is urgent toincrease testing for resistance to this elisease The introeluction

of resistance genes effective against races virulent on lineswith Sr31 anel Sr24 as well as other effective genes notpresent in the regional germplasm shoulel be emphasiseel(Germaacuten et alo 2005)

The control of wheat rusts continues to be a challengefor breeelers anel rust pathologists in the Southern Cone ofSouth America Breeeling wheat cultivars with effective anelmore elurable resistance is being aelelresseel using traelitionalmethoelologies as well as graelually introelucing newer tools tohelp increase know1eelge about rust resistance anel its efficientuse in breeeling

We appreciate the contribution of Dr Ricardo Madariaga INIA-Chile andDr Robert Mclntosh University of Sydney for reviewing the paper Muchoflhe information from 1999-2004 was obtained eluring the execution ofaproject funded by USDA Funeling ofthe attendance ofthe main author to thecon[erence Global Landscapes in Cereal Rust Control (September 2005)by GRDC is greatly appreciated

Aguayo L (1983) Mejoramiento ele trigos invernales y primaverales enIa zona centro-slU ele Chile In Relmiatildeo ele Melhoristas de Trigo doCone Sul EMBRAPA-CNPT Passo Fundo RS (Coord O de S Rosa)pp 91-100 Diaacutelogo No 9 (Programa Cooperativo dePesquisaAgricolaMontevieleo)

Anelrade Vilaro O (J 990) Polvillo estriado o roya amarilla (Puecilliastriiforlllis Westenel) deI trigo en Ia zona sur de Chile Institutoele Investigaciones Agropecuarias Estacioacuten Experimental CarillancaBoletiacuten Teacutecnico No 164 Temuco

Antonelli EF (1969) Fuentesde germoplasma ele resistencia a enfermeeladesy plagasln Simposio deI trigo Buenos Aires pp 332-351 (AcademiaNacional de AgronomIacutea y Veterinaria Buenos Aires)

Antonelli EF (1982) Especializacion fisioloacutegica ele Pueeillia reeonditatritiei y p gralllillis tritiei en Ia Argentina en el periacuteodo1978-1981 In Reunioacuten de Especialistas en Royas dei Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBID)

Antonelli EF (1983) Principales patoacutegenos que afectan Ia produccioacuten de trigoen Ia Argentina In Simposio sobre Fitomejoramiento y Produccioacuten eleCereales INTNCIMMYT Marcos Juaacuterez Coacutereloba [sp] (AgenciaEstadounidense para el Desarrollo Internacional Universielad Estatal deOregon)

Antonelli EF (1986) Especializacioacuten fisioloacutegica ele PlIeeillia recollditatritici y P gralllinis tritiei en Ia Argentina en el periacuteodo 1982-1984In Reuniatildeo ele Especialistas em Ferrugens de Cereais de InvernoCNPTErvtBRAPA Passo Funelo RS (Ed CJ Mofestina) pp 37-39Diaacutelogo No 13 (PROCISUR Montevideo)

Antonelli EF (1994) Resistencia en plaacutentula y planta adulta decultivares comerciales argentinos ele trigo y progenitores (antecesores)tradicionales In [nteraccioacuten hospedante-patoacutegeno en hongos biotrofosInforme correspondiente aI afio 1993 [sp] (Instituto ele Geneacutetica EAFavret Castelar)

Antonclli EF (2000) La roya negra dei tallo (PlIceilia gra111illisf sp tritiei)Una ilustre ausente de los campos de trigo (Por cuill1to tiempo mils bull(Grafos Necochea Argentina)

Antonelli EF (2003) La roya anaranjaela (PlIceinia triticillCl Erikss) SobreIa efiacutemera resistencia observada en Ia uacuteltima eleacutecada en cultivarescomerciales ele trigo ele amplia difusioacuten en Ia Argentina (GrafosNecochea Argentina)

Barcellos AL (1982) As ferrugens do trigo no Brasil In Trigo no Brasil(Coorel EA Osoacuterio) pp 377-419 (Flll1dacatildeo Cargill Campinas)

Barcellos AL (1986) Ferrugem da folha do trigo no Brasil Populaccedilatildeopatogecircnica fontes de resistecircncia trigos comerciais perpetuaccedilatildeo econtrole quiacutemico [n Reuniatildeo de Especialistas em Ferrugens de Cereaisde Inverno CNPTEMBRAPA Passo Flmdo RS (Ed CJ Molestina)pp 72-87 Diaacutelogo No 13 (PROC1SUR Montevideo)

Barcellos AL (1991) Dmable leaf rust resistance in wheat in BrazilIn Wheat for the non-traditional warm areas (Ed D Saunders)pp462-465 (C1lIMYT Meacutexico DF)

Barcellos AL (2000) Urgent need for less ephemeral resistance to leaf rustin Brazilian wheat cultivars In 6th International Wheat ConferenceAgricultural Research [nstitute of the 1-LmgarianAcadel11Yof SciencesMartonvaacutesaacuter Hungary

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Barcellos AL Aita L Coehlo ET (1982) Informaccedilotildees preliminares sobrefonte de inoacuteculo de ferrugem da folha e do colmo do trigo em PassoFundo [n Reunioacuten de Especialistas en Royas dcl Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBlD)

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Barcellos AL Roelfs AP de Moraes-Fernandes MIB (2000) Inheritance ofadult plant leaf rust resistance in the Brazilian wheat cultivar ToropiPan Disease 84 90-93

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BeckmaJm [(1940) EI problema dei trigo en el Brasil Revisla de a Faculadde AgronollIa (Monevideo) 19 21-36

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van Beuningen LT Kohli MM (1986) Resu1ts from the observalions onthe Latin Al11erican Rust Nursery (ELAR 1981-1983) In Reuniatildeo deEspecialistas em Ferrugens de Cereais de lI1Verno CNPTEMBRAPAPasso Funelo RS (Ed CJ Molestina) pp 7-20 Diaacutelogo No 13(PROC1SUR Montevieleo)

Boasso CS Levine MN (1951) Leaf rust of wheat Puccinia rubigoveraIriliei in Uruguay Phylopalhg) 41 736-741

Boerger A (1934) Consieleraeiones restropectivas acerca de Ia primeraaparieioacuten epieleacutemica ele Ia roya amarilla (Puceinia gullarull (Schm)Erikss et HeJU1)en el Riacuteo ele Ia Plata Revisla del Minislerio de [nduslrlas(Monlevideo) 15-16

Brammer SP Fernaneles MIB Barcellos AL Milach SCK (2004) Geneticanalysis of adult-plant resistanee to leaf rust in a elouble haploid wheat(Triliculll aeslivulll L em Thell) population Genelics and MoecuarBigy 27432-436 eloi I01590S 1415-47572004000300020

Bral11mer SP Worland A Bareellos AL Fernandez MIB (1998) lVlonosomieanalysis of adult-plant resistance to leaf rust in the BraziJian wheatcultivar Toropiacute 1n Proceeelings 9th International Wheat GeneticsSymposium Saskatoon Saskatchewan (Eel AE Slinkarel) v2pp 17-18 (University of Saskatchewan)

Campos PE Loacutepez JR Brach AM (2005) Characterization ofpopulation ofPuccinia Irilieina in Argentina in 2003 anel 2004 In Wheat proeluctionin stresseel envirornllents Abstracts of oral anel posteI presentationsof the 7th International Wheat Conference Mar elel Plata Argentinap I29 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Chaves MS Barcellos AL Germaacuten S Scheeren PL Dei Duca LeleJASilva M Soacute e Caieratildeo E (2005) Population elynamics of PlIccilialriticilain the South Cone region of South America In Wheat proeluction instresseel envirornllents Abstraets of oral anel poster presentations [ofthe] 7th International Wheat Conference Mar elel Plata Argentinap 130 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Coelho ET (1980) Distritribuccedilatildeo prevaJencia de novas razas fisiologicasde PlIccilia gmlllinis tritici (ferrugem do colmo elo trigo) no Brasil ele1974 a 1978 [n Xl Reuniatildeo Nacional de Pcsquisa ele Trigo PortoAlegre RS Brasil v 2 pp 9-22 (EMBRAPA Centro Nacional elePesquisa ele Trigo Passo Funelo)

Coelho E (1982) Siacutentese elos resultaelos elas pesquisas sobre ferrugem docolmo do trigo realizaelas no Centro Nacional ele Pesquisa ele Trigo(CNPT) EMBRAPA Passo FIUlelORS Brasil 1980 e 1981 In Reunioacutenele Especialistas en Royas elel Trigo Cono Sur ele Ameacuterica INTACastelar Argentina [sp] (Programa IlCA-Cono SurBlD)

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Dyck PL (1989) The inheritance of leaf rust resistance in wheat cultivarsKenyon anel B Manantial Caladial JOllma of Pall Seielce 691113-1117

Dyck PL (199 j) Genetics of aelult plant leaf rust resistance in ChineseSpring and Sturely wheats Crop Scielce 24 309-311

Dyck PL Kerber ER (1977) lnheritance of leaf rust resistance in wheatcultivars Rafaela anel EAP 26127 anel chromosome location of Irl7Caladial JOllma ofGelelics ald Cytgy 19 355-358

Dyck PL Samborski DL (1968a) Genetics of resistance to leaf rust in theconunon wheat varieties Webster Loros Brevit Carina Malakoff anelCentenario Caladial JOllma ofGelelics ald Cytgy 107-17

Dyck PL Samborski DL (1968b) Host-parasite interactions involvingtwo genes for leaf rust resistance in wheat ln Proceeelings of theThirel IJlternational Wheat Genetics Symposium Canberra Australia(Eels KW Finlay KW Shepherd) pp 245-250 (Australian Acaelemy ofScience Canberra)

Dyck PL Samborski DL (1970) The genetics of two alleles for leaf rustresistance at the [r14 locus in wheat Caladial JOllma of Gelelicsald C)lgy 12 689-694

Dyck PL Samborski DL (1982) The inheritance of resistance to Puceiliarecoldila in a group of conU110n wheat cultivars Caladial JOllma ofGelelics ald CylOogy 24273-283

Dyck PL Samborski DL Anelerson RG (1966) lnheritance of adultplant-Ieaf rust resistance eleriveel from the conmlon wleat varietiesExchange anel Frontana Caladial JOtlma oGelelics ald Cygy 8665-671

rlOSTAT (2006) Core production data (online) (FAO Rome) Availableat httpfaostatfaoorglsite340elefaultaspx Verifieel July 2006

Germaacuten S Caffarel JC (1999) Roya estriaela ele trigo In Jornaela de Cultivosele Invierno INIA La Estanzuela Colonia Uruguay pp 25-32 SerieActivielaeles ele Difusioacuten No 188 La Estanzuela

Germaacuten S Diaz M Verges R Castro M (2005) Breeeling for resistance towheat rusts in a highly favourable envirolUllent for eliseases In Wheatproeluction in stresseel envir Imlents Abstracts of oral anel posterpresentations [of theJ 7th International Wheat Conference Marelel Plata Argentina pp 139 (Secretariat of Agriculture AnimalHusbanelry fisheries anel Fooel)

and Favret (952) Studies were continued by E Antonelliand other researchers until the 1990s at the Instituto Nacionalde Tecnologia Agropecuaria (INTA) Castelar ExperimentalStation This research was discontinued in 1997 and restarted in2002 by P Campos at INTA Experimental Station in BordenaveIn Brazil during 1949-1961 rust research was conductedby A Silva at the Instituto de Pesquisas e ExperimentaccedilatildeoAgropecuaacuteria do Sul (IPEAS) in Pelotas Rio Grande do Sul(da Silva 1966) and later by E Coelho and A BarcellosThe rust program was transferred to the Empresa Brasileirade Pesquisa Agropecuaacuteria (EMBRAPA) Centro Nacional dePesquisa de Trigo (CNPT) Passo Fundo RS also integratingother researchers (M Madeiros J Sartori M Chaves andothers) Since 2002 leaf rust studies have also been conductedat OR Melhoramento ele Sementes by A Barcellos anel C TurraStudies on physiological specialisation have been sporadic inChile (VoJovsky 1945 1946) while no studies of this type havebeen conelucteel in Paraguay Only a few studies were carried outin Uruguay before 1991 (Boasso and Levine 1951 Betucci et ai1971) when a program to stuely cereal rusts with emphasis onP triticilla was initiated at the Instituto Nacional ele InvestigacioacutenAgropecuaria (lNIA) by S Germaacuten Since 1975 leaf rust andstem rust samples from Chile anel Paraguay have been stuelicd inArgentina Brazil or Uruguay thus generating information forthe entire region

The exchange of germplasm and collaborative researchamong the Southern Cone countries and with the internationalcereal rust research cOlnmunity began in early 1900s whenwheat breeding was initiated in the region Resistance to wheatIcaf rust was present in the cultivars selected from lanelracesin the 1910s These selections were extensively exchangeelamong breeeling programs of Argentina Brazil anel UruguayHowever most ofthe germplasm developeel during 1910-1950was susceptible to stem rust Afier the stem rust epidemiccaused by race 15B in the USA anel Canada during 1950 alicountries in the Southern Cone participateel in the stem rustcontrol programleel by the University ofMinnesota The purposeof this international collaborative program was to evaluate theInternational Spring and Winter Wheat Rust Nurseries (lSWRNlWWR1J) from which sources ofresistance to the 3 rusts coulel beselected anel useel in breeeling programs During the 1960s rustresistant lines were also selected from germplasm distributcelby the Rockefeller Foundation and later by the [nternationalMaize anel Wheat Improvement Center (CIMMYT) basedin Mexico

Cooperative research on wheat rusts among ArgentinaBolivia Brazil Chile Paraguay and Uruguay was started in1975 The collaborative activities inclueled testing of advanccdlines from ali countries for stripe rust in elisease hotspotse1istribution anel evaluation of new sources of resistance toali 3 rusts evaluating new sources of aelult plant resistance(APR) to leaf rust including local germplasm anel anl1Ual leafrust anel stem rust race surveys More recent collaborativeresearch integrates elevelopment of molecular markers for leafrust resistance from Buck Manantial phenotyping C[MMYTmapping populations for APR to leaf rust elevelopmentof mapping populations from regional sources of elurableresistance anel introeluction of APR to regional germplasmThe organisation anel e1istribution of an ongoing annual Rust

Trap Nursery throughout the region was initiateel by Brazilin 1975 Results from the Trap Nursery have been reporteelby A Barcellos E Coelho and co-workers at regionalrust meetings Results trom 1998-2001 were summarised byBarcellos anel Kohli (2003)

Wheat leaf rustOistribution and occurrenceLeafrust is currently the most prevalent and severe wheat diseasein the Southern Cone (Kohli et ai 2003) 1t is present everyyear causing wielespreael epielemics depending on climaticconditions anel area sown to susceptible cultivars 1t causes severeepidemics in Brazil (Barcellos 1986) Paraguay (ele Viedmaand Bozzano 1986) and Uruguay (Germaacuten anel Kolmer 1994)In Argentina leaf rust is the most widespreael rust on wheat(Vallega anel Favret 1952) however only approximately 40 ofthe total area under wheat in Argentina is affecteel by se vereleaf rust epidemics (Germaacuten et ai 2004) [n the remainingArgentinean wheat area cool temperatures and dry conditionslimit the elisease elevelopment although the disease can beobserved over most of the wheat area In Chile leaf rust isincreasing in importance with more severe infections on winterand facultative wheats than on spring wheats (R Madariaga2003 pers comm)

Oversummering of leaf rust occurs over most of the regionLeaf rust has been observed in summer nurseries grownin southern Buenos Aires province and on volunteer plantsthroughout the Argentinean wheat area (Antonelli 2000) anel onvolunteer plants and trap nurseries planted during the summer inUruguay 10 Brazil susceptible plants in pots have been placeelin fields and later incubatecl resulting in stem rust and leafrust infections during most of the year (Barcellos et ai 1982Barcellos 1986) Leaf rust infections in commercial fielels arefirst observed in the north and develop with the crop towarels thesouth of the region (Barcellos et aI 1982)

Economic importanceA very high proportion of the wheat area in the Southern Coneis planted with susceptible or moelerately susceptible cultivars(Table 1) allowing widespreael local oversummering anel earlyonset of epielemics in the grOoving season The replacement ofsusceptible cultivars is relatively slow and the easy availabilityof fungicides that efficiently controI the elisease has prolongedthe lifespan of cOl1lmercially popular cultivars Losses causedby leaf rust can be gt50 in severe epidemics if fungicidesare not applied Losses estimated at US$170 million werecauseel by epielemics on 10 important cultivars grown in theregion eluring the period 1996-2003 (Germaacuten et aI 2004)Consielering the large areas sown to cultivars that requirechemical control in an average epielemic the total anlUal cost offungicidc applications to controlleafrust in the region is aboutUS$50 million

The use offungicides to control wheat leafrust differs al110ngcountries Fungicieles have been recommended since 1977 inBrazil have been useel widely in Paraguay since 1976 andhave been more cOl11l11onIy useel in Uruguay since the 1990s lnnormal epidemic conelitions at least 2 applications of fungiciclesare required to control the elisease on highly susceptible cultivars

1n Argentina one fungicide application to controllcafrust is usedon about 35 ofthe wheat area [n Chile the use offungicides tocontrolleafrust is not as common but in the last 5 years the useof chemical control has increased with the increased importanceof the disease

The pathogen population and important epidemicscaused by new virulent racesThe P trilicina population in the Southern Cone is extremelydynamic (Barcellos 2000 Antonelli 2003 Barcellos and Turra2004 Germaacuten et ai 2004 Chaves el aI 2005) A largc numberof races are generally present every year The prcvalence ofpathogen races changes dramatically over time in accorelancewith the area sown to cultivars susceptible to differentpathotypes After short periods of time with few exceptionsresistance of wielely grown cultivars is overcome by theappearance of virulent races of the pathogen (Barcellos 1982Antonelli 2003)

Information on the most important P Iriticina races foundin recent surveys (race frequency and year of first detection)is presenteel in Table 2 About 1700 isolates collecled inlhe region were stuelied during 2002-2004 Baseel on lheJ2 North American differenlials (Long anel Kolmer J989) anel2 supplementary elifferentials (TcLriO anel TcLr20 listed afterthe Prt code when races are virulent on lhese lines) about100 elifferent virulence combinations were identifiecl includingseveral new races Most races were present at low frequenciesThe number ofraces with fi-equencies gt 10 within a given yearvaried fram I to 4 Generally races found in high frequencyduring 2000-2004 were present in ali Southern Cone countrieswhereas races found in low frequency may have been present

in only one country Thp most important P Iriticina pathotypespresent in the region during the last 8 years were described byChaves ef aI (2005) and those present in Argentina eluring theast 2 years by Campos et aI (2005)

The prevalent races in the Southern Cone region are viruentfor Lrl Lr2a Lr2c Lr3a Ldka Lr10 Lri1 Lr14a Lr14bLr16 Lr17a Lr18 Lr20 Lr23 Lr24 Lr26 and Lr30 (Chaveset aI 2005) During the last 5 years virulence frequencies havegenerally been high on Iines with Lri Lda Ldka Lr10 Lr11Lr 17a Lr26 and LdO intermediate on lines with Lr20 andLr24 and low on those with Lr2a Lr2c and Lr9 Based on fielddata from the trap nurseries Barcellos and Kohli (2003) reportedthat genes Lr19 Lr21 Lr29 Ld2 Lr36 Lr42 anel Lr43 Vereeffective against the pathogen population present eluring 1998-2001 Since then infection on Lr 19 has been observeel in theregion 1n Uruguay seedling resistance genes Lr28 Ld8 andLr41 anel APR genes Lr22a anel Lr35 confer field resistanceLr34 is also effective throughout the region although it expressesonly a moderate leveI ofresistance when present singly

Races MFR MCD-JO20 MCP-I0 anel MDR-IO20 andrelated races have been important recently Races MFK MFTand MFR (Brazilian elesignation B40) overcame the resistanceof the popular Brazilian cultivars EMBRAPA 16 (Lr13 Lr24)anel OR 1 (Lr23 Lr24) and the Uruguayan cultivar INIA Cabureacute(Lr24) These races first combining virulence on Lr24 andLr26were important during 1997-2002 in Brazil and in 2001 inUruguay

Race MCD and related races MHD MI-lJ MHK and MI-lTali virulent for Lr 10 and Lr20 (Brazilian designation B48) werepresent at high frequencies in Brazil until 2003 in Uruguayuntil 2002 in Chile in 2001 in Paraguay in 2003 and at

Table 2 Virulence formula and frequellcy of Pllccillia frificil1 most importanl races idelllified ill lhe Southern Cone in samples collecleddurillg 2002-2004

SOllfce A Barcellos M Chaves P Campos S Gerl11aacuten unpllblished inforl11alion

Prt codeA and Brazi Virulence fonnula firSl detecliol1 2002 2003 2004v 011LrlO20 code Bra Urll Arg Bra Urll Arg Bra Par Urll Arg Bt3 Chio Urll

CCT-IO 33kaIOII172630 1998 168 112 08 47 05 10KDG-IO20 2a2c31 01 12024 1997 118LPJ-IO B44 191011172426 1997 98 07 08MCD-IO 13101726 2001 43 41 02 18 24 150MCD-IO20 B48 131 0172026 1999 1999 56 11 265 04 545 47 05 08 60MCG-IO B34 13101126 1989 1989 06 10 04 91 47 10 20MCl-IO B34 1310ll1726 1989 2003 66 99 06 10 81MCP-IO 133ka 10172630 2000 217 61 61 182 124 144 280MCP-1020 133ka I017202630 2002 224 l0 15 30 14 20MDR-1020 133ka101I202430 2003 06 10 170MrT B40 133ka1117242630 1994 126 02 12MFT-1020 B55 133ka 10111720242630 2004 65~IFT-20 B51 133ka 111 720242630 2003 77 116 05 1301vIHD-IO20 B48 1306171026 1999 109 70 05 24MImiddot[J-IO20 B-18 13101116172026 1999 71 145 65MI-IK-IO20 B48 1310111617202630 1999 55 96 53MIlP-IO 133kaIO 16172630 2002 20 168 220MHTmiddotIO B53 133kaIOII16172630 2003 496 07 306MHT-IO20 ll48 133ka1 0111617202630 1999 2002 120 l0 23 132 65 1000SPI-IO 850 I 1a2c91 011171426 2002 49 81 37TDD-IO20 B43 12a2c3IO I72014 1995 1995 12 05 23 296 24 20TFT B49 IJa 2c33kall 7 242630 2001 60 39 16TFT-20 B54 l2a2c33kaII172042630 2003 22 228

Total 110of samples per year 161 183 98 131 456 1i 169 209 246 100Total no ofraces 19 24 28 21 35 5 31 27 lt5 19TOlal no of races freg gt 10 4 3 2 2 3 2 2 3 2

A Long and Kolmer (1989)

10w frequencies in Argentina These raccs caused importantepielemics on the wielely sown Brazilian cultivar BRS 49 anel theUruguayan cultivars Estanzuela Peloacuten 90 (Lr1 Lr17 Lr26 Lr34Germaacuten and Kolmer 1996) and INJA Mirlo MCD-1O20 wasimportant in North America during 2002 (Kolmer et ai 2004R Singh 2003 pers comm) perhaps inelicating the occurrcnceof intercontinental migration

Race MCP-IO with a characteristic intennediate infectiontype on TcLr16 anel MHP-IO are probably the same race Thisrace was found in high frequency in Argentina during 2002-2004 in Uruguay during 2003-2004 and in Paraguay eluring2003 The leaf rust epielemics causeel by MCPMHP-I O on theArgentinean cultivar Klein Don Enriquc (Lr26 anel aelelitionalresistance Antonelli 2003) planted on over 2 million ha werevery severe and widespread during 2002 anel 2003

Race MDR-IO20 first identified in 2003 overcame theresistance ofthe Uruguayan cultivars JNIA Torcaza (Lr1 OLr24Germaacuten et ai 2005) anel INIA Churrinche anel the widelygrawn Brazilian cultivar Ocircnix The freq I c ufthis race rapidlyincreased in Uruguay during 2004 allll in tlgcntina anel Brazilin 2005

Some important epielemics that occurreel on rcgional cultivarssince the 1990s due to the spread of nces wirh new virulencecombinations were elescribed by Ant(nelli (2003) and Germaacutenet ai (2004)

Virulence has frequently elevelo)cd for effective resistancegenes eleployed in coml11ercial cultivlrs in the Southern ConeVirulence on wheats with Lr]6 8 1irst detected in Argentinain 1980 (Antonelli 2003) anel in il m 1982 (Barcellos 1986)Many CIMMYT lines anel dtiaiivc~ releaseel in the rcgion(Kohli anel Skovmanel 1997) became ~usceptible due to raceswith Lr26 virulence Virulence for Lr2middot first deteeted in 1981both in Argentina (Antonelli 1982) anci Brazil (Barcellos andAita 1982) caused extrell1ely severe epil emics durillg 1982 onthe Argentinean cultivar Cargill Trigal 8( 1 and on the cultivarTifton grown in Brazil Virulence for 1 --9 first detected inArgentina in 1982 (Antonelli 1986) causcl1 a major epidemicduring 1985 on the Argentinean cultivar La 1OzINTA grown inArgentina and Uruguay (Germaacuten et ai 1986) Virulence forLr3 7was first elemonstratecl in Uruguay in 1999 in race MCD-l 020which affected several cultivars that elonot carry LI 37 Virulenceon Lr19 was first observecl in 2004 in Paraguay (de Vieclll1a et ai

2(05) and Argentina where itwas verifiecl by E Antonelli (2005pers comm) During 2005 the Argentinean cultivar Pr01NTAGaucho which probably has Lri9 was severely affected by leafrust

Breeding for resistance

During the first period of wheat breeding in the rcgion leaf rustresistance was mainly clerived from locally adapted germplasmwhich in many cases was also used by breeding programs inother countries The Brazilian cultivar Frontana (Lri3 Lr34LrT3 and aelditional aelult plant resistance Dyck et ai 1966Dyck anel Samborski 1982 Singh and Rajarall1 1992) anel theArgentincan cultivar Buck Manantial (Lda or an allele Lri6and Lr17a Lri3 anel possibly Lr34 Dyek 1989) are sources ofelurable resistance that have bcen useel internationally Sourcesof resistance were selecteel from germplasm elistribulcel by

USDA since the 1950s and by the Rockefeller Foundation (IaterCJMMYT) since the 1960s Many CIMMYT 1ines elerived leafrust resistance from South American germplasm (Rajaram et aI1988)

Seeelling resistance genes present in the regional germplasmelevelopeel before 1960 areLr1 Lr3a Lrlbg Ldka Lri1 Lri4bLri6 anel Lr17a (Dyck and Samborski 1968a 1968b 1970Haggag anel Dyck 1973 Dyck andKerber 1977 Antonelli 1983Roelfs 1988 Dyck 1989 Kolmer et ai 2007 E F Antonelli2005 unpublished data) Two previously undesignated seeellingresislance genes temporari1y designated Lr7D anel Lr44d(originally present in the Argentinean cultivar Barletta 7Danel the Uruguayan cultivar Americano 44d respectively) weredescribecl by Antonelli (1994) Kolmer et ai (2007) founel apreviously unidelltified gene in Americano 25e

Aclult plant resistanee genes Lr12 Lr13 and Lr34 are alsopresent in the traditional gcrmplasm (Dyck el ai 1966 Dyck andSamborski 1982 Roelfs 1988 Dyck 1989 Singh and Rajaram1992 Kolmer et ai 2007) Brazilian cultivar BH 1146 hasLr13 and Ld4 (Kolmcr and Liu 20(1) Uneler the extremelyfavourab1e eonditions for leaf rust clevelopment present in theregion Lr34 and other APR genes were probably selected fromthe heterogeneous landrace cultivars and then mintained innewer cultivars Singh and Rajaram (1992) claimed evielencefor APR genes adelitional to LI13 anel Lr34 in frontana Kolmeret ai (2007) found one APR gene different from Lri2 LI 13 orLr34 in Americano 25e and 2 possibly unique A10R genes inAmericano 26n

More recently releasecl eultivars in South America havebeen clerivecl fram germplasm obtainecl from CIMMYT andother breeding programs Seedling resistance genes LI 10Lr14a Lr19 Lr23 Lr26 Lr27 and Ld1 (Singh andRajaram 1991 Singh 1993) may have been introduced VithCIMMYT germplasm Lr26 is probably the most widelydistributed of these genes since it is present in many high-yielcling CIMMYT lines (eg Veery Bobwhite Alondra Kauzand others) and clerivatives that have been used directlyas cultivars or in local crosses In Chile Lr26 was alsointroeluced through direct use of European wheats carryingthe 1BLI RS translocation (eg Aurora Kavkaz BezostayaLovrin Mildress Clement 1 Ramirez pers comm) Lr9 ispresent in Precoz Paranaacute INTA and its derivative La PazINTA (Antonelli 1983) Lr24 is present in Cargill Trigal800 (Antonelli 2003) and other Agent derivatives useel inbreeding programs in Argentina anel Uruguay anel in AmigoTi fton and Century useel in Brazil (Barcellos 1991 cited byZolelan and Barcellos 2002 The et ai 1991 McIntosh et ai1995) Lr34 and othcr APR genes conferring durable resistanceare wielely clistributed in CIMMYT gcrmplasm (Singh anelRajaram 1992 Singh and Huerta-Espino 1995) mostly clerivedfrom lraditional Southern Cone germplasm and in currentregional cultivars

Resistance genes LI 10 Lr23 Lr24 anel Lr26 most commonin Brazilian germplasm testeel during 1996-97 (Zoldan andBarcellos 2(02) continucd to be present in the most importantcultivars used in 2004 Lri3 and Lr34 are also widely presentin the Brazilian germplasm (Zoldan et ai 2000 de Sousa andBarcellos 2000 2001) together with other APR genes suchas Trpl anel Trp2 (temporary designatiol1) present il1 Toropiacute

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epielemics in most of the region (from Chile to Rio Graneleelo Sul in Brazil) causing extremely high losses in theeastern epielemio10gical zone (Boerger 1934 Vallega 1938)The presence in Argentina anel Uruguay of COl11l11onracesfounel in Chile (Straib 1937) inelicates stripe rust probablymigrateel through the Aneles liom Chile to the easteru part ofthe continent

Yr18 anel tightly linkeel Lr34 (McIntosh 1992 Singh1992) were probably present in tolerant wheat lines selecteeluneler the extreme 1929 anel 1930 stripe rust epielel11ics assuggesteel by Dyck (1991) anel Kolmer (1996) The Brazil iancultivar Fronteira one of Frontanas parents selecteel at BageacuteExperimental Station anel releaseel in 1934 was highly resistantto stripe rust (Beckmann 1940) ln Argentina cv Chino alsoknown as Chinese 166 expresseel the most effective resistanceanel was useel in crosses from which aelapteel resistant lines wereeleriveel (Val1ega 1938)

Unlike other regions of the worlel where the importanceof stripe rust is increasing no other wielespreael epielemichas occurreel in the eastern epielemiological zone anel theelisease is currently not economically important ln the southernwheat arca of Argentina only sporaelic localiseel outbreakshave been observeel on highly susceptible cultivars Similarloca1iseel epielemics have also been observeel in southern Brazilaifecting cv Curitiba eluring 1968 (Schraml11 1969) anel cvTifton eluring 1980 ln 1998 a moelerate epielemic ofstripe rustoccurreel in Uruguay (Germaacuten anel Caifare1 1999) During thisepielemic some cultivars with the lBLIRS translocation suchas Estanzuela Carelenal (Veery 3) were susceptible inelicatingthe presence ofvirulence on Yr9 Many cultivars known to carryYr18Lr34 hael 10w to intermeeliate stripe rust severities

Puccinia slriiformis probab1y oversummers in the valleys ofthe Argentinean Aneles (Neuqueacuten anel Rio Negro provinces)on wheat anel wilel Hordeum spp (Vallega anel Favret 1947)elelaying the elispersal ofinoculum to the major proeluction areasin the north Most germp1asl11 from Argentina Brazil Paraguayanel Urllguay is moelerately susceptible or susceptible uneler theheavy elisease conelitions present in Chile The absence ofearlyinfections even in the presence ofsusceptible cllltivars inelicatesthat inoculum is usually not present at early stages of cropelevelopment anel that oversummering does not regularly OCCllrin the l11ain wheat areas Uneler these conelitions avoieling theuse of highly susceptible cultivars anel maintaining resistancelevels such as those conferreel by Yr18 or other genes withsimilar eiacuteTect appears to be an effective strategy to prcvcntstripe rust epielemics in Uruguay (Germaacuten anel Caffarel 1999)anel the rest of the eastem epielemiologic zanc ln aelelitionthe increaseel use of durable APR to leaf rust often associatedwith APR to stripe rust (Singh 1992 Singh anel Rajaram 1994Singh el ai 2003) will also increase the leveI of resistance tostripe rust

Wheat stem rustOistribution and occurrenceAlthough the incielence of steni rust historically has been moresporaelic than that ofleafrust it causeel higher 1evels of elamageeluring severe epielemics It was consielereelthe most elestructivewheat rust in Brazil (ela Silva 1966) Paraguay (ele Vieelma anel

Bozzano 1986) Uruguay (Ribeiro 1952) the northem wheatgrowing area ofChile (Hacke 1990) anel the northern anel central-north wheat area of Argentina (Val1ega anel Favret 1952)

Oversummering of stem rust has been observeel on volunteerwheat anel barley plants in Uruguay anel in the south of BuenosAires province (Argentina) where it is frequently present in lhesummer nursery at Balcarce (1 Nisi 2005 pers comm) Stemrust also oversuml11ers locally in Brazil (Barcellos et ai 1982)

A very severe stem rust epielemic occurreel in Argentinaanel other Southern Cone countries in 1950 (Antonelli2000) The majority of commercia1 cultivars from regionalbreeeling programs were susceptible to the pathogen populationelominateel by a variant of race 15 (effective genesSr67a222425262731 ineffective genes Sr8a8bge9a9g1011 13173037 elenominateel 15 (63) by Antonel1i 1969)In 1974 a new race (effective genes Sr8a8bge11 2224252627313 7 ineffective genes Sr67a9a9gl 0131730elenominateel II MeR in Argentina anel Gil in Brazil)viru1ent on most of the popular Argentinean (Antonelli 2000)Brazilian (Coelho 1980) anel Uruguayan cultivars (Luizzi et aI1980) causeel wielespreael epielemics uneler unusually favourableenvironmenta1 conelitions eluring 1975-1976

Wheat stem rust has not been severely epielemic for over 2elecaeles This was coincielent with the increaseel anel wielespreaeluse ofcultivars with lBL1RS (Sr31) (Antonelli 2000) During1975-2003 2 stem rust epielemics (1976 anel 1981) wereobserveel inPasso funelo RS Brazil (C ele Souza 2005 perscomm) Localised epielemir outbreaks occurred during the1990s on some wielely grown cultivars in Paraguay (ltapuacutea35) Brazil (CEP 14) anel Argentina (Victoria lNTA) Since2000 stem rust has been observeel sporaelically on highlysusceptible materiaIs in experimental fields throughout lheregion The release of stem rust susceptible cultivars suchas Klein Escorpioacuten Buck Yatasto anel the French cultivarBaguette 10 led to the reappearance ofthe clisease in c0111mercialfielels in northern Argentina in 2001 anel 2003 (1 Nisi 2005 perscomm)

The pathogen populationDuring 1949-199430 elifferentP graminis races were elescribeelin Brazil These combineel virulence on 4 to 14 SI genes (Sr5Sr6 Sr7a Sr8 Sr9a Sr9b Srge SI10 SI11 Sr12 SI13 Sr14Sr17 Sr29 Sr30 SI36 Sr37) Most olel races ielentifieel inArgentina anel Brazil were lost from the collections elue toreeluction in research on stem rust Few races have been founelsince 2000 One race (RTT-TR Brazilian elesignation 030)has been prevalent for many years in Brazil anel UruguaySince 2002 some changes in the pathogen population havebeen eletecteel in Brazil (A Barcellos C ele Souza S GermaacutenC Turra anel M Segalin 2003 unpublisheel elata) Argentinaanel Uruguay Genes Sr22 Sr24 Sr25 Sr26 Sr31 Sr32 Sr33Sr35 Sr39 anel Sr40 are currently effective across the regionSr27hael intermeeliate stem rust severity levels in Chile in 1984(Hacke 1986) Sr38 has not been testeel although CIMMYT lineMilan that may carry this gene has hael high fielel severity withsusceptible reaction to stem rust in Uruguay anel Paraguay ln2005 a very severe stem rust epidemic on international nurseriesfTom CIMMYT anel the Southern Cone region was observeel inSanta Cruz Bolivia

Breeding for resistance

Stem rust resistance was one of the major wheat breeelingobjectives when the elisease was important acrass the regionln some countries stem rust resistance was a requirement forcultivar release Sources of stem rust resistance were selecteelfrom the same international nurseries useel to select for leaf rustresistance During the 1950s anel 1960s sources of resistanceielentifieel in Argentina were Kenya 58 Kenya 117A EgyptNA 10 1 some lines from Egypt N95 Kenya Governor KenyaStanelarel (VaI lega 1940) Mayo 54 Kentana 51A Yaqui 53 anelnew resistance ielentifieel fram the lSWRN (Antonelli 2000)ln Brazil the best sources of resistance provieleel to breeelingprograms were Reel Egyptian Kenya 58 anel Kenya FarmerCultivars with resistance fram these sources became wielespreael(ela Silva 1966)

Sr22 Sr24 Sr25 Sr26 S27 Sr31 Sr32 Sr33 (Coelho 19821986) anel Sr2 (C Sousa pers comm) have been useel inEMBRAPA-CNPT ln the Brazilian company OR sources withslow rusting type of resistance are being useel

Presently the most important genes conferring resistance inthe regional germplasm are Sr31 anel Sr24 The presence of S31is inelicateel by the presence ofthe 1BLl RS translocation anelorthe presence of Lr26 The presence of Lr24 inelicates the presenceof Sr24 The introeluction anel use ofSr31 anel Sr24 in the regionalgermplasm were as elescribeel for the 1inkeel leaf rust resistancegenes Although it is not known if S24 anel Sr31 are presentsingly 01 in combination with other resistance genes the basisof resistance in the regional germplasm appears to be narrowGenes Sr5 S6 S7a Sr8a Sr8b Sr9b Sr 10 S111 anel Sr30 areprobably present (but largely ineifective) in some Argentineancultivars (Antonelli 2000) APR genes such as S2 are presentin many Brazilian lines anel cultivars (C ele Souza 2005 persCOIllI11)

The absence ofthe elisease anel reeluceel pathogen variabilityhas elecreaseel the opportunities of selection for resistanceanel also the priority that breeeling programs have assigneel tothis characteristic As a result some susceptible cultivars havebeen recently releaseel inclueling some of European origino ltwas estimateel that gt20 of the regional vheat area in 2004was sown to cultivars known to be susceptib1e to stem rust(Table 1) anel this area continues to increase The increasingarea of susceptible cultivars 1ll)Y result not on1y in inoculumbuilel-up anel higher infections on these cultivars but also toan increaseel likelihooel of eleveloping new virulent races oncurrently resistant cultivars ln aelelition the introeluction ofraces with S24 virulence from South Africa 01 lnelia coulelcause significant losses Because the 1BL1 RS translocation ispresent in a high praportion of the regional germplasm (gt 50of the wheat area is sown with cultivars with this translocationTable 1) the possibility of introeluction of the Sr31 virulentrace Ug99 from Africa is of concern (Antouelli 2000 Germuacutenet aI 2005 1 Ramirez 2005 pers comm) This coulel resultin significant epielemics since elata obtaineel in Kenya eluring2005 inelicateel that the large majority of a group of 72 currentregional cultivars are sqsceptible 01 moelerately susceptible(R Wanyera 2005 pers comm) Given this situation stem rustmay increase in importance in the near future anel it is urgent toincrease testing for resistance to this elisease The introeluction

of resistance genes effective against races virulent on lineswith Sr31 anel Sr24 as well as other effective genes notpresent in the regional germplasm shoulel be emphasiseel(Germaacuten et alo 2005)

The control of wheat rusts continues to be a challengefor breeelers anel rust pathologists in the Southern Cone ofSouth America Breeeling wheat cultivars with effective anelmore elurable resistance is being aelelresseel using traelitionalmethoelologies as well as graelually introelucing newer tools tohelp increase know1eelge about rust resistance anel its efficientuse in breeeling

We appreciate the contribution of Dr Ricardo Madariaga INIA-Chile andDr Robert Mclntosh University of Sydney for reviewing the paper Muchoflhe information from 1999-2004 was obtained eluring the execution ofaproject funded by USDA Funeling ofthe attendance ofthe main author to thecon[erence Global Landscapes in Cereal Rust Control (September 2005)by GRDC is greatly appreciated

Aguayo L (1983) Mejoramiento ele trigos invernales y primaverales enIa zona centro-slU ele Chile In Relmiatildeo ele Melhoristas de Trigo doCone Sul EMBRAPA-CNPT Passo Fundo RS (Coord O de S Rosa)pp 91-100 Diaacutelogo No 9 (Programa Cooperativo dePesquisaAgricolaMontevieleo)

Anelrade Vilaro O (J 990) Polvillo estriado o roya amarilla (Puecilliastriiforlllis Westenel) deI trigo en Ia zona sur de Chile Institutoele Investigaciones Agropecuarias Estacioacuten Experimental CarillancaBoletiacuten Teacutecnico No 164 Temuco

Antonelli EF (1969) Fuentesde germoplasma ele resistencia a enfermeeladesy plagasln Simposio deI trigo Buenos Aires pp 332-351 (AcademiaNacional de AgronomIacutea y Veterinaria Buenos Aires)

Antonelli EF (1982) Especializacion fisioloacutegica ele Pueeillia reeonditatritiei y p gralllillis tritiei en Ia Argentina en el periacuteodo1978-1981 In Reunioacuten de Especialistas en Royas dei Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBID)

Antonelli EF (1983) Principales patoacutegenos que afectan Ia produccioacuten de trigoen Ia Argentina In Simposio sobre Fitomejoramiento y Produccioacuten eleCereales INTNCIMMYT Marcos Juaacuterez Coacutereloba [sp] (AgenciaEstadounidense para el Desarrollo Internacional Universielad Estatal deOregon)

Antonelli EF (1986) Especializacioacuten fisioloacutegica ele PlIeeillia recollditatritici y P gralllinis tritiei en Ia Argentina en el periacuteodo 1982-1984In Reuniatildeo ele Especialistas em Ferrugens de Cereais de InvernoCNPTErvtBRAPA Passo Funelo RS (Ed CJ Mofestina) pp 37-39Diaacutelogo No 13 (PROCISUR Montevideo)

Antonelli EF (1994) Resistencia en plaacutentula y planta adulta decultivares comerciales argentinos ele trigo y progenitores (antecesores)tradicionales In [nteraccioacuten hospedante-patoacutegeno en hongos biotrofosInforme correspondiente aI afio 1993 [sp] (Instituto ele Geneacutetica EAFavret Castelar)

Antonclli EF (2000) La roya negra dei tallo (PlIceilia gra111illisf sp tritiei)Una ilustre ausente de los campos de trigo (Por cuill1to tiempo mils bull(Grafos Necochea Argentina)

Antonelli EF (2003) La roya anaranjaela (PlIceinia triticillCl Erikss) SobreIa efiacutemera resistencia observada en Ia uacuteltima eleacutecada en cultivarescomerciales ele trigo ele amplia difusioacuten en Ia Argentina (GrafosNecochea Argentina)

Barcellos AL (1982) As ferrugens do trigo no Brasil In Trigo no Brasil(Coorel EA Osoacuterio) pp 377-419 (Flll1dacatildeo Cargill Campinas)

Barcellos AL (1986) Ferrugem da folha do trigo no Brasil Populaccedilatildeopatogecircnica fontes de resistecircncia trigos comerciais perpetuaccedilatildeo econtrole quiacutemico [n Reuniatildeo de Especialistas em Ferrugens de Cereaisde Inverno CNPTEMBRAPA Passo Flmdo RS (Ed CJ Molestina)pp 72-87 Diaacutelogo No 13 (PROC1SUR Montevideo)

Barcellos AL (1991) Dmable leaf rust resistance in wheat in BrazilIn Wheat for the non-traditional warm areas (Ed D Saunders)pp462-465 (C1lIMYT Meacutexico DF)

Barcellos AL (2000) Urgent need for less ephemeral resistance to leaf rustin Brazilian wheat cultivars In 6th International Wheat ConferenceAgricultural Research [nstitute of the 1-LmgarianAcadel11Yof SciencesMartonvaacutesaacuter Hungary

Barcellos AL Aita L (1982) Siacutentese dos resultados das pesquisas sobreferrugem da folha do trigo realizadas no CNPT-EM BRPA Passo FundoRS Brasil de 1980 a 1982 In Reunioacuten de Especialistas en Royasdei Trigo Cono Sur de Ameacuterica INTA Castelar Argentina [sp](Programa IICA-Cono SmBlD)

Barcellos AL Aita L Coehlo ET (1982) Informaccedilotildees preliminares sobrefonte de inoacuteculo de ferrugem da folha e do colmo do trigo em PassoFundo [n Reunioacuten de Especialistas en Royas dcl Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBlD)

Barcellos AL Kohli MM (2003) Resultados da XI XII XlII e XIVcoleccedilatildeo para avaliaccedilatildeo e coleta de ferrugem do colmo e ferrugem dafolha do trigo 1998-2001 EMBRAPA TrigoC[MMYT Documentosno 37 Passo Fundo

Barcellos AL Roelfs AP de Moraes-Fernandes MIB (2000) Inheritance ofadult plant leaf rust resistance in the Brazilian wheat cultivar ToropiPan Disease 84 90-93

l3arcellos AL Tmra C (2004) Search for durable resistance to wheat leafrust in Brazil 1n Abstracts [ofthe] li th International Cereal Rusts andPowdery Mildews Conference Jolm lImes Centre Norwich EnglandUK p A23

Barcellos AL Turra C (2005) Partial resistance - best approach forcontrol of wheat leaf rust in envirolUnents favorable for the diseaseIn Wheat production in stressed envirolUnents abstracts of oral andposter presentations [of the] 7th 1nternational Vheat ConferenceMar dei Pbta Argentina pp 125 (Secretariat of Agriculture AnimalHusbandry Fisheries and Food)

BeckmaJm [(1940) EI problema dei trigo en el Brasil Revisla de a Faculadde AgronollIa (Monevideo) 19 21-36

Betucci L Ferreira V Szpiniak B (1971) Razas fisioloacutegicas ele Pucciniagrallinis Iriliei y Puccinia recondila Iriliei presentes en el Uruguay en1968 Universidael ele Ia Repuacuteblica Boletiacuten N~ 117 Montevideo

van Beuningen LT Kohli MM (1986) Resu1ts from the observalions onthe Latin Al11erican Rust Nursery (ELAR 1981-1983) In Reuniatildeo deEspecialistas em Ferrugens de Cereais de lI1Verno CNPTEMBRAPAPasso Funelo RS (Ed CJ Molestina) pp 7-20 Diaacutelogo No 13(PROC1SUR Montevieleo)

Boasso CS Levine MN (1951) Leaf rust of wheat Puccinia rubigoveraIriliei in Uruguay Phylopalhg) 41 736-741

Boerger A (1934) Consieleraeiones restropectivas acerca de Ia primeraaparieioacuten epieleacutemica ele Ia roya amarilla (Puceinia gullarull (Schm)Erikss et HeJU1)en el Riacuteo ele Ia Plata Revisla del Minislerio de [nduslrlas(Monlevideo) 15-16

Brammer SP Fernaneles MIB Barcellos AL Milach SCK (2004) Geneticanalysis of adult-plant resistanee to leaf rust in a elouble haploid wheat(Triliculll aeslivulll L em Thell) population Genelics and MoecuarBigy 27432-436 eloi I01590S 1415-47572004000300020

Bral11mer SP Worland A Bareellos AL Fernandez MIB (1998) lVlonosomieanalysis of adult-plant resistance to leaf rust in the BraziJian wheatcultivar Toropiacute 1n Proceeelings 9th International Wheat GeneticsSymposium Saskatoon Saskatchewan (Eel AE Slinkarel) v2pp 17-18 (University of Saskatchewan)

Campos PE Loacutepez JR Brach AM (2005) Characterization ofpopulation ofPuccinia Irilieina in Argentina in 2003 anel 2004 In Wheat proeluctionin stresseel envirornllents Abstracts of oral anel posteI presentationsof the 7th International Wheat Conference Mar elel Plata Argentinap I29 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Chaves MS Barcellos AL Germaacuten S Scheeren PL Dei Duca LeleJASilva M Soacute e Caieratildeo E (2005) Population elynamics of PlIccilialriticilain the South Cone region of South America In Wheat proeluction instresseel envirornllents Abstraets of oral anel poster presentations [ofthe] 7th International Wheat Conference Mar elel Plata Argentinap 130 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Coelho ET (1980) Distritribuccedilatildeo prevaJencia de novas razas fisiologicasde PlIccilia gmlllinis tritici (ferrugem do colmo elo trigo) no Brasil ele1974 a 1978 [n Xl Reuniatildeo Nacional de Pcsquisa ele Trigo PortoAlegre RS Brasil v 2 pp 9-22 (EMBRAPA Centro Nacional elePesquisa ele Trigo Passo Funelo)

Coelho E (1982) Siacutentese elos resultaelos elas pesquisas sobre ferrugem docolmo do trigo realizaelas no Centro Nacional ele Pesquisa ele Trigo(CNPT) EMBRAPA Passo FIUlelORS Brasil 1980 e 1981 In Reunioacutenele Especialistas en Royas elel Trigo Cono Sur ele Ameacuterica INTACastelar Argentina [sp] (Programa IlCA-Cono SurBlD)

Coelho E (1986) Siacutentese elos estuelos com ferrugem elo colmo elo trigo-1982 a 1984 In Reuniatildeo de Especialistas em Ferrugens ele Cereaisele Inverno CNPTIEMBRAPA Passo Funelo RS (Eel CJ Molestina)pp 107-110 Diaacutelogo No 13 (PROCISUR Montevieleo)

Dyck PL (1989) The inheritance of leaf rust resistance in wheat cultivarsKenyon anel B Manantial Caladial JOllma of Pall Seielce 691113-1117

Dyck PL (199 j) Genetics of aelult plant leaf rust resistance in ChineseSpring and Sturely wheats Crop Scielce 24 309-311

Dyck PL Kerber ER (1977) lnheritance of leaf rust resistance in wheatcultivars Rafaela anel EAP 26127 anel chromosome location of Irl7Caladial JOllma ofGelelics ald Cytgy 19 355-358

Dyck PL Samborski DL (1968a) Genetics of resistance to leaf rust in theconunon wheat varieties Webster Loros Brevit Carina Malakoff anelCentenario Caladial JOllma ofGelelics ald Cytgy 107-17

Dyck PL Samborski DL (1968b) Host-parasite interactions involvingtwo genes for leaf rust resistance in wheat ln Proceeelings of theThirel IJlternational Wheat Genetics Symposium Canberra Australia(Eels KW Finlay KW Shepherd) pp 245-250 (Australian Acaelemy ofScience Canberra)

Dyck PL Samborski DL (1970) The genetics of two alleles for leaf rustresistance at the [r14 locus in wheat Caladial JOllma of Gelelicsald C)lgy 12 689-694

Dyck PL Samborski DL (1982) The inheritance of resistance to Puceiliarecoldila in a group of conU110n wheat cultivars Caladial JOllma ofGelelics ald CylOogy 24273-283

Dyck PL Samborski DL Anelerson RG (1966) lnheritance of adultplant-Ieaf rust resistance eleriveel from the conmlon wleat varietiesExchange anel Frontana Caladial JOtlma oGelelics ald Cygy 8665-671

rlOSTAT (2006) Core production data (online) (FAO Rome) Availableat httpfaostatfaoorglsite340elefaultaspx Verifieel July 2006

Germaacuten S Caffarel JC (1999) Roya estriaela ele trigo In Jornaela de Cultivosele Invierno INIA La Estanzuela Colonia Uruguay pp 25-32 SerieActivielaeles ele Difusioacuten No 188 La Estanzuela

Germaacuten S Diaz M Verges R Castro M (2005) Breeeling for resistance towheat rusts in a highly favourable envirolUllent for eliseases In Wheatproeluction in stresseel envir Imlents Abstracts of oral anel posterpresentations [of theJ 7th International Wheat Conference Marelel Plata Argentina pp 139 (Secretariat of Agriculture AnimalHusbanelry fisheries anel Fooel)

1n Argentina one fungicide application to controllcafrust is usedon about 35 ofthe wheat area [n Chile the use offungicides tocontrolleafrust is not as common but in the last 5 years the useof chemical control has increased with the increased importanceof the disease

The pathogen population and important epidemicscaused by new virulent racesThe P trilicina population in the Southern Cone is extremelydynamic (Barcellos 2000 Antonelli 2003 Barcellos and Turra2004 Germaacuten et ai 2004 Chaves el aI 2005) A largc numberof races are generally present every year The prcvalence ofpathogen races changes dramatically over time in accorelancewith the area sown to cultivars susceptible to differentpathotypes After short periods of time with few exceptionsresistance of wielely grown cultivars is overcome by theappearance of virulent races of the pathogen (Barcellos 1982Antonelli 2003)

Information on the most important P Iriticina races foundin recent surveys (race frequency and year of first detection)is presenteel in Table 2 About 1700 isolates collecled inlhe region were stuelied during 2002-2004 Baseel on lheJ2 North American differenlials (Long anel Kolmer J989) anel2 supplementary elifferentials (TcLriO anel TcLr20 listed afterthe Prt code when races are virulent on lhese lines) about100 elifferent virulence combinations were identifiecl includingseveral new races Most races were present at low frequenciesThe number ofraces with fi-equencies gt 10 within a given yearvaried fram I to 4 Generally races found in high frequencyduring 2000-2004 were present in ali Southern Cone countrieswhereas races found in low frequency may have been present

in only one country Thp most important P Iriticina pathotypespresent in the region during the last 8 years were described byChaves ef aI (2005) and those present in Argentina eluring theast 2 years by Campos et aI (2005)

The prevalent races in the Southern Cone region are viruentfor Lrl Lr2a Lr2c Lr3a Ldka Lr10 Lri1 Lr14a Lr14bLr16 Lr17a Lr18 Lr20 Lr23 Lr24 Lr26 and Lr30 (Chaveset aI 2005) During the last 5 years virulence frequencies havegenerally been high on Iines with Lri Lda Ldka Lr10 Lr11Lr 17a Lr26 and LdO intermediate on lines with Lr20 andLr24 and low on those with Lr2a Lr2c and Lr9 Based on fielddata from the trap nurseries Barcellos and Kohli (2003) reportedthat genes Lr19 Lr21 Lr29 Ld2 Lr36 Lr42 anel Lr43 Vereeffective against the pathogen population present eluring 1998-2001 Since then infection on Lr 19 has been observeel in theregion 1n Uruguay seedling resistance genes Lr28 Ld8 andLr41 anel APR genes Lr22a anel Lr35 confer field resistanceLr34 is also effective throughout the region although it expressesonly a moderate leveI ofresistance when present singly

Races MFR MCD-JO20 MCP-I0 anel MDR-IO20 andrelated races have been important recently Races MFK MFTand MFR (Brazilian elesignation B40) overcame the resistanceof the popular Brazilian cultivars EMBRAPA 16 (Lr13 Lr24)anel OR 1 (Lr23 Lr24) and the Uruguayan cultivar INIA Cabureacute(Lr24) These races first combining virulence on Lr24 andLr26were important during 1997-2002 in Brazil and in 2001 inUruguay

Race MCD and related races MHD MI-lJ MHK and MI-lTali virulent for Lr 10 and Lr20 (Brazilian designation B48) werepresent at high frequencies in Brazil until 2003 in Uruguayuntil 2002 in Chile in 2001 in Paraguay in 2003 and at

Table 2 Virulence formula and frequellcy of Pllccillia frificil1 most importanl races idelllified ill lhe Southern Cone in samples collecleddurillg 2002-2004

SOllfce A Barcellos M Chaves P Campos S Gerl11aacuten unpllblished inforl11alion

Prt codeA and Brazi Virulence fonnula firSl detecliol1 2002 2003 2004v 011LrlO20 code Bra Urll Arg Bra Urll Arg Bra Par Urll Arg Bt3 Chio Urll

CCT-IO 33kaIOII172630 1998 168 112 08 47 05 10KDG-IO20 2a2c31 01 12024 1997 118LPJ-IO B44 191011172426 1997 98 07 08MCD-IO 13101726 2001 43 41 02 18 24 150MCD-IO20 B48 131 0172026 1999 1999 56 11 265 04 545 47 05 08 60MCG-IO B34 13101126 1989 1989 06 10 04 91 47 10 20MCl-IO B34 1310ll1726 1989 2003 66 99 06 10 81MCP-IO 133ka 10172630 2000 217 61 61 182 124 144 280MCP-1020 133ka I017202630 2002 224 l0 15 30 14 20MDR-1020 133ka101I202430 2003 06 10 170MrT B40 133ka1117242630 1994 126 02 12MFT-1020 B55 133ka 10111720242630 2004 65~IFT-20 B51 133ka 111 720242630 2003 77 116 05 1301vIHD-IO20 B48 1306171026 1999 109 70 05 24MImiddot[J-IO20 B-18 13101116172026 1999 71 145 65MI-IK-IO20 B48 1310111617202630 1999 55 96 53MIlP-IO 133kaIO 16172630 2002 20 168 220MHTmiddotIO B53 133kaIOII16172630 2003 496 07 306MHT-IO20 ll48 133ka1 0111617202630 1999 2002 120 l0 23 132 65 1000SPI-IO 850 I 1a2c91 011171426 2002 49 81 37TDD-IO20 B43 12a2c3IO I72014 1995 1995 12 05 23 296 24 20TFT B49 IJa 2c33kall 7 242630 2001 60 39 16TFT-20 B54 l2a2c33kaII172042630 2003 22 228

Total 110of samples per year 161 183 98 131 456 1i 169 209 246 100Total no ofraces 19 24 28 21 35 5 31 27 lt5 19TOlal no of races freg gt 10 4 3 2 2 3 2 2 3 2

A Long and Kolmer (1989)

10w frequencies in Argentina These raccs caused importantepielemics on the wielely sown Brazilian cultivar BRS 49 anel theUruguayan cultivars Estanzuela Peloacuten 90 (Lr1 Lr17 Lr26 Lr34Germaacuten and Kolmer 1996) and INJA Mirlo MCD-1O20 wasimportant in North America during 2002 (Kolmer et ai 2004R Singh 2003 pers comm) perhaps inelicating the occurrcnceof intercontinental migration

Race MCP-IO with a characteristic intennediate infectiontype on TcLr16 anel MHP-IO are probably the same race Thisrace was found in high frequency in Argentina during 2002-2004 in Uruguay during 2003-2004 and in Paraguay eluring2003 The leaf rust epielemics causeel by MCPMHP-I O on theArgentinean cultivar Klein Don Enriquc (Lr26 anel aelelitionalresistance Antonelli 2003) planted on over 2 million ha werevery severe and widespread during 2002 anel 2003

Race MDR-IO20 first identified in 2003 overcame theresistance ofthe Uruguayan cultivars JNIA Torcaza (Lr1 OLr24Germaacuten et ai 2005) anel INIA Churrinche anel the widelygrawn Brazilian cultivar Ocircnix The freq I c ufthis race rapidlyincreased in Uruguay during 2004 allll in tlgcntina anel Brazilin 2005

Some important epielemics that occurreel on rcgional cultivarssince the 1990s due to the spread of nces wirh new virulencecombinations were elescribed by Ant(nelli (2003) and Germaacutenet ai (2004)

Virulence has frequently elevelo)cd for effective resistancegenes eleployed in coml11ercial cultivlrs in the Southern ConeVirulence on wheats with Lr]6 8 1irst detected in Argentinain 1980 (Antonelli 2003) anel in il m 1982 (Barcellos 1986)Many CIMMYT lines anel dtiaiivc~ releaseel in the rcgion(Kohli anel Skovmanel 1997) became ~usceptible due to raceswith Lr26 virulence Virulence for Lr2middot first deteeted in 1981both in Argentina (Antonelli 1982) anci Brazil (Barcellos andAita 1982) caused extrell1ely severe epil emics durillg 1982 onthe Argentinean cultivar Cargill Trigal 8( 1 and on the cultivarTifton grown in Brazil Virulence for 1 --9 first detected inArgentina in 1982 (Antonelli 1986) causcl1 a major epidemicduring 1985 on the Argentinean cultivar La 1OzINTA grown inArgentina and Uruguay (Germaacuten et ai 1986) Virulence forLr3 7was first elemonstratecl in Uruguay in 1999 in race MCD-l 020which affected several cultivars that elonot carry LI 37 Virulenceon Lr19 was first observecl in 2004 in Paraguay (de Vieclll1a et ai

2(05) and Argentina where itwas verifiecl by E Antonelli (2005pers comm) During 2005 the Argentinean cultivar Pr01NTAGaucho which probably has Lri9 was severely affected by leafrust

Breeding for resistance

During the first period of wheat breeding in the rcgion leaf rustresistance was mainly clerived from locally adapted germplasmwhich in many cases was also used by breeding programs inother countries The Brazilian cultivar Frontana (Lri3 Lr34LrT3 and aelditional aelult plant resistance Dyck et ai 1966Dyck anel Samborski 1982 Singh and Rajarall1 1992) anel theArgentincan cultivar Buck Manantial (Lda or an allele Lri6and Lr17a Lri3 anel possibly Lr34 Dyek 1989) are sources ofelurable resistance that have bcen useel internationally Sourcesof resistance were selecteel from germplasm elistribulcel by

USDA since the 1950s and by the Rockefeller Foundation (IaterCJMMYT) since the 1960s Many CIMMYT 1ines elerived leafrust resistance from South American germplasm (Rajaram et aI1988)

Seeelling resistance genes present in the regional germplasmelevelopeel before 1960 areLr1 Lr3a Lrlbg Ldka Lri1 Lri4bLri6 anel Lr17a (Dyck and Samborski 1968a 1968b 1970Haggag anel Dyck 1973 Dyck andKerber 1977 Antonelli 1983Roelfs 1988 Dyck 1989 Kolmer et ai 2007 E F Antonelli2005 unpublished data) Two previously undesignated seeellingresislance genes temporari1y designated Lr7D anel Lr44d(originally present in the Argentinean cultivar Barletta 7Danel the Uruguayan cultivar Americano 44d respectively) weredescribecl by Antonelli (1994) Kolmer et ai (2007) founel apreviously unidelltified gene in Americano 25e

Aclult plant resistanee genes Lr12 Lr13 and Lr34 are alsopresent in the traditional gcrmplasm (Dyck el ai 1966 Dyck andSamborski 1982 Roelfs 1988 Dyck 1989 Singh and Rajaram1992 Kolmer et ai 2007) Brazilian cultivar BH 1146 hasLr13 and Ld4 (Kolmcr and Liu 20(1) Uneler the extremelyfavourab1e eonditions for leaf rust clevelopment present in theregion Lr34 and other APR genes were probably selected fromthe heterogeneous landrace cultivars and then mintained innewer cultivars Singh and Rajaram (1992) claimed evielencefor APR genes adelitional to LI13 anel Lr34 in frontana Kolmeret ai (2007) found one APR gene different from Lri2 LI 13 orLr34 in Americano 25e and 2 possibly unique A10R genes inAmericano 26n

More recently releasecl eultivars in South America havebeen clerivecl fram germplasm obtainecl from CIMMYT andother breeding programs Seedling resistance genes LI 10Lr14a Lr19 Lr23 Lr26 Lr27 and Ld1 (Singh andRajaram 1991 Singh 1993) may have been introduced VithCIMMYT germplasm Lr26 is probably the most widelydistributed of these genes since it is present in many high-yielcling CIMMYT lines (eg Veery Bobwhite Alondra Kauzand others) and clerivatives that have been used directlyas cultivars or in local crosses In Chile Lr26 was alsointroeluced through direct use of European wheats carryingthe 1BLI RS translocation (eg Aurora Kavkaz BezostayaLovrin Mildress Clement 1 Ramirez pers comm) Lr9 ispresent in Precoz Paranaacute INTA and its derivative La PazINTA (Antonelli 1983) Lr24 is present in Cargill Trigal800 (Antonelli 2003) and other Agent derivatives useel inbreeding programs in Argentina anel Uruguay anel in AmigoTi fton and Century useel in Brazil (Barcellos 1991 cited byZolelan and Barcellos 2002 The et ai 1991 McIntosh et ai1995) Lr34 and othcr APR genes conferring durable resistanceare wielely clistributed in CIMMYT gcrmplasm (Singh anelRajaram 1992 Singh and Huerta-Espino 1995) mostly clerivedfrom lraditional Southern Cone germplasm and in currentregional cultivars

Resistance genes LI 10 Lr23 Lr24 anel Lr26 most commonin Brazilian germplasm testeel during 1996-97 (Zoldan andBarcellos 2(02) continucd to be present in the most importantcultivars used in 2004 Lri3 and Lr34 are also widely presentin the Brazilian germplasm (Zoldan et ai 2000 de Sousa andBarcellos 2000 2001) together with other APR genes suchas Trpl anel Trp2 (temporary designatiol1) present il1 Toropiacute

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epielemics in most of the region (from Chile to Rio Graneleelo Sul in Brazil) causing extremely high losses in theeastern epielemio10gical zone (Boerger 1934 Vallega 1938)The presence in Argentina anel Uruguay of COl11l11onracesfounel in Chile (Straib 1937) inelicates stripe rust probablymigrateel through the Aneles liom Chile to the easteru part ofthe continent

Yr18 anel tightly linkeel Lr34 (McIntosh 1992 Singh1992) were probably present in tolerant wheat lines selecteeluneler the extreme 1929 anel 1930 stripe rust epielel11ics assuggesteel by Dyck (1991) anel Kolmer (1996) The Brazil iancultivar Fronteira one of Frontanas parents selecteel at BageacuteExperimental Station anel releaseel in 1934 was highly resistantto stripe rust (Beckmann 1940) ln Argentina cv Chino alsoknown as Chinese 166 expresseel the most effective resistanceanel was useel in crosses from which aelapteel resistant lines wereeleriveel (Val1ega 1938)

Unlike other regions of the worlel where the importanceof stripe rust is increasing no other wielespreael epielemichas occurreel in the eastern epielemiological zone anel theelisease is currently not economically important ln the southernwheat arca of Argentina only sporaelic localiseel outbreakshave been observeel on highly susceptible cultivars Similarloca1iseel epielemics have also been observeel in southern Brazilaifecting cv Curitiba eluring 1968 (Schraml11 1969) anel cvTifton eluring 1980 ln 1998 a moelerate epielemic ofstripe rustoccurreel in Uruguay (Germaacuten anel Caifare1 1999) During thisepielemic some cultivars with the lBLIRS translocation suchas Estanzuela Carelenal (Veery 3) were susceptible inelicatingthe presence ofvirulence on Yr9 Many cultivars known to carryYr18Lr34 hael 10w to intermeeliate stripe rust severities

Puccinia slriiformis probab1y oversummers in the valleys ofthe Argentinean Aneles (Neuqueacuten anel Rio Negro provinces)on wheat anel wilel Hordeum spp (Vallega anel Favret 1947)elelaying the elispersal ofinoculum to the major proeluction areasin the north Most germp1asl11 from Argentina Brazil Paraguayanel Urllguay is moelerately susceptible or susceptible uneler theheavy elisease conelitions present in Chile The absence ofearlyinfections even in the presence ofsusceptible cllltivars inelicatesthat inoculum is usually not present at early stages of cropelevelopment anel that oversummering does not regularly OCCllrin the l11ain wheat areas Uneler these conelitions avoieling theuse of highly susceptible cultivars anel maintaining resistancelevels such as those conferreel by Yr18 or other genes withsimilar eiacuteTect appears to be an effective strategy to prcvcntstripe rust epielemics in Uruguay (Germaacuten anel Caffarel 1999)anel the rest of the eastem epielemiologic zanc ln aelelitionthe increaseel use of durable APR to leaf rust often associatedwith APR to stripe rust (Singh 1992 Singh anel Rajaram 1994Singh el ai 2003) will also increase the leveI of resistance tostripe rust

Wheat stem rustOistribution and occurrenceAlthough the incielence of steni rust historically has been moresporaelic than that ofleafrust it causeel higher 1evels of elamageeluring severe epielemics It was consielereelthe most elestructivewheat rust in Brazil (ela Silva 1966) Paraguay (ele Vieelma anel

Bozzano 1986) Uruguay (Ribeiro 1952) the northem wheatgrowing area ofChile (Hacke 1990) anel the northern anel central-north wheat area of Argentina (Val1ega anel Favret 1952)

Oversummering of stem rust has been observeel on volunteerwheat anel barley plants in Uruguay anel in the south of BuenosAires province (Argentina) where it is frequently present in lhesummer nursery at Balcarce (1 Nisi 2005 pers comm) Stemrust also oversuml11ers locally in Brazil (Barcellos et ai 1982)

A very severe stem rust epielemic occurreel in Argentinaanel other Southern Cone countries in 1950 (Antonelli2000) The majority of commercia1 cultivars from regionalbreeeling programs were susceptible to the pathogen populationelominateel by a variant of race 15 (effective genesSr67a222425262731 ineffective genes Sr8a8bge9a9g1011 13173037 elenominateel 15 (63) by Antonel1i 1969)In 1974 a new race (effective genes Sr8a8bge11 2224252627313 7 ineffective genes Sr67a9a9gl 0131730elenominateel II MeR in Argentina anel Gil in Brazil)viru1ent on most of the popular Argentinean (Antonelli 2000)Brazilian (Coelho 1980) anel Uruguayan cultivars (Luizzi et aI1980) causeel wielespreael epielemics uneler unusually favourableenvironmenta1 conelitions eluring 1975-1976

Wheat stem rust has not been severely epielemic for over 2elecaeles This was coincielent with the increaseel anel wielespreaeluse ofcultivars with lBL1RS (Sr31) (Antonelli 2000) During1975-2003 2 stem rust epielemics (1976 anel 1981) wereobserveel inPasso funelo RS Brazil (C ele Souza 2005 perscomm) Localised epielemir outbreaks occurred during the1990s on some wielely grown cultivars in Paraguay (ltapuacutea35) Brazil (CEP 14) anel Argentina (Victoria lNTA) Since2000 stem rust has been observeel sporaelically on highlysusceptible materiaIs in experimental fields throughout lheregion The release of stem rust susceptible cultivars suchas Klein Escorpioacuten Buck Yatasto anel the French cultivarBaguette 10 led to the reappearance ofthe clisease in c0111mercialfielels in northern Argentina in 2001 anel 2003 (1 Nisi 2005 perscomm)

The pathogen populationDuring 1949-199430 elifferentP graminis races were elescribeelin Brazil These combineel virulence on 4 to 14 SI genes (Sr5Sr6 Sr7a Sr8 Sr9a Sr9b Srge SI10 SI11 Sr12 SI13 Sr14Sr17 Sr29 Sr30 SI36 Sr37) Most olel races ielentifieel inArgentina anel Brazil were lost from the collections elue toreeluction in research on stem rust Few races have been founelsince 2000 One race (RTT-TR Brazilian elesignation 030)has been prevalent for many years in Brazil anel UruguaySince 2002 some changes in the pathogen population havebeen eletecteel in Brazil (A Barcellos C ele Souza S GermaacutenC Turra anel M Segalin 2003 unpublisheel elata) Argentinaanel Uruguay Genes Sr22 Sr24 Sr25 Sr26 Sr31 Sr32 Sr33Sr35 Sr39 anel Sr40 are currently effective across the regionSr27hael intermeeliate stem rust severity levels in Chile in 1984(Hacke 1986) Sr38 has not been testeel although CIMMYT lineMilan that may carry this gene has hael high fielel severity withsusceptible reaction to stem rust in Uruguay anel Paraguay ln2005 a very severe stem rust epidemic on international nurseriesfTom CIMMYT anel the Southern Cone region was observeel inSanta Cruz Bolivia

Breeding for resistance

Stem rust resistance was one of the major wheat breeelingobjectives when the elisease was important acrass the regionln some countries stem rust resistance was a requirement forcultivar release Sources of stem rust resistance were selecteelfrom the same international nurseries useel to select for leaf rustresistance During the 1950s anel 1960s sources of resistanceielentifieel in Argentina were Kenya 58 Kenya 117A EgyptNA 10 1 some lines from Egypt N95 Kenya Governor KenyaStanelarel (VaI lega 1940) Mayo 54 Kentana 51A Yaqui 53 anelnew resistance ielentifieel fram the lSWRN (Antonelli 2000)ln Brazil the best sources of resistance provieleel to breeelingprograms were Reel Egyptian Kenya 58 anel Kenya FarmerCultivars with resistance fram these sources became wielespreael(ela Silva 1966)

Sr22 Sr24 Sr25 Sr26 S27 Sr31 Sr32 Sr33 (Coelho 19821986) anel Sr2 (C Sousa pers comm) have been useel inEMBRAPA-CNPT ln the Brazilian company OR sources withslow rusting type of resistance are being useel

Presently the most important genes conferring resistance inthe regional germplasm are Sr31 anel Sr24 The presence of S31is inelicateel by the presence ofthe 1BLl RS translocation anelorthe presence of Lr26 The presence of Lr24 inelicates the presenceof Sr24 The introeluction anel use ofSr31 anel Sr24 in the regionalgermplasm were as elescribeel for the 1inkeel leaf rust resistancegenes Although it is not known if S24 anel Sr31 are presentsingly 01 in combination with other resistance genes the basisof resistance in the regional germplasm appears to be narrowGenes Sr5 S6 S7a Sr8a Sr8b Sr9b Sr 10 S111 anel Sr30 areprobably present (but largely ineifective) in some Argentineancultivars (Antonelli 2000) APR genes such as S2 are presentin many Brazilian lines anel cultivars (C ele Souza 2005 persCOIllI11)

The absence ofthe elisease anel reeluceel pathogen variabilityhas elecreaseel the opportunities of selection for resistanceanel also the priority that breeeling programs have assigneel tothis characteristic As a result some susceptible cultivars havebeen recently releaseel inclueling some of European origino ltwas estimateel that gt20 of the regional vheat area in 2004was sown to cultivars known to be susceptib1e to stem rust(Table 1) anel this area continues to increase The increasingarea of susceptible cultivars 1ll)Y result not on1y in inoculumbuilel-up anel higher infections on these cultivars but also toan increaseel likelihooel of eleveloping new virulent races oncurrently resistant cultivars ln aelelition the introeluction ofraces with S24 virulence from South Africa 01 lnelia coulelcause significant losses Because the 1BL1 RS translocation ispresent in a high praportion of the regional germplasm (gt 50of the wheat area is sown with cultivars with this translocationTable 1) the possibility of introeluction of the Sr31 virulentrace Ug99 from Africa is of concern (Antouelli 2000 Germuacutenet aI 2005 1 Ramirez 2005 pers comm) This coulel resultin significant epielemics since elata obtaineel in Kenya eluring2005 inelicateel that the large majority of a group of 72 currentregional cultivars are sqsceptible 01 moelerately susceptible(R Wanyera 2005 pers comm) Given this situation stem rustmay increase in importance in the near future anel it is urgent toincrease testing for resistance to this elisease The introeluction

of resistance genes effective against races virulent on lineswith Sr31 anel Sr24 as well as other effective genes notpresent in the regional germplasm shoulel be emphasiseel(Germaacuten et alo 2005)

The control of wheat rusts continues to be a challengefor breeelers anel rust pathologists in the Southern Cone ofSouth America Breeeling wheat cultivars with effective anelmore elurable resistance is being aelelresseel using traelitionalmethoelologies as well as graelually introelucing newer tools tohelp increase know1eelge about rust resistance anel its efficientuse in breeeling

We appreciate the contribution of Dr Ricardo Madariaga INIA-Chile andDr Robert Mclntosh University of Sydney for reviewing the paper Muchoflhe information from 1999-2004 was obtained eluring the execution ofaproject funded by USDA Funeling ofthe attendance ofthe main author to thecon[erence Global Landscapes in Cereal Rust Control (September 2005)by GRDC is greatly appreciated

Aguayo L (1983) Mejoramiento ele trigos invernales y primaverales enIa zona centro-slU ele Chile In Relmiatildeo ele Melhoristas de Trigo doCone Sul EMBRAPA-CNPT Passo Fundo RS (Coord O de S Rosa)pp 91-100 Diaacutelogo No 9 (Programa Cooperativo dePesquisaAgricolaMontevieleo)

Anelrade Vilaro O (J 990) Polvillo estriado o roya amarilla (Puecilliastriiforlllis Westenel) deI trigo en Ia zona sur de Chile Institutoele Investigaciones Agropecuarias Estacioacuten Experimental CarillancaBoletiacuten Teacutecnico No 164 Temuco

Antonelli EF (1969) Fuentesde germoplasma ele resistencia a enfermeeladesy plagasln Simposio deI trigo Buenos Aires pp 332-351 (AcademiaNacional de AgronomIacutea y Veterinaria Buenos Aires)

Antonelli EF (1982) Especializacion fisioloacutegica ele Pueeillia reeonditatritiei y p gralllillis tritiei en Ia Argentina en el periacuteodo1978-1981 In Reunioacuten de Especialistas en Royas dei Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBID)

Antonelli EF (1983) Principales patoacutegenos que afectan Ia produccioacuten de trigoen Ia Argentina In Simposio sobre Fitomejoramiento y Produccioacuten eleCereales INTNCIMMYT Marcos Juaacuterez Coacutereloba [sp] (AgenciaEstadounidense para el Desarrollo Internacional Universielad Estatal deOregon)

Antonelli EF (1986) Especializacioacuten fisioloacutegica ele PlIeeillia recollditatritici y P gralllinis tritiei en Ia Argentina en el periacuteodo 1982-1984In Reuniatildeo ele Especialistas em Ferrugens de Cereais de InvernoCNPTErvtBRAPA Passo Funelo RS (Ed CJ Mofestina) pp 37-39Diaacutelogo No 13 (PROCISUR Montevideo)

Antonelli EF (1994) Resistencia en plaacutentula y planta adulta decultivares comerciales argentinos ele trigo y progenitores (antecesores)tradicionales In [nteraccioacuten hospedante-patoacutegeno en hongos biotrofosInforme correspondiente aI afio 1993 [sp] (Instituto ele Geneacutetica EAFavret Castelar)

Antonclli EF (2000) La roya negra dei tallo (PlIceilia gra111illisf sp tritiei)Una ilustre ausente de los campos de trigo (Por cuill1to tiempo mils bull(Grafos Necochea Argentina)

Antonelli EF (2003) La roya anaranjaela (PlIceinia triticillCl Erikss) SobreIa efiacutemera resistencia observada en Ia uacuteltima eleacutecada en cultivarescomerciales ele trigo ele amplia difusioacuten en Ia Argentina (GrafosNecochea Argentina)

Barcellos AL (1982) As ferrugens do trigo no Brasil In Trigo no Brasil(Coorel EA Osoacuterio) pp 377-419 (Flll1dacatildeo Cargill Campinas)

Barcellos AL (1986) Ferrugem da folha do trigo no Brasil Populaccedilatildeopatogecircnica fontes de resistecircncia trigos comerciais perpetuaccedilatildeo econtrole quiacutemico [n Reuniatildeo de Especialistas em Ferrugens de Cereaisde Inverno CNPTEMBRAPA Passo Flmdo RS (Ed CJ Molestina)pp 72-87 Diaacutelogo No 13 (PROC1SUR Montevideo)

Barcellos AL (1991) Dmable leaf rust resistance in wheat in BrazilIn Wheat for the non-traditional warm areas (Ed D Saunders)pp462-465 (C1lIMYT Meacutexico DF)

Barcellos AL (2000) Urgent need for less ephemeral resistance to leaf rustin Brazilian wheat cultivars In 6th International Wheat ConferenceAgricultural Research [nstitute of the 1-LmgarianAcadel11Yof SciencesMartonvaacutesaacuter Hungary

Barcellos AL Aita L (1982) Siacutentese dos resultados das pesquisas sobreferrugem da folha do trigo realizadas no CNPT-EM BRPA Passo FundoRS Brasil de 1980 a 1982 In Reunioacuten de Especialistas en Royasdei Trigo Cono Sur de Ameacuterica INTA Castelar Argentina [sp](Programa IICA-Cono SmBlD)

Barcellos AL Aita L Coehlo ET (1982) Informaccedilotildees preliminares sobrefonte de inoacuteculo de ferrugem da folha e do colmo do trigo em PassoFundo [n Reunioacuten de Especialistas en Royas dcl Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBlD)

Barcellos AL Kohli MM (2003) Resultados da XI XII XlII e XIVcoleccedilatildeo para avaliaccedilatildeo e coleta de ferrugem do colmo e ferrugem dafolha do trigo 1998-2001 EMBRAPA TrigoC[MMYT Documentosno 37 Passo Fundo

Barcellos AL Roelfs AP de Moraes-Fernandes MIB (2000) Inheritance ofadult plant leaf rust resistance in the Brazilian wheat cultivar ToropiPan Disease 84 90-93

l3arcellos AL Tmra C (2004) Search for durable resistance to wheat leafrust in Brazil 1n Abstracts [ofthe] li th International Cereal Rusts andPowdery Mildews Conference Jolm lImes Centre Norwich EnglandUK p A23

Barcellos AL Turra C (2005) Partial resistance - best approach forcontrol of wheat leaf rust in envirolUnents favorable for the diseaseIn Wheat production in stressed envirolUnents abstracts of oral andposter presentations [of the] 7th 1nternational Vheat ConferenceMar dei Pbta Argentina pp 125 (Secretariat of Agriculture AnimalHusbandry Fisheries and Food)

BeckmaJm [(1940) EI problema dei trigo en el Brasil Revisla de a Faculadde AgronollIa (Monevideo) 19 21-36

Betucci L Ferreira V Szpiniak B (1971) Razas fisioloacutegicas ele Pucciniagrallinis Iriliei y Puccinia recondila Iriliei presentes en el Uruguay en1968 Universidael ele Ia Repuacuteblica Boletiacuten N~ 117 Montevideo

van Beuningen LT Kohli MM (1986) Resu1ts from the observalions onthe Latin Al11erican Rust Nursery (ELAR 1981-1983) In Reuniatildeo deEspecialistas em Ferrugens de Cereais de lI1Verno CNPTEMBRAPAPasso Funelo RS (Ed CJ Molestina) pp 7-20 Diaacutelogo No 13(PROC1SUR Montevieleo)

Boasso CS Levine MN (1951) Leaf rust of wheat Puccinia rubigoveraIriliei in Uruguay Phylopalhg) 41 736-741

Boerger A (1934) Consieleraeiones restropectivas acerca de Ia primeraaparieioacuten epieleacutemica ele Ia roya amarilla (Puceinia gullarull (Schm)Erikss et HeJU1)en el Riacuteo ele Ia Plata Revisla del Minislerio de [nduslrlas(Monlevideo) 15-16

Brammer SP Fernaneles MIB Barcellos AL Milach SCK (2004) Geneticanalysis of adult-plant resistanee to leaf rust in a elouble haploid wheat(Triliculll aeslivulll L em Thell) population Genelics and MoecuarBigy 27432-436 eloi I01590S 1415-47572004000300020

Bral11mer SP Worland A Bareellos AL Fernandez MIB (1998) lVlonosomieanalysis of adult-plant resistance to leaf rust in the BraziJian wheatcultivar Toropiacute 1n Proceeelings 9th International Wheat GeneticsSymposium Saskatoon Saskatchewan (Eel AE Slinkarel) v2pp 17-18 (University of Saskatchewan)

Campos PE Loacutepez JR Brach AM (2005) Characterization ofpopulation ofPuccinia Irilieina in Argentina in 2003 anel 2004 In Wheat proeluctionin stresseel envirornllents Abstracts of oral anel posteI presentationsof the 7th International Wheat Conference Mar elel Plata Argentinap I29 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Chaves MS Barcellos AL Germaacuten S Scheeren PL Dei Duca LeleJASilva M Soacute e Caieratildeo E (2005) Population elynamics of PlIccilialriticilain the South Cone region of South America In Wheat proeluction instresseel envirornllents Abstraets of oral anel poster presentations [ofthe] 7th International Wheat Conference Mar elel Plata Argentinap 130 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Coelho ET (1980) Distritribuccedilatildeo prevaJencia de novas razas fisiologicasde PlIccilia gmlllinis tritici (ferrugem do colmo elo trigo) no Brasil ele1974 a 1978 [n Xl Reuniatildeo Nacional de Pcsquisa ele Trigo PortoAlegre RS Brasil v 2 pp 9-22 (EMBRAPA Centro Nacional elePesquisa ele Trigo Passo Funelo)

Coelho E (1982) Siacutentese elos resultaelos elas pesquisas sobre ferrugem docolmo do trigo realizaelas no Centro Nacional ele Pesquisa ele Trigo(CNPT) EMBRAPA Passo FIUlelORS Brasil 1980 e 1981 In Reunioacutenele Especialistas en Royas elel Trigo Cono Sur ele Ameacuterica INTACastelar Argentina [sp] (Programa IlCA-Cono SurBlD)

Coelho E (1986) Siacutentese elos estuelos com ferrugem elo colmo elo trigo-1982 a 1984 In Reuniatildeo de Especialistas em Ferrugens ele Cereaisele Inverno CNPTIEMBRAPA Passo Funelo RS (Eel CJ Molestina)pp 107-110 Diaacutelogo No 13 (PROCISUR Montevieleo)

Dyck PL (1989) The inheritance of leaf rust resistance in wheat cultivarsKenyon anel B Manantial Caladial JOllma of Pall Seielce 691113-1117

Dyck PL (199 j) Genetics of aelult plant leaf rust resistance in ChineseSpring and Sturely wheats Crop Scielce 24 309-311

Dyck PL Kerber ER (1977) lnheritance of leaf rust resistance in wheatcultivars Rafaela anel EAP 26127 anel chromosome location of Irl7Caladial JOllma ofGelelics ald Cytgy 19 355-358

Dyck PL Samborski DL (1968a) Genetics of resistance to leaf rust in theconunon wheat varieties Webster Loros Brevit Carina Malakoff anelCentenario Caladial JOllma ofGelelics ald Cytgy 107-17

Dyck PL Samborski DL (1968b) Host-parasite interactions involvingtwo genes for leaf rust resistance in wheat ln Proceeelings of theThirel IJlternational Wheat Genetics Symposium Canberra Australia(Eels KW Finlay KW Shepherd) pp 245-250 (Australian Acaelemy ofScience Canberra)

Dyck PL Samborski DL (1970) The genetics of two alleles for leaf rustresistance at the [r14 locus in wheat Caladial JOllma of Gelelicsald C)lgy 12 689-694

Dyck PL Samborski DL (1982) The inheritance of resistance to Puceiliarecoldila in a group of conU110n wheat cultivars Caladial JOllma ofGelelics ald CylOogy 24273-283

Dyck PL Samborski DL Anelerson RG (1966) lnheritance of adultplant-Ieaf rust resistance eleriveel from the conmlon wleat varietiesExchange anel Frontana Caladial JOtlma oGelelics ald Cygy 8665-671

rlOSTAT (2006) Core production data (online) (FAO Rome) Availableat httpfaostatfaoorglsite340elefaultaspx Verifieel July 2006

Germaacuten S Caffarel JC (1999) Roya estriaela ele trigo In Jornaela de Cultivosele Invierno INIA La Estanzuela Colonia Uruguay pp 25-32 SerieActivielaeles ele Difusioacuten No 188 La Estanzuela

Germaacuten S Diaz M Verges R Castro M (2005) Breeeling for resistance towheat rusts in a highly favourable envirolUllent for eliseases In Wheatproeluction in stresseel envir Imlents Abstracts of oral anel posterpresentations [of theJ 7th International Wheat Conference Marelel Plata Argentina pp 139 (Secretariat of Agriculture AnimalHusbanelry fisheries anel Fooel)

10w frequencies in Argentina These raccs caused importantepielemics on the wielely sown Brazilian cultivar BRS 49 anel theUruguayan cultivars Estanzuela Peloacuten 90 (Lr1 Lr17 Lr26 Lr34Germaacuten and Kolmer 1996) and INJA Mirlo MCD-1O20 wasimportant in North America during 2002 (Kolmer et ai 2004R Singh 2003 pers comm) perhaps inelicating the occurrcnceof intercontinental migration

Race MCP-IO with a characteristic intennediate infectiontype on TcLr16 anel MHP-IO are probably the same race Thisrace was found in high frequency in Argentina during 2002-2004 in Uruguay during 2003-2004 and in Paraguay eluring2003 The leaf rust epielemics causeel by MCPMHP-I O on theArgentinean cultivar Klein Don Enriquc (Lr26 anel aelelitionalresistance Antonelli 2003) planted on over 2 million ha werevery severe and widespread during 2002 anel 2003

Race MDR-IO20 first identified in 2003 overcame theresistance ofthe Uruguayan cultivars JNIA Torcaza (Lr1 OLr24Germaacuten et ai 2005) anel INIA Churrinche anel the widelygrawn Brazilian cultivar Ocircnix The freq I c ufthis race rapidlyincreased in Uruguay during 2004 allll in tlgcntina anel Brazilin 2005

Some important epielemics that occurreel on rcgional cultivarssince the 1990s due to the spread of nces wirh new virulencecombinations were elescribed by Ant(nelli (2003) and Germaacutenet ai (2004)

Virulence has frequently elevelo)cd for effective resistancegenes eleployed in coml11ercial cultivlrs in the Southern ConeVirulence on wheats with Lr]6 8 1irst detected in Argentinain 1980 (Antonelli 2003) anel in il m 1982 (Barcellos 1986)Many CIMMYT lines anel dtiaiivc~ releaseel in the rcgion(Kohli anel Skovmanel 1997) became ~usceptible due to raceswith Lr26 virulence Virulence for Lr2middot first deteeted in 1981both in Argentina (Antonelli 1982) anci Brazil (Barcellos andAita 1982) caused extrell1ely severe epil emics durillg 1982 onthe Argentinean cultivar Cargill Trigal 8( 1 and on the cultivarTifton grown in Brazil Virulence for 1 --9 first detected inArgentina in 1982 (Antonelli 1986) causcl1 a major epidemicduring 1985 on the Argentinean cultivar La 1OzINTA grown inArgentina and Uruguay (Germaacuten et ai 1986) Virulence forLr3 7was first elemonstratecl in Uruguay in 1999 in race MCD-l 020which affected several cultivars that elonot carry LI 37 Virulenceon Lr19 was first observecl in 2004 in Paraguay (de Vieclll1a et ai

2(05) and Argentina where itwas verifiecl by E Antonelli (2005pers comm) During 2005 the Argentinean cultivar Pr01NTAGaucho which probably has Lri9 was severely affected by leafrust

Breeding for resistance

During the first period of wheat breeding in the rcgion leaf rustresistance was mainly clerived from locally adapted germplasmwhich in many cases was also used by breeding programs inother countries The Brazilian cultivar Frontana (Lri3 Lr34LrT3 and aelditional aelult plant resistance Dyck et ai 1966Dyck anel Samborski 1982 Singh and Rajarall1 1992) anel theArgentincan cultivar Buck Manantial (Lda or an allele Lri6and Lr17a Lri3 anel possibly Lr34 Dyek 1989) are sources ofelurable resistance that have bcen useel internationally Sourcesof resistance were selecteel from germplasm elistribulcel by

USDA since the 1950s and by the Rockefeller Foundation (IaterCJMMYT) since the 1960s Many CIMMYT 1ines elerived leafrust resistance from South American germplasm (Rajaram et aI1988)

Seeelling resistance genes present in the regional germplasmelevelopeel before 1960 areLr1 Lr3a Lrlbg Ldka Lri1 Lri4bLri6 anel Lr17a (Dyck and Samborski 1968a 1968b 1970Haggag anel Dyck 1973 Dyck andKerber 1977 Antonelli 1983Roelfs 1988 Dyck 1989 Kolmer et ai 2007 E F Antonelli2005 unpublished data) Two previously undesignated seeellingresislance genes temporari1y designated Lr7D anel Lr44d(originally present in the Argentinean cultivar Barletta 7Danel the Uruguayan cultivar Americano 44d respectively) weredescribecl by Antonelli (1994) Kolmer et ai (2007) founel apreviously unidelltified gene in Americano 25e

Aclult plant resistanee genes Lr12 Lr13 and Lr34 are alsopresent in the traditional gcrmplasm (Dyck el ai 1966 Dyck andSamborski 1982 Roelfs 1988 Dyck 1989 Singh and Rajaram1992 Kolmer et ai 2007) Brazilian cultivar BH 1146 hasLr13 and Ld4 (Kolmcr and Liu 20(1) Uneler the extremelyfavourab1e eonditions for leaf rust clevelopment present in theregion Lr34 and other APR genes were probably selected fromthe heterogeneous landrace cultivars and then mintained innewer cultivars Singh and Rajaram (1992) claimed evielencefor APR genes adelitional to LI13 anel Lr34 in frontana Kolmeret ai (2007) found one APR gene different from Lri2 LI 13 orLr34 in Americano 25e and 2 possibly unique A10R genes inAmericano 26n

More recently releasecl eultivars in South America havebeen clerivecl fram germplasm obtainecl from CIMMYT andother breeding programs Seedling resistance genes LI 10Lr14a Lr19 Lr23 Lr26 Lr27 and Ld1 (Singh andRajaram 1991 Singh 1993) may have been introduced VithCIMMYT germplasm Lr26 is probably the most widelydistributed of these genes since it is present in many high-yielcling CIMMYT lines (eg Veery Bobwhite Alondra Kauzand others) and clerivatives that have been used directlyas cultivars or in local crosses In Chile Lr26 was alsointroeluced through direct use of European wheats carryingthe 1BLI RS translocation (eg Aurora Kavkaz BezostayaLovrin Mildress Clement 1 Ramirez pers comm) Lr9 ispresent in Precoz Paranaacute INTA and its derivative La PazINTA (Antonelli 1983) Lr24 is present in Cargill Trigal800 (Antonelli 2003) and other Agent derivatives useel inbreeding programs in Argentina anel Uruguay anel in AmigoTi fton and Century useel in Brazil (Barcellos 1991 cited byZolelan and Barcellos 2002 The et ai 1991 McIntosh et ai1995) Lr34 and othcr APR genes conferring durable resistanceare wielely clistributed in CIMMYT gcrmplasm (Singh anelRajaram 1992 Singh and Huerta-Espino 1995) mostly clerivedfrom lraditional Southern Cone germplasm and in currentregional cultivars

Resistance genes LI 10 Lr23 Lr24 anel Lr26 most commonin Brazilian germplasm testeel during 1996-97 (Zoldan andBarcellos 2(02) continucd to be present in the most importantcultivars used in 2004 Lri3 and Lr34 are also widely presentin the Brazilian germplasm (Zoldan et ai 2000 de Sousa andBarcellos 2000 2001) together with other APR genes suchas Trpl anel Trp2 (temporary designatiol1) present il1 Toropiacute

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epielemics in most of the region (from Chile to Rio Graneleelo Sul in Brazil) causing extremely high losses in theeastern epielemio10gical zone (Boerger 1934 Vallega 1938)The presence in Argentina anel Uruguay of COl11l11onracesfounel in Chile (Straib 1937) inelicates stripe rust probablymigrateel through the Aneles liom Chile to the easteru part ofthe continent

Yr18 anel tightly linkeel Lr34 (McIntosh 1992 Singh1992) were probably present in tolerant wheat lines selecteeluneler the extreme 1929 anel 1930 stripe rust epielel11ics assuggesteel by Dyck (1991) anel Kolmer (1996) The Brazil iancultivar Fronteira one of Frontanas parents selecteel at BageacuteExperimental Station anel releaseel in 1934 was highly resistantto stripe rust (Beckmann 1940) ln Argentina cv Chino alsoknown as Chinese 166 expresseel the most effective resistanceanel was useel in crosses from which aelapteel resistant lines wereeleriveel (Val1ega 1938)

Unlike other regions of the worlel where the importanceof stripe rust is increasing no other wielespreael epielemichas occurreel in the eastern epielemiological zone anel theelisease is currently not economically important ln the southernwheat arca of Argentina only sporaelic localiseel outbreakshave been observeel on highly susceptible cultivars Similarloca1iseel epielemics have also been observeel in southern Brazilaifecting cv Curitiba eluring 1968 (Schraml11 1969) anel cvTifton eluring 1980 ln 1998 a moelerate epielemic ofstripe rustoccurreel in Uruguay (Germaacuten anel Caifare1 1999) During thisepielemic some cultivars with the lBLIRS translocation suchas Estanzuela Carelenal (Veery 3) were susceptible inelicatingthe presence ofvirulence on Yr9 Many cultivars known to carryYr18Lr34 hael 10w to intermeeliate stripe rust severities

Puccinia slriiformis probab1y oversummers in the valleys ofthe Argentinean Aneles (Neuqueacuten anel Rio Negro provinces)on wheat anel wilel Hordeum spp (Vallega anel Favret 1947)elelaying the elispersal ofinoculum to the major proeluction areasin the north Most germp1asl11 from Argentina Brazil Paraguayanel Urllguay is moelerately susceptible or susceptible uneler theheavy elisease conelitions present in Chile The absence ofearlyinfections even in the presence ofsusceptible cllltivars inelicatesthat inoculum is usually not present at early stages of cropelevelopment anel that oversummering does not regularly OCCllrin the l11ain wheat areas Uneler these conelitions avoieling theuse of highly susceptible cultivars anel maintaining resistancelevels such as those conferreel by Yr18 or other genes withsimilar eiacuteTect appears to be an effective strategy to prcvcntstripe rust epielemics in Uruguay (Germaacuten anel Caffarel 1999)anel the rest of the eastem epielemiologic zanc ln aelelitionthe increaseel use of durable APR to leaf rust often associatedwith APR to stripe rust (Singh 1992 Singh anel Rajaram 1994Singh el ai 2003) will also increase the leveI of resistance tostripe rust

Wheat stem rustOistribution and occurrenceAlthough the incielence of steni rust historically has been moresporaelic than that ofleafrust it causeel higher 1evels of elamageeluring severe epielemics It was consielereelthe most elestructivewheat rust in Brazil (ela Silva 1966) Paraguay (ele Vieelma anel

Bozzano 1986) Uruguay (Ribeiro 1952) the northem wheatgrowing area ofChile (Hacke 1990) anel the northern anel central-north wheat area of Argentina (Val1ega anel Favret 1952)

Oversummering of stem rust has been observeel on volunteerwheat anel barley plants in Uruguay anel in the south of BuenosAires province (Argentina) where it is frequently present in lhesummer nursery at Balcarce (1 Nisi 2005 pers comm) Stemrust also oversuml11ers locally in Brazil (Barcellos et ai 1982)

A very severe stem rust epielemic occurreel in Argentinaanel other Southern Cone countries in 1950 (Antonelli2000) The majority of commercia1 cultivars from regionalbreeeling programs were susceptible to the pathogen populationelominateel by a variant of race 15 (effective genesSr67a222425262731 ineffective genes Sr8a8bge9a9g1011 13173037 elenominateel 15 (63) by Antonel1i 1969)In 1974 a new race (effective genes Sr8a8bge11 2224252627313 7 ineffective genes Sr67a9a9gl 0131730elenominateel II MeR in Argentina anel Gil in Brazil)viru1ent on most of the popular Argentinean (Antonelli 2000)Brazilian (Coelho 1980) anel Uruguayan cultivars (Luizzi et aI1980) causeel wielespreael epielemics uneler unusually favourableenvironmenta1 conelitions eluring 1975-1976

Wheat stem rust has not been severely epielemic for over 2elecaeles This was coincielent with the increaseel anel wielespreaeluse ofcultivars with lBL1RS (Sr31) (Antonelli 2000) During1975-2003 2 stem rust epielemics (1976 anel 1981) wereobserveel inPasso funelo RS Brazil (C ele Souza 2005 perscomm) Localised epielemir outbreaks occurred during the1990s on some wielely grown cultivars in Paraguay (ltapuacutea35) Brazil (CEP 14) anel Argentina (Victoria lNTA) Since2000 stem rust has been observeel sporaelically on highlysusceptible materiaIs in experimental fields throughout lheregion The release of stem rust susceptible cultivars suchas Klein Escorpioacuten Buck Yatasto anel the French cultivarBaguette 10 led to the reappearance ofthe clisease in c0111mercialfielels in northern Argentina in 2001 anel 2003 (1 Nisi 2005 perscomm)

The pathogen populationDuring 1949-199430 elifferentP graminis races were elescribeelin Brazil These combineel virulence on 4 to 14 SI genes (Sr5Sr6 Sr7a Sr8 Sr9a Sr9b Srge SI10 SI11 Sr12 SI13 Sr14Sr17 Sr29 Sr30 SI36 Sr37) Most olel races ielentifieel inArgentina anel Brazil were lost from the collections elue toreeluction in research on stem rust Few races have been founelsince 2000 One race (RTT-TR Brazilian elesignation 030)has been prevalent for many years in Brazil anel UruguaySince 2002 some changes in the pathogen population havebeen eletecteel in Brazil (A Barcellos C ele Souza S GermaacutenC Turra anel M Segalin 2003 unpublisheel elata) Argentinaanel Uruguay Genes Sr22 Sr24 Sr25 Sr26 Sr31 Sr32 Sr33Sr35 Sr39 anel Sr40 are currently effective across the regionSr27hael intermeeliate stem rust severity levels in Chile in 1984(Hacke 1986) Sr38 has not been testeel although CIMMYT lineMilan that may carry this gene has hael high fielel severity withsusceptible reaction to stem rust in Uruguay anel Paraguay ln2005 a very severe stem rust epidemic on international nurseriesfTom CIMMYT anel the Southern Cone region was observeel inSanta Cruz Bolivia

Breeding for resistance

Stem rust resistance was one of the major wheat breeelingobjectives when the elisease was important acrass the regionln some countries stem rust resistance was a requirement forcultivar release Sources of stem rust resistance were selecteelfrom the same international nurseries useel to select for leaf rustresistance During the 1950s anel 1960s sources of resistanceielentifieel in Argentina were Kenya 58 Kenya 117A EgyptNA 10 1 some lines from Egypt N95 Kenya Governor KenyaStanelarel (VaI lega 1940) Mayo 54 Kentana 51A Yaqui 53 anelnew resistance ielentifieel fram the lSWRN (Antonelli 2000)ln Brazil the best sources of resistance provieleel to breeelingprograms were Reel Egyptian Kenya 58 anel Kenya FarmerCultivars with resistance fram these sources became wielespreael(ela Silva 1966)

Sr22 Sr24 Sr25 Sr26 S27 Sr31 Sr32 Sr33 (Coelho 19821986) anel Sr2 (C Sousa pers comm) have been useel inEMBRAPA-CNPT ln the Brazilian company OR sources withslow rusting type of resistance are being useel

Presently the most important genes conferring resistance inthe regional germplasm are Sr31 anel Sr24 The presence of S31is inelicateel by the presence ofthe 1BLl RS translocation anelorthe presence of Lr26 The presence of Lr24 inelicates the presenceof Sr24 The introeluction anel use ofSr31 anel Sr24 in the regionalgermplasm were as elescribeel for the 1inkeel leaf rust resistancegenes Although it is not known if S24 anel Sr31 are presentsingly 01 in combination with other resistance genes the basisof resistance in the regional germplasm appears to be narrowGenes Sr5 S6 S7a Sr8a Sr8b Sr9b Sr 10 S111 anel Sr30 areprobably present (but largely ineifective) in some Argentineancultivars (Antonelli 2000) APR genes such as S2 are presentin many Brazilian lines anel cultivars (C ele Souza 2005 persCOIllI11)

The absence ofthe elisease anel reeluceel pathogen variabilityhas elecreaseel the opportunities of selection for resistanceanel also the priority that breeeling programs have assigneel tothis characteristic As a result some susceptible cultivars havebeen recently releaseel inclueling some of European origino ltwas estimateel that gt20 of the regional vheat area in 2004was sown to cultivars known to be susceptib1e to stem rust(Table 1) anel this area continues to increase The increasingarea of susceptible cultivars 1ll)Y result not on1y in inoculumbuilel-up anel higher infections on these cultivars but also toan increaseel likelihooel of eleveloping new virulent races oncurrently resistant cultivars ln aelelition the introeluction ofraces with S24 virulence from South Africa 01 lnelia coulelcause significant losses Because the 1BL1 RS translocation ispresent in a high praportion of the regional germplasm (gt 50of the wheat area is sown with cultivars with this translocationTable 1) the possibility of introeluction of the Sr31 virulentrace Ug99 from Africa is of concern (Antouelli 2000 Germuacutenet aI 2005 1 Ramirez 2005 pers comm) This coulel resultin significant epielemics since elata obtaineel in Kenya eluring2005 inelicateel that the large majority of a group of 72 currentregional cultivars are sqsceptible 01 moelerately susceptible(R Wanyera 2005 pers comm) Given this situation stem rustmay increase in importance in the near future anel it is urgent toincrease testing for resistance to this elisease The introeluction

of resistance genes effective against races virulent on lineswith Sr31 anel Sr24 as well as other effective genes notpresent in the regional germplasm shoulel be emphasiseel(Germaacuten et alo 2005)

The control of wheat rusts continues to be a challengefor breeelers anel rust pathologists in the Southern Cone ofSouth America Breeeling wheat cultivars with effective anelmore elurable resistance is being aelelresseel using traelitionalmethoelologies as well as graelually introelucing newer tools tohelp increase know1eelge about rust resistance anel its efficientuse in breeeling

We appreciate the contribution of Dr Ricardo Madariaga INIA-Chile andDr Robert Mclntosh University of Sydney for reviewing the paper Muchoflhe information from 1999-2004 was obtained eluring the execution ofaproject funded by USDA Funeling ofthe attendance ofthe main author to thecon[erence Global Landscapes in Cereal Rust Control (September 2005)by GRDC is greatly appreciated

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Barcellos AL (2000) Urgent need for less ephemeral resistance to leaf rustin Brazilian wheat cultivars In 6th International Wheat ConferenceAgricultural Research [nstitute of the 1-LmgarianAcadel11Yof SciencesMartonvaacutesaacuter Hungary

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Barcellos AL Aita L Coehlo ET (1982) Informaccedilotildees preliminares sobrefonte de inoacuteculo de ferrugem da folha e do colmo do trigo em PassoFundo [n Reunioacuten de Especialistas en Royas dcl Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBlD)

Barcellos AL Kohli MM (2003) Resultados da XI XII XlII e XIVcoleccedilatildeo para avaliaccedilatildeo e coleta de ferrugem do colmo e ferrugem dafolha do trigo 1998-2001 EMBRAPA TrigoC[MMYT Documentosno 37 Passo Fundo

Barcellos AL Roelfs AP de Moraes-Fernandes MIB (2000) Inheritance ofadult plant leaf rust resistance in the Brazilian wheat cultivar ToropiPan Disease 84 90-93

l3arcellos AL Tmra C (2004) Search for durable resistance to wheat leafrust in Brazil 1n Abstracts [ofthe] li th International Cereal Rusts andPowdery Mildews Conference Jolm lImes Centre Norwich EnglandUK p A23

Barcellos AL Turra C (2005) Partial resistance - best approach forcontrol of wheat leaf rust in envirolUnents favorable for the diseaseIn Wheat production in stressed envirolUnents abstracts of oral andposter presentations [of the] 7th 1nternational Vheat ConferenceMar dei Pbta Argentina pp 125 (Secretariat of Agriculture AnimalHusbandry Fisheries and Food)

BeckmaJm [(1940) EI problema dei trigo en el Brasil Revisla de a Faculadde AgronollIa (Monevideo) 19 21-36

Betucci L Ferreira V Szpiniak B (1971) Razas fisioloacutegicas ele Pucciniagrallinis Iriliei y Puccinia recondila Iriliei presentes en el Uruguay en1968 Universidael ele Ia Repuacuteblica Boletiacuten N~ 117 Montevideo

van Beuningen LT Kohli MM (1986) Resu1ts from the observalions onthe Latin Al11erican Rust Nursery (ELAR 1981-1983) In Reuniatildeo deEspecialistas em Ferrugens de Cereais de lI1Verno CNPTEMBRAPAPasso Funelo RS (Ed CJ Molestina) pp 7-20 Diaacutelogo No 13(PROC1SUR Montevieleo)

Boasso CS Levine MN (1951) Leaf rust of wheat Puccinia rubigoveraIriliei in Uruguay Phylopalhg) 41 736-741

Boerger A (1934) Consieleraeiones restropectivas acerca de Ia primeraaparieioacuten epieleacutemica ele Ia roya amarilla (Puceinia gullarull (Schm)Erikss et HeJU1)en el Riacuteo ele Ia Plata Revisla del Minislerio de [nduslrlas(Monlevideo) 15-16

Brammer SP Fernaneles MIB Barcellos AL Milach SCK (2004) Geneticanalysis of adult-plant resistanee to leaf rust in a elouble haploid wheat(Triliculll aeslivulll L em Thell) population Genelics and MoecuarBigy 27432-436 eloi I01590S 1415-47572004000300020

Bral11mer SP Worland A Bareellos AL Fernandez MIB (1998) lVlonosomieanalysis of adult-plant resistance to leaf rust in the BraziJian wheatcultivar Toropiacute 1n Proceeelings 9th International Wheat GeneticsSymposium Saskatoon Saskatchewan (Eel AE Slinkarel) v2pp 17-18 (University of Saskatchewan)

Campos PE Loacutepez JR Brach AM (2005) Characterization ofpopulation ofPuccinia Irilieina in Argentina in 2003 anel 2004 In Wheat proeluctionin stresseel envirornllents Abstracts of oral anel posteI presentationsof the 7th International Wheat Conference Mar elel Plata Argentinap I29 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Chaves MS Barcellos AL Germaacuten S Scheeren PL Dei Duca LeleJASilva M Soacute e Caieratildeo E (2005) Population elynamics of PlIccilialriticilain the South Cone region of South America In Wheat proeluction instresseel envirornllents Abstraets of oral anel poster presentations [ofthe] 7th International Wheat Conference Mar elel Plata Argentinap 130 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Coelho ET (1980) Distritribuccedilatildeo prevaJencia de novas razas fisiologicasde PlIccilia gmlllinis tritici (ferrugem do colmo elo trigo) no Brasil ele1974 a 1978 [n Xl Reuniatildeo Nacional de Pcsquisa ele Trigo PortoAlegre RS Brasil v 2 pp 9-22 (EMBRAPA Centro Nacional elePesquisa ele Trigo Passo Funelo)

Coelho E (1982) Siacutentese elos resultaelos elas pesquisas sobre ferrugem docolmo do trigo realizaelas no Centro Nacional ele Pesquisa ele Trigo(CNPT) EMBRAPA Passo FIUlelORS Brasil 1980 e 1981 In Reunioacutenele Especialistas en Royas elel Trigo Cono Sur ele Ameacuterica INTACastelar Argentina [sp] (Programa IlCA-Cono SurBlD)

Coelho E (1986) Siacutentese elos estuelos com ferrugem elo colmo elo trigo-1982 a 1984 In Reuniatildeo de Especialistas em Ferrugens ele Cereaisele Inverno CNPTIEMBRAPA Passo Funelo RS (Eel CJ Molestina)pp 107-110 Diaacutelogo No 13 (PROCISUR Montevieleo)

Dyck PL (1989) The inheritance of leaf rust resistance in wheat cultivarsKenyon anel B Manantial Caladial JOllma of Pall Seielce 691113-1117

Dyck PL (199 j) Genetics of aelult plant leaf rust resistance in ChineseSpring and Sturely wheats Crop Scielce 24 309-311

Dyck PL Kerber ER (1977) lnheritance of leaf rust resistance in wheatcultivars Rafaela anel EAP 26127 anel chromosome location of Irl7Caladial JOllma ofGelelics ald Cytgy 19 355-358

Dyck PL Samborski DL (1968a) Genetics of resistance to leaf rust in theconunon wheat varieties Webster Loros Brevit Carina Malakoff anelCentenario Caladial JOllma ofGelelics ald Cytgy 107-17

Dyck PL Samborski DL (1968b) Host-parasite interactions involvingtwo genes for leaf rust resistance in wheat ln Proceeelings of theThirel IJlternational Wheat Genetics Symposium Canberra Australia(Eels KW Finlay KW Shepherd) pp 245-250 (Australian Acaelemy ofScience Canberra)

Dyck PL Samborski DL (1970) The genetics of two alleles for leaf rustresistance at the [r14 locus in wheat Caladial JOllma of Gelelicsald C)lgy 12 689-694

Dyck PL Samborski DL (1982) The inheritance of resistance to Puceiliarecoldila in a group of conU110n wheat cultivars Caladial JOllma ofGelelics ald CylOogy 24273-283

Dyck PL Samborski DL Anelerson RG (1966) lnheritance of adultplant-Ieaf rust resistance eleriveel from the conmlon wleat varietiesExchange anel Frontana Caladial JOtlma oGelelics ald Cygy 8665-671

rlOSTAT (2006) Core production data (online) (FAO Rome) Availableat httpfaostatfaoorglsite340elefaultaspx Verifieel July 2006

Germaacuten S Caffarel JC (1999) Roya estriaela ele trigo In Jornaela de Cultivosele Invierno INIA La Estanzuela Colonia Uruguay pp 25-32 SerieActivielaeles ele Difusioacuten No 188 La Estanzuela

Germaacuten S Diaz M Verges R Castro M (2005) Breeeling for resistance towheat rusts in a highly favourable envirolUllent for eliseases In Wheatproeluction in stresseel envir Imlents Abstracts of oral anel posterpresentations [of theJ 7th International Wheat Conference Marelel Plata Argentina pp 139 (Secretariat of Agriculture AnimalHusbanelry fisheries anel Fooel)

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epielemics in most of the region (from Chile to Rio Graneleelo Sul in Brazil) causing extremely high losses in theeastern epielemio10gical zone (Boerger 1934 Vallega 1938)The presence in Argentina anel Uruguay of COl11l11onracesfounel in Chile (Straib 1937) inelicates stripe rust probablymigrateel through the Aneles liom Chile to the easteru part ofthe continent

Yr18 anel tightly linkeel Lr34 (McIntosh 1992 Singh1992) were probably present in tolerant wheat lines selecteeluneler the extreme 1929 anel 1930 stripe rust epielel11ics assuggesteel by Dyck (1991) anel Kolmer (1996) The Brazil iancultivar Fronteira one of Frontanas parents selecteel at BageacuteExperimental Station anel releaseel in 1934 was highly resistantto stripe rust (Beckmann 1940) ln Argentina cv Chino alsoknown as Chinese 166 expresseel the most effective resistanceanel was useel in crosses from which aelapteel resistant lines wereeleriveel (Val1ega 1938)

Unlike other regions of the worlel where the importanceof stripe rust is increasing no other wielespreael epielemichas occurreel in the eastern epielemiological zone anel theelisease is currently not economically important ln the southernwheat arca of Argentina only sporaelic localiseel outbreakshave been observeel on highly susceptible cultivars Similarloca1iseel epielemics have also been observeel in southern Brazilaifecting cv Curitiba eluring 1968 (Schraml11 1969) anel cvTifton eluring 1980 ln 1998 a moelerate epielemic ofstripe rustoccurreel in Uruguay (Germaacuten anel Caifare1 1999) During thisepielemic some cultivars with the lBLIRS translocation suchas Estanzuela Carelenal (Veery 3) were susceptible inelicatingthe presence ofvirulence on Yr9 Many cultivars known to carryYr18Lr34 hael 10w to intermeeliate stripe rust severities

Puccinia slriiformis probab1y oversummers in the valleys ofthe Argentinean Aneles (Neuqueacuten anel Rio Negro provinces)on wheat anel wilel Hordeum spp (Vallega anel Favret 1947)elelaying the elispersal ofinoculum to the major proeluction areasin the north Most germp1asl11 from Argentina Brazil Paraguayanel Urllguay is moelerately susceptible or susceptible uneler theheavy elisease conelitions present in Chile The absence ofearlyinfections even in the presence ofsusceptible cllltivars inelicatesthat inoculum is usually not present at early stages of cropelevelopment anel that oversummering does not regularly OCCllrin the l11ain wheat areas Uneler these conelitions avoieling theuse of highly susceptible cultivars anel maintaining resistancelevels such as those conferreel by Yr18 or other genes withsimilar eiacuteTect appears to be an effective strategy to prcvcntstripe rust epielemics in Uruguay (Germaacuten anel Caffarel 1999)anel the rest of the eastem epielemiologic zanc ln aelelitionthe increaseel use of durable APR to leaf rust often associatedwith APR to stripe rust (Singh 1992 Singh anel Rajaram 1994Singh el ai 2003) will also increase the leveI of resistance tostripe rust

Wheat stem rustOistribution and occurrenceAlthough the incielence of steni rust historically has been moresporaelic than that ofleafrust it causeel higher 1evels of elamageeluring severe epielemics It was consielereelthe most elestructivewheat rust in Brazil (ela Silva 1966) Paraguay (ele Vieelma anel

Bozzano 1986) Uruguay (Ribeiro 1952) the northem wheatgrowing area ofChile (Hacke 1990) anel the northern anel central-north wheat area of Argentina (Val1ega anel Favret 1952)

Oversummering of stem rust has been observeel on volunteerwheat anel barley plants in Uruguay anel in the south of BuenosAires province (Argentina) where it is frequently present in lhesummer nursery at Balcarce (1 Nisi 2005 pers comm) Stemrust also oversuml11ers locally in Brazil (Barcellos et ai 1982)

A very severe stem rust epielemic occurreel in Argentinaanel other Southern Cone countries in 1950 (Antonelli2000) The majority of commercia1 cultivars from regionalbreeeling programs were susceptible to the pathogen populationelominateel by a variant of race 15 (effective genesSr67a222425262731 ineffective genes Sr8a8bge9a9g1011 13173037 elenominateel 15 (63) by Antonel1i 1969)In 1974 a new race (effective genes Sr8a8bge11 2224252627313 7 ineffective genes Sr67a9a9gl 0131730elenominateel II MeR in Argentina anel Gil in Brazil)viru1ent on most of the popular Argentinean (Antonelli 2000)Brazilian (Coelho 1980) anel Uruguayan cultivars (Luizzi et aI1980) causeel wielespreael epielemics uneler unusually favourableenvironmenta1 conelitions eluring 1975-1976

Wheat stem rust has not been severely epielemic for over 2elecaeles This was coincielent with the increaseel anel wielespreaeluse ofcultivars with lBL1RS (Sr31) (Antonelli 2000) During1975-2003 2 stem rust epielemics (1976 anel 1981) wereobserveel inPasso funelo RS Brazil (C ele Souza 2005 perscomm) Localised epielemir outbreaks occurred during the1990s on some wielely grown cultivars in Paraguay (ltapuacutea35) Brazil (CEP 14) anel Argentina (Victoria lNTA) Since2000 stem rust has been observeel sporaelically on highlysusceptible materiaIs in experimental fields throughout lheregion The release of stem rust susceptible cultivars suchas Klein Escorpioacuten Buck Yatasto anel the French cultivarBaguette 10 led to the reappearance ofthe clisease in c0111mercialfielels in northern Argentina in 2001 anel 2003 (1 Nisi 2005 perscomm)

The pathogen populationDuring 1949-199430 elifferentP graminis races were elescribeelin Brazil These combineel virulence on 4 to 14 SI genes (Sr5Sr6 Sr7a Sr8 Sr9a Sr9b Srge SI10 SI11 Sr12 SI13 Sr14Sr17 Sr29 Sr30 SI36 Sr37) Most olel races ielentifieel inArgentina anel Brazil were lost from the collections elue toreeluction in research on stem rust Few races have been founelsince 2000 One race (RTT-TR Brazilian elesignation 030)has been prevalent for many years in Brazil anel UruguaySince 2002 some changes in the pathogen population havebeen eletecteel in Brazil (A Barcellos C ele Souza S GermaacutenC Turra anel M Segalin 2003 unpublisheel elata) Argentinaanel Uruguay Genes Sr22 Sr24 Sr25 Sr26 Sr31 Sr32 Sr33Sr35 Sr39 anel Sr40 are currently effective across the regionSr27hael intermeeliate stem rust severity levels in Chile in 1984(Hacke 1986) Sr38 has not been testeel although CIMMYT lineMilan that may carry this gene has hael high fielel severity withsusceptible reaction to stem rust in Uruguay anel Paraguay ln2005 a very severe stem rust epidemic on international nurseriesfTom CIMMYT anel the Southern Cone region was observeel inSanta Cruz Bolivia

Breeding for resistance

Stem rust resistance was one of the major wheat breeelingobjectives when the elisease was important acrass the regionln some countries stem rust resistance was a requirement forcultivar release Sources of stem rust resistance were selecteelfrom the same international nurseries useel to select for leaf rustresistance During the 1950s anel 1960s sources of resistanceielentifieel in Argentina were Kenya 58 Kenya 117A EgyptNA 10 1 some lines from Egypt N95 Kenya Governor KenyaStanelarel (VaI lega 1940) Mayo 54 Kentana 51A Yaqui 53 anelnew resistance ielentifieel fram the lSWRN (Antonelli 2000)ln Brazil the best sources of resistance provieleel to breeelingprograms were Reel Egyptian Kenya 58 anel Kenya FarmerCultivars with resistance fram these sources became wielespreael(ela Silva 1966)

Sr22 Sr24 Sr25 Sr26 S27 Sr31 Sr32 Sr33 (Coelho 19821986) anel Sr2 (C Sousa pers comm) have been useel inEMBRAPA-CNPT ln the Brazilian company OR sources withslow rusting type of resistance are being useel

Presently the most important genes conferring resistance inthe regional germplasm are Sr31 anel Sr24 The presence of S31is inelicateel by the presence ofthe 1BLl RS translocation anelorthe presence of Lr26 The presence of Lr24 inelicates the presenceof Sr24 The introeluction anel use ofSr31 anel Sr24 in the regionalgermplasm were as elescribeel for the 1inkeel leaf rust resistancegenes Although it is not known if S24 anel Sr31 are presentsingly 01 in combination with other resistance genes the basisof resistance in the regional germplasm appears to be narrowGenes Sr5 S6 S7a Sr8a Sr8b Sr9b Sr 10 S111 anel Sr30 areprobably present (but largely ineifective) in some Argentineancultivars (Antonelli 2000) APR genes such as S2 are presentin many Brazilian lines anel cultivars (C ele Souza 2005 persCOIllI11)

The absence ofthe elisease anel reeluceel pathogen variabilityhas elecreaseel the opportunities of selection for resistanceanel also the priority that breeeling programs have assigneel tothis characteristic As a result some susceptible cultivars havebeen recently releaseel inclueling some of European origino ltwas estimateel that gt20 of the regional vheat area in 2004was sown to cultivars known to be susceptib1e to stem rust(Table 1) anel this area continues to increase The increasingarea of susceptible cultivars 1ll)Y result not on1y in inoculumbuilel-up anel higher infections on these cultivars but also toan increaseel likelihooel of eleveloping new virulent races oncurrently resistant cultivars ln aelelition the introeluction ofraces with S24 virulence from South Africa 01 lnelia coulelcause significant losses Because the 1BL1 RS translocation ispresent in a high praportion of the regional germplasm (gt 50of the wheat area is sown with cultivars with this translocationTable 1) the possibility of introeluction of the Sr31 virulentrace Ug99 from Africa is of concern (Antouelli 2000 Germuacutenet aI 2005 1 Ramirez 2005 pers comm) This coulel resultin significant epielemics since elata obtaineel in Kenya eluring2005 inelicateel that the large majority of a group of 72 currentregional cultivars are sqsceptible 01 moelerately susceptible(R Wanyera 2005 pers comm) Given this situation stem rustmay increase in importance in the near future anel it is urgent toincrease testing for resistance to this elisease The introeluction

of resistance genes effective against races virulent on lineswith Sr31 anel Sr24 as well as other effective genes notpresent in the regional germplasm shoulel be emphasiseel(Germaacuten et alo 2005)

The control of wheat rusts continues to be a challengefor breeelers anel rust pathologists in the Southern Cone ofSouth America Breeeling wheat cultivars with effective anelmore elurable resistance is being aelelresseel using traelitionalmethoelologies as well as graelually introelucing newer tools tohelp increase know1eelge about rust resistance anel its efficientuse in breeeling

We appreciate the contribution of Dr Ricardo Madariaga INIA-Chile andDr Robert Mclntosh University of Sydney for reviewing the paper Muchoflhe information from 1999-2004 was obtained eluring the execution ofaproject funded by USDA Funeling ofthe attendance ofthe main author to thecon[erence Global Landscapes in Cereal Rust Control (September 2005)by GRDC is greatly appreciated

Aguayo L (1983) Mejoramiento ele trigos invernales y primaverales enIa zona centro-slU ele Chile In Relmiatildeo ele Melhoristas de Trigo doCone Sul EMBRAPA-CNPT Passo Fundo RS (Coord O de S Rosa)pp 91-100 Diaacutelogo No 9 (Programa Cooperativo dePesquisaAgricolaMontevieleo)

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Antonelli EF (1969) Fuentesde germoplasma ele resistencia a enfermeeladesy plagasln Simposio deI trigo Buenos Aires pp 332-351 (AcademiaNacional de AgronomIacutea y Veterinaria Buenos Aires)

Antonelli EF (1982) Especializacion fisioloacutegica ele Pueeillia reeonditatritiei y p gralllillis tritiei en Ia Argentina en el periacuteodo1978-1981 In Reunioacuten de Especialistas en Royas dei Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBID)

Antonelli EF (1983) Principales patoacutegenos que afectan Ia produccioacuten de trigoen Ia Argentina In Simposio sobre Fitomejoramiento y Produccioacuten eleCereales INTNCIMMYT Marcos Juaacuterez Coacutereloba [sp] (AgenciaEstadounidense para el Desarrollo Internacional Universielad Estatal deOregon)

Antonelli EF (1986) Especializacioacuten fisioloacutegica ele PlIeeillia recollditatritici y P gralllinis tritiei en Ia Argentina en el periacuteodo 1982-1984In Reuniatildeo ele Especialistas em Ferrugens de Cereais de InvernoCNPTErvtBRAPA Passo Funelo RS (Ed CJ Mofestina) pp 37-39Diaacutelogo No 13 (PROCISUR Montevideo)

Antonelli EF (1994) Resistencia en plaacutentula y planta adulta decultivares comerciales argentinos ele trigo y progenitores (antecesores)tradicionales In [nteraccioacuten hospedante-patoacutegeno en hongos biotrofosInforme correspondiente aI afio 1993 [sp] (Instituto ele Geneacutetica EAFavret Castelar)

Antonclli EF (2000) La roya negra dei tallo (PlIceilia gra111illisf sp tritiei)Una ilustre ausente de los campos de trigo (Por cuill1to tiempo mils bull(Grafos Necochea Argentina)

Antonelli EF (2003) La roya anaranjaela (PlIceinia triticillCl Erikss) SobreIa efiacutemera resistencia observada en Ia uacuteltima eleacutecada en cultivarescomerciales ele trigo ele amplia difusioacuten en Ia Argentina (GrafosNecochea Argentina)

Barcellos AL (1982) As ferrugens do trigo no Brasil In Trigo no Brasil(Coorel EA Osoacuterio) pp 377-419 (Flll1dacatildeo Cargill Campinas)

Barcellos AL (1986) Ferrugem da folha do trigo no Brasil Populaccedilatildeopatogecircnica fontes de resistecircncia trigos comerciais perpetuaccedilatildeo econtrole quiacutemico [n Reuniatildeo de Especialistas em Ferrugens de Cereaisde Inverno CNPTEMBRAPA Passo Flmdo RS (Ed CJ Molestina)pp 72-87 Diaacutelogo No 13 (PROC1SUR Montevideo)

Barcellos AL (1991) Dmable leaf rust resistance in wheat in BrazilIn Wheat for the non-traditional warm areas (Ed D Saunders)pp462-465 (C1lIMYT Meacutexico DF)

Barcellos AL (2000) Urgent need for less ephemeral resistance to leaf rustin Brazilian wheat cultivars In 6th International Wheat ConferenceAgricultural Research [nstitute of the 1-LmgarianAcadel11Yof SciencesMartonvaacutesaacuter Hungary

Barcellos AL Aita L (1982) Siacutentese dos resultados das pesquisas sobreferrugem da folha do trigo realizadas no CNPT-EM BRPA Passo FundoRS Brasil de 1980 a 1982 In Reunioacuten de Especialistas en Royasdei Trigo Cono Sur de Ameacuterica INTA Castelar Argentina [sp](Programa IICA-Cono SmBlD)

Barcellos AL Aita L Coehlo ET (1982) Informaccedilotildees preliminares sobrefonte de inoacuteculo de ferrugem da folha e do colmo do trigo em PassoFundo [n Reunioacuten de Especialistas en Royas dcl Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBlD)

Barcellos AL Kohli MM (2003) Resultados da XI XII XlII e XIVcoleccedilatildeo para avaliaccedilatildeo e coleta de ferrugem do colmo e ferrugem dafolha do trigo 1998-2001 EMBRAPA TrigoC[MMYT Documentosno 37 Passo Fundo

Barcellos AL Roelfs AP de Moraes-Fernandes MIB (2000) Inheritance ofadult plant leaf rust resistance in the Brazilian wheat cultivar ToropiPan Disease 84 90-93

l3arcellos AL Tmra C (2004) Search for durable resistance to wheat leafrust in Brazil 1n Abstracts [ofthe] li th International Cereal Rusts andPowdery Mildews Conference Jolm lImes Centre Norwich EnglandUK p A23

Barcellos AL Turra C (2005) Partial resistance - best approach forcontrol of wheat leaf rust in envirolUnents favorable for the diseaseIn Wheat production in stressed envirolUnents abstracts of oral andposter presentations [of the] 7th 1nternational Vheat ConferenceMar dei Pbta Argentina pp 125 (Secretariat of Agriculture AnimalHusbandry Fisheries and Food)

BeckmaJm [(1940) EI problema dei trigo en el Brasil Revisla de a Faculadde AgronollIa (Monevideo) 19 21-36

Betucci L Ferreira V Szpiniak B (1971) Razas fisioloacutegicas ele Pucciniagrallinis Iriliei y Puccinia recondila Iriliei presentes en el Uruguay en1968 Universidael ele Ia Repuacuteblica Boletiacuten N~ 117 Montevideo

van Beuningen LT Kohli MM (1986) Resu1ts from the observalions onthe Latin Al11erican Rust Nursery (ELAR 1981-1983) In Reuniatildeo deEspecialistas em Ferrugens de Cereais de lI1Verno CNPTEMBRAPAPasso Funelo RS (Ed CJ Molestina) pp 7-20 Diaacutelogo No 13(PROC1SUR Montevieleo)

Boasso CS Levine MN (1951) Leaf rust of wheat Puccinia rubigoveraIriliei in Uruguay Phylopalhg) 41 736-741

Boerger A (1934) Consieleraeiones restropectivas acerca de Ia primeraaparieioacuten epieleacutemica ele Ia roya amarilla (Puceinia gullarull (Schm)Erikss et HeJU1)en el Riacuteo ele Ia Plata Revisla del Minislerio de [nduslrlas(Monlevideo) 15-16

Brammer SP Fernaneles MIB Barcellos AL Milach SCK (2004) Geneticanalysis of adult-plant resistanee to leaf rust in a elouble haploid wheat(Triliculll aeslivulll L em Thell) population Genelics and MoecuarBigy 27432-436 eloi I01590S 1415-47572004000300020

Bral11mer SP Worland A Bareellos AL Fernandez MIB (1998) lVlonosomieanalysis of adult-plant resistance to leaf rust in the BraziJian wheatcultivar Toropiacute 1n Proceeelings 9th International Wheat GeneticsSymposium Saskatoon Saskatchewan (Eel AE Slinkarel) v2pp 17-18 (University of Saskatchewan)

Campos PE Loacutepez JR Brach AM (2005) Characterization ofpopulation ofPuccinia Irilieina in Argentina in 2003 anel 2004 In Wheat proeluctionin stresseel envirornllents Abstracts of oral anel posteI presentationsof the 7th International Wheat Conference Mar elel Plata Argentinap I29 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Chaves MS Barcellos AL Germaacuten S Scheeren PL Dei Duca LeleJASilva M Soacute e Caieratildeo E (2005) Population elynamics of PlIccilialriticilain the South Cone region of South America In Wheat proeluction instresseel envirornllents Abstraets of oral anel poster presentations [ofthe] 7th International Wheat Conference Mar elel Plata Argentinap 130 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Coelho ET (1980) Distritribuccedilatildeo prevaJencia de novas razas fisiologicasde PlIccilia gmlllinis tritici (ferrugem do colmo elo trigo) no Brasil ele1974 a 1978 [n Xl Reuniatildeo Nacional de Pcsquisa ele Trigo PortoAlegre RS Brasil v 2 pp 9-22 (EMBRAPA Centro Nacional elePesquisa ele Trigo Passo Funelo)

Coelho E (1982) Siacutentese elos resultaelos elas pesquisas sobre ferrugem docolmo do trigo realizaelas no Centro Nacional ele Pesquisa ele Trigo(CNPT) EMBRAPA Passo FIUlelORS Brasil 1980 e 1981 In Reunioacutenele Especialistas en Royas elel Trigo Cono Sur ele Ameacuterica INTACastelar Argentina [sp] (Programa IlCA-Cono SurBlD)

Coelho E (1986) Siacutentese elos estuelos com ferrugem elo colmo elo trigo-1982 a 1984 In Reuniatildeo de Especialistas em Ferrugens ele Cereaisele Inverno CNPTIEMBRAPA Passo Funelo RS (Eel CJ Molestina)pp 107-110 Diaacutelogo No 13 (PROCISUR Montevieleo)

Dyck PL (1989) The inheritance of leaf rust resistance in wheat cultivarsKenyon anel B Manantial Caladial JOllma of Pall Seielce 691113-1117

Dyck PL (199 j) Genetics of aelult plant leaf rust resistance in ChineseSpring and Sturely wheats Crop Scielce 24 309-311

Dyck PL Kerber ER (1977) lnheritance of leaf rust resistance in wheatcultivars Rafaela anel EAP 26127 anel chromosome location of Irl7Caladial JOllma ofGelelics ald Cytgy 19 355-358

Dyck PL Samborski DL (1968a) Genetics of resistance to leaf rust in theconunon wheat varieties Webster Loros Brevit Carina Malakoff anelCentenario Caladial JOllma ofGelelics ald Cytgy 107-17

Dyck PL Samborski DL (1968b) Host-parasite interactions involvingtwo genes for leaf rust resistance in wheat ln Proceeelings of theThirel IJlternational Wheat Genetics Symposium Canberra Australia(Eels KW Finlay KW Shepherd) pp 245-250 (Australian Acaelemy ofScience Canberra)

Dyck PL Samborski DL (1970) The genetics of two alleles for leaf rustresistance at the [r14 locus in wheat Caladial JOllma of Gelelicsald C)lgy 12 689-694

Dyck PL Samborski DL (1982) The inheritance of resistance to Puceiliarecoldila in a group of conU110n wheat cultivars Caladial JOllma ofGelelics ald CylOogy 24273-283

Dyck PL Samborski DL Anelerson RG (1966) lnheritance of adultplant-Ieaf rust resistance eleriveel from the conmlon wleat varietiesExchange anel Frontana Caladial JOtlma oGelelics ald Cygy 8665-671

rlOSTAT (2006) Core production data (online) (FAO Rome) Availableat httpfaostatfaoorglsite340elefaultaspx Verifieel July 2006

Germaacuten S Caffarel JC (1999) Roya estriaela ele trigo In Jornaela de Cultivosele Invierno INIA La Estanzuela Colonia Uruguay pp 25-32 SerieActivielaeles ele Difusioacuten No 188 La Estanzuela

Germaacuten S Diaz M Verges R Castro M (2005) Breeeling for resistance towheat rusts in a highly favourable envirolUllent for eliseases In Wheatproeluction in stresseel envir Imlents Abstracts of oral anel posterpresentations [of theJ 7th International Wheat Conference Marelel Plata Argentina pp 139 (Secretariat of Agriculture AnimalHusbanelry fisheries anel Fooel)

epielemics in most of the region (from Chile to Rio Graneleelo Sul in Brazil) causing extremely high losses in theeastern epielemio10gical zone (Boerger 1934 Vallega 1938)The presence in Argentina anel Uruguay of COl11l11onracesfounel in Chile (Straib 1937) inelicates stripe rust probablymigrateel through the Aneles liom Chile to the easteru part ofthe continent

Yr18 anel tightly linkeel Lr34 (McIntosh 1992 Singh1992) were probably present in tolerant wheat lines selecteeluneler the extreme 1929 anel 1930 stripe rust epielel11ics assuggesteel by Dyck (1991) anel Kolmer (1996) The Brazil iancultivar Fronteira one of Frontanas parents selecteel at BageacuteExperimental Station anel releaseel in 1934 was highly resistantto stripe rust (Beckmann 1940) ln Argentina cv Chino alsoknown as Chinese 166 expresseel the most effective resistanceanel was useel in crosses from which aelapteel resistant lines wereeleriveel (Val1ega 1938)

Unlike other regions of the worlel where the importanceof stripe rust is increasing no other wielespreael epielemichas occurreel in the eastern epielemiological zone anel theelisease is currently not economically important ln the southernwheat arca of Argentina only sporaelic localiseel outbreakshave been observeel on highly susceptible cultivars Similarloca1iseel epielemics have also been observeel in southern Brazilaifecting cv Curitiba eluring 1968 (Schraml11 1969) anel cvTifton eluring 1980 ln 1998 a moelerate epielemic ofstripe rustoccurreel in Uruguay (Germaacuten anel Caifare1 1999) During thisepielemic some cultivars with the lBLIRS translocation suchas Estanzuela Carelenal (Veery 3) were susceptible inelicatingthe presence ofvirulence on Yr9 Many cultivars known to carryYr18Lr34 hael 10w to intermeeliate stripe rust severities

Puccinia slriiformis probab1y oversummers in the valleys ofthe Argentinean Aneles (Neuqueacuten anel Rio Negro provinces)on wheat anel wilel Hordeum spp (Vallega anel Favret 1947)elelaying the elispersal ofinoculum to the major proeluction areasin the north Most germp1asl11 from Argentina Brazil Paraguayanel Urllguay is moelerately susceptible or susceptible uneler theheavy elisease conelitions present in Chile The absence ofearlyinfections even in the presence ofsusceptible cllltivars inelicatesthat inoculum is usually not present at early stages of cropelevelopment anel that oversummering does not regularly OCCllrin the l11ain wheat areas Uneler these conelitions avoieling theuse of highly susceptible cultivars anel maintaining resistancelevels such as those conferreel by Yr18 or other genes withsimilar eiacuteTect appears to be an effective strategy to prcvcntstripe rust epielemics in Uruguay (Germaacuten anel Caffarel 1999)anel the rest of the eastem epielemiologic zanc ln aelelitionthe increaseel use of durable APR to leaf rust often associatedwith APR to stripe rust (Singh 1992 Singh anel Rajaram 1994Singh el ai 2003) will also increase the leveI of resistance tostripe rust

Wheat stem rustOistribution and occurrenceAlthough the incielence of steni rust historically has been moresporaelic than that ofleafrust it causeel higher 1evels of elamageeluring severe epielemics It was consielereelthe most elestructivewheat rust in Brazil (ela Silva 1966) Paraguay (ele Vieelma anel

Bozzano 1986) Uruguay (Ribeiro 1952) the northem wheatgrowing area ofChile (Hacke 1990) anel the northern anel central-north wheat area of Argentina (Val1ega anel Favret 1952)

Oversummering of stem rust has been observeel on volunteerwheat anel barley plants in Uruguay anel in the south of BuenosAires province (Argentina) where it is frequently present in lhesummer nursery at Balcarce (1 Nisi 2005 pers comm) Stemrust also oversuml11ers locally in Brazil (Barcellos et ai 1982)

A very severe stem rust epielemic occurreel in Argentinaanel other Southern Cone countries in 1950 (Antonelli2000) The majority of commercia1 cultivars from regionalbreeeling programs were susceptible to the pathogen populationelominateel by a variant of race 15 (effective genesSr67a222425262731 ineffective genes Sr8a8bge9a9g1011 13173037 elenominateel 15 (63) by Antonel1i 1969)In 1974 a new race (effective genes Sr8a8bge11 2224252627313 7 ineffective genes Sr67a9a9gl 0131730elenominateel II MeR in Argentina anel Gil in Brazil)viru1ent on most of the popular Argentinean (Antonelli 2000)Brazilian (Coelho 1980) anel Uruguayan cultivars (Luizzi et aI1980) causeel wielespreael epielemics uneler unusually favourableenvironmenta1 conelitions eluring 1975-1976

Wheat stem rust has not been severely epielemic for over 2elecaeles This was coincielent with the increaseel anel wielespreaeluse ofcultivars with lBL1RS (Sr31) (Antonelli 2000) During1975-2003 2 stem rust epielemics (1976 anel 1981) wereobserveel inPasso funelo RS Brazil (C ele Souza 2005 perscomm) Localised epielemir outbreaks occurred during the1990s on some wielely grown cultivars in Paraguay (ltapuacutea35) Brazil (CEP 14) anel Argentina (Victoria lNTA) Since2000 stem rust has been observeel sporaelically on highlysusceptible materiaIs in experimental fields throughout lheregion The release of stem rust susceptible cultivars suchas Klein Escorpioacuten Buck Yatasto anel the French cultivarBaguette 10 led to the reappearance ofthe clisease in c0111mercialfielels in northern Argentina in 2001 anel 2003 (1 Nisi 2005 perscomm)

The pathogen populationDuring 1949-199430 elifferentP graminis races were elescribeelin Brazil These combineel virulence on 4 to 14 SI genes (Sr5Sr6 Sr7a Sr8 Sr9a Sr9b Srge SI10 SI11 Sr12 SI13 Sr14Sr17 Sr29 Sr30 SI36 Sr37) Most olel races ielentifieel inArgentina anel Brazil were lost from the collections elue toreeluction in research on stem rust Few races have been founelsince 2000 One race (RTT-TR Brazilian elesignation 030)has been prevalent for many years in Brazil anel UruguaySince 2002 some changes in the pathogen population havebeen eletecteel in Brazil (A Barcellos C ele Souza S GermaacutenC Turra anel M Segalin 2003 unpublisheel elata) Argentinaanel Uruguay Genes Sr22 Sr24 Sr25 Sr26 Sr31 Sr32 Sr33Sr35 Sr39 anel Sr40 are currently effective across the regionSr27hael intermeeliate stem rust severity levels in Chile in 1984(Hacke 1986) Sr38 has not been testeel although CIMMYT lineMilan that may carry this gene has hael high fielel severity withsusceptible reaction to stem rust in Uruguay anel Paraguay ln2005 a very severe stem rust epidemic on international nurseriesfTom CIMMYT anel the Southern Cone region was observeel inSanta Cruz Bolivia

Breeding for resistance

Stem rust resistance was one of the major wheat breeelingobjectives when the elisease was important acrass the regionln some countries stem rust resistance was a requirement forcultivar release Sources of stem rust resistance were selecteelfrom the same international nurseries useel to select for leaf rustresistance During the 1950s anel 1960s sources of resistanceielentifieel in Argentina were Kenya 58 Kenya 117A EgyptNA 10 1 some lines from Egypt N95 Kenya Governor KenyaStanelarel (VaI lega 1940) Mayo 54 Kentana 51A Yaqui 53 anelnew resistance ielentifieel fram the lSWRN (Antonelli 2000)ln Brazil the best sources of resistance provieleel to breeelingprograms were Reel Egyptian Kenya 58 anel Kenya FarmerCultivars with resistance fram these sources became wielespreael(ela Silva 1966)

Sr22 Sr24 Sr25 Sr26 S27 Sr31 Sr32 Sr33 (Coelho 19821986) anel Sr2 (C Sousa pers comm) have been useel inEMBRAPA-CNPT ln the Brazilian company OR sources withslow rusting type of resistance are being useel

Presently the most important genes conferring resistance inthe regional germplasm are Sr31 anel Sr24 The presence of S31is inelicateel by the presence ofthe 1BLl RS translocation anelorthe presence of Lr26 The presence of Lr24 inelicates the presenceof Sr24 The introeluction anel use ofSr31 anel Sr24 in the regionalgermplasm were as elescribeel for the 1inkeel leaf rust resistancegenes Although it is not known if S24 anel Sr31 are presentsingly 01 in combination with other resistance genes the basisof resistance in the regional germplasm appears to be narrowGenes Sr5 S6 S7a Sr8a Sr8b Sr9b Sr 10 S111 anel Sr30 areprobably present (but largely ineifective) in some Argentineancultivars (Antonelli 2000) APR genes such as S2 are presentin many Brazilian lines anel cultivars (C ele Souza 2005 persCOIllI11)

The absence ofthe elisease anel reeluceel pathogen variabilityhas elecreaseel the opportunities of selection for resistanceanel also the priority that breeeling programs have assigneel tothis characteristic As a result some susceptible cultivars havebeen recently releaseel inclueling some of European origino ltwas estimateel that gt20 of the regional vheat area in 2004was sown to cultivars known to be susceptib1e to stem rust(Table 1) anel this area continues to increase The increasingarea of susceptible cultivars 1ll)Y result not on1y in inoculumbuilel-up anel higher infections on these cultivars but also toan increaseel likelihooel of eleveloping new virulent races oncurrently resistant cultivars ln aelelition the introeluction ofraces with S24 virulence from South Africa 01 lnelia coulelcause significant losses Because the 1BL1 RS translocation ispresent in a high praportion of the regional germplasm (gt 50of the wheat area is sown with cultivars with this translocationTable 1) the possibility of introeluction of the Sr31 virulentrace Ug99 from Africa is of concern (Antouelli 2000 Germuacutenet aI 2005 1 Ramirez 2005 pers comm) This coulel resultin significant epielemics since elata obtaineel in Kenya eluring2005 inelicateel that the large majority of a group of 72 currentregional cultivars are sqsceptible 01 moelerately susceptible(R Wanyera 2005 pers comm) Given this situation stem rustmay increase in importance in the near future anel it is urgent toincrease testing for resistance to this elisease The introeluction

of resistance genes effective against races virulent on lineswith Sr31 anel Sr24 as well as other effective genes notpresent in the regional germplasm shoulel be emphasiseel(Germaacuten et alo 2005)

The control of wheat rusts continues to be a challengefor breeelers anel rust pathologists in the Southern Cone ofSouth America Breeeling wheat cultivars with effective anelmore elurable resistance is being aelelresseel using traelitionalmethoelologies as well as graelually introelucing newer tools tohelp increase know1eelge about rust resistance anel its efficientuse in breeeling

We appreciate the contribution of Dr Ricardo Madariaga INIA-Chile andDr Robert Mclntosh University of Sydney for reviewing the paper Muchoflhe information from 1999-2004 was obtained eluring the execution ofaproject funded by USDA Funeling ofthe attendance ofthe main author to thecon[erence Global Landscapes in Cereal Rust Control (September 2005)by GRDC is greatly appreciated

Aguayo L (1983) Mejoramiento ele trigos invernales y primaverales enIa zona centro-slU ele Chile In Relmiatildeo ele Melhoristas de Trigo doCone Sul EMBRAPA-CNPT Passo Fundo RS (Coord O de S Rosa)pp 91-100 Diaacutelogo No 9 (Programa Cooperativo dePesquisaAgricolaMontevieleo)

Anelrade Vilaro O (J 990) Polvillo estriado o roya amarilla (Puecilliastriiforlllis Westenel) deI trigo en Ia zona sur de Chile Institutoele Investigaciones Agropecuarias Estacioacuten Experimental CarillancaBoletiacuten Teacutecnico No 164 Temuco

Antonelli EF (1969) Fuentesde germoplasma ele resistencia a enfermeeladesy plagasln Simposio deI trigo Buenos Aires pp 332-351 (AcademiaNacional de AgronomIacutea y Veterinaria Buenos Aires)

Antonelli EF (1982) Especializacion fisioloacutegica ele Pueeillia reeonditatritiei y p gralllillis tritiei en Ia Argentina en el periacuteodo1978-1981 In Reunioacuten de Especialistas en Royas dei Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBID)

Antonelli EF (1983) Principales patoacutegenos que afectan Ia produccioacuten de trigoen Ia Argentina In Simposio sobre Fitomejoramiento y Produccioacuten eleCereales INTNCIMMYT Marcos Juaacuterez Coacutereloba [sp] (AgenciaEstadounidense para el Desarrollo Internacional Universielad Estatal deOregon)

Antonelli EF (1986) Especializacioacuten fisioloacutegica ele PlIeeillia recollditatritici y P gralllinis tritiei en Ia Argentina en el periacuteodo 1982-1984In Reuniatildeo ele Especialistas em Ferrugens de Cereais de InvernoCNPTErvtBRAPA Passo Funelo RS (Ed CJ Mofestina) pp 37-39Diaacutelogo No 13 (PROCISUR Montevideo)

Antonelli EF (1994) Resistencia en plaacutentula y planta adulta decultivares comerciales argentinos ele trigo y progenitores (antecesores)tradicionales In [nteraccioacuten hospedante-patoacutegeno en hongos biotrofosInforme correspondiente aI afio 1993 [sp] (Instituto ele Geneacutetica EAFavret Castelar)

Antonclli EF (2000) La roya negra dei tallo (PlIceilia gra111illisf sp tritiei)Una ilustre ausente de los campos de trigo (Por cuill1to tiempo mils bull(Grafos Necochea Argentina)

Antonelli EF (2003) La roya anaranjaela (PlIceinia triticillCl Erikss) SobreIa efiacutemera resistencia observada en Ia uacuteltima eleacutecada en cultivarescomerciales ele trigo ele amplia difusioacuten en Ia Argentina (GrafosNecochea Argentina)

Barcellos AL (1982) As ferrugens do trigo no Brasil In Trigo no Brasil(Coorel EA Osoacuterio) pp 377-419 (Flll1dacatildeo Cargill Campinas)

Barcellos AL (1986) Ferrugem da folha do trigo no Brasil Populaccedilatildeopatogecircnica fontes de resistecircncia trigos comerciais perpetuaccedilatildeo econtrole quiacutemico [n Reuniatildeo de Especialistas em Ferrugens de Cereaisde Inverno CNPTEMBRAPA Passo Flmdo RS (Ed CJ Molestina)pp 72-87 Diaacutelogo No 13 (PROC1SUR Montevideo)

Barcellos AL (1991) Dmable leaf rust resistance in wheat in BrazilIn Wheat for the non-traditional warm areas (Ed D Saunders)pp462-465 (C1lIMYT Meacutexico DF)

Barcellos AL (2000) Urgent need for less ephemeral resistance to leaf rustin Brazilian wheat cultivars In 6th International Wheat ConferenceAgricultural Research [nstitute of the 1-LmgarianAcadel11Yof SciencesMartonvaacutesaacuter Hungary

Barcellos AL Aita L (1982) Siacutentese dos resultados das pesquisas sobreferrugem da folha do trigo realizadas no CNPT-EM BRPA Passo FundoRS Brasil de 1980 a 1982 In Reunioacuten de Especialistas en Royasdei Trigo Cono Sur de Ameacuterica INTA Castelar Argentina [sp](Programa IICA-Cono SmBlD)

Barcellos AL Aita L Coehlo ET (1982) Informaccedilotildees preliminares sobrefonte de inoacuteculo de ferrugem da folha e do colmo do trigo em PassoFundo [n Reunioacuten de Especialistas en Royas dcl Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBlD)

Barcellos AL Kohli MM (2003) Resultados da XI XII XlII e XIVcoleccedilatildeo para avaliaccedilatildeo e coleta de ferrugem do colmo e ferrugem dafolha do trigo 1998-2001 EMBRAPA TrigoC[MMYT Documentosno 37 Passo Fundo

Barcellos AL Roelfs AP de Moraes-Fernandes MIB (2000) Inheritance ofadult plant leaf rust resistance in the Brazilian wheat cultivar ToropiPan Disease 84 90-93

l3arcellos AL Tmra C (2004) Search for durable resistance to wheat leafrust in Brazil 1n Abstracts [ofthe] li th International Cereal Rusts andPowdery Mildews Conference Jolm lImes Centre Norwich EnglandUK p A23

Barcellos AL Turra C (2005) Partial resistance - best approach forcontrol of wheat leaf rust in envirolUnents favorable for the diseaseIn Wheat production in stressed envirolUnents abstracts of oral andposter presentations [of the] 7th 1nternational Vheat ConferenceMar dei Pbta Argentina pp 125 (Secretariat of Agriculture AnimalHusbandry Fisheries and Food)

BeckmaJm [(1940) EI problema dei trigo en el Brasil Revisla de a Faculadde AgronollIa (Monevideo) 19 21-36

Betucci L Ferreira V Szpiniak B (1971) Razas fisioloacutegicas ele Pucciniagrallinis Iriliei y Puccinia recondila Iriliei presentes en el Uruguay en1968 Universidael ele Ia Repuacuteblica Boletiacuten N~ 117 Montevideo

van Beuningen LT Kohli MM (1986) Resu1ts from the observalions onthe Latin Al11erican Rust Nursery (ELAR 1981-1983) In Reuniatildeo deEspecialistas em Ferrugens de Cereais de lI1Verno CNPTEMBRAPAPasso Funelo RS (Ed CJ Molestina) pp 7-20 Diaacutelogo No 13(PROC1SUR Montevieleo)

Boasso CS Levine MN (1951) Leaf rust of wheat Puccinia rubigoveraIriliei in Uruguay Phylopalhg) 41 736-741

Boerger A (1934) Consieleraeiones restropectivas acerca de Ia primeraaparieioacuten epieleacutemica ele Ia roya amarilla (Puceinia gullarull (Schm)Erikss et HeJU1)en el Riacuteo ele Ia Plata Revisla del Minislerio de [nduslrlas(Monlevideo) 15-16

Brammer SP Fernaneles MIB Barcellos AL Milach SCK (2004) Geneticanalysis of adult-plant resistanee to leaf rust in a elouble haploid wheat(Triliculll aeslivulll L em Thell) population Genelics and MoecuarBigy 27432-436 eloi I01590S 1415-47572004000300020

Bral11mer SP Worland A Bareellos AL Fernandez MIB (1998) lVlonosomieanalysis of adult-plant resistance to leaf rust in the BraziJian wheatcultivar Toropiacute 1n Proceeelings 9th International Wheat GeneticsSymposium Saskatoon Saskatchewan (Eel AE Slinkarel) v2pp 17-18 (University of Saskatchewan)

Campos PE Loacutepez JR Brach AM (2005) Characterization ofpopulation ofPuccinia Irilieina in Argentina in 2003 anel 2004 In Wheat proeluctionin stresseel envirornllents Abstracts of oral anel posteI presentationsof the 7th International Wheat Conference Mar elel Plata Argentinap I29 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Chaves MS Barcellos AL Germaacuten S Scheeren PL Dei Duca LeleJASilva M Soacute e Caieratildeo E (2005) Population elynamics of PlIccilialriticilain the South Cone region of South America In Wheat proeluction instresseel envirornllents Abstraets of oral anel poster presentations [ofthe] 7th International Wheat Conference Mar elel Plata Argentinap 130 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Coelho ET (1980) Distritribuccedilatildeo prevaJencia de novas razas fisiologicasde PlIccilia gmlllinis tritici (ferrugem do colmo elo trigo) no Brasil ele1974 a 1978 [n Xl Reuniatildeo Nacional de Pcsquisa ele Trigo PortoAlegre RS Brasil v 2 pp 9-22 (EMBRAPA Centro Nacional elePesquisa ele Trigo Passo Funelo)

Coelho E (1982) Siacutentese elos resultaelos elas pesquisas sobre ferrugem docolmo do trigo realizaelas no Centro Nacional ele Pesquisa ele Trigo(CNPT) EMBRAPA Passo FIUlelORS Brasil 1980 e 1981 In Reunioacutenele Especialistas en Royas elel Trigo Cono Sur ele Ameacuterica INTACastelar Argentina [sp] (Programa IlCA-Cono SurBlD)

Coelho E (1986) Siacutentese elos estuelos com ferrugem elo colmo elo trigo-1982 a 1984 In Reuniatildeo de Especialistas em Ferrugens ele Cereaisele Inverno CNPTIEMBRAPA Passo Funelo RS (Eel CJ Molestina)pp 107-110 Diaacutelogo No 13 (PROCISUR Montevieleo)

Dyck PL (1989) The inheritance of leaf rust resistance in wheat cultivarsKenyon anel B Manantial Caladial JOllma of Pall Seielce 691113-1117

Dyck PL (199 j) Genetics of aelult plant leaf rust resistance in ChineseSpring and Sturely wheats Crop Scielce 24 309-311

Dyck PL Kerber ER (1977) lnheritance of leaf rust resistance in wheatcultivars Rafaela anel EAP 26127 anel chromosome location of Irl7Caladial JOllma ofGelelics ald Cytgy 19 355-358

Dyck PL Samborski DL (1968a) Genetics of resistance to leaf rust in theconunon wheat varieties Webster Loros Brevit Carina Malakoff anelCentenario Caladial JOllma ofGelelics ald Cytgy 107-17

Dyck PL Samborski DL (1968b) Host-parasite interactions involvingtwo genes for leaf rust resistance in wheat ln Proceeelings of theThirel IJlternational Wheat Genetics Symposium Canberra Australia(Eels KW Finlay KW Shepherd) pp 245-250 (Australian Acaelemy ofScience Canberra)

Dyck PL Samborski DL (1970) The genetics of two alleles for leaf rustresistance at the [r14 locus in wheat Caladial JOllma of Gelelicsald C)lgy 12 689-694

Dyck PL Samborski DL (1982) The inheritance of resistance to Puceiliarecoldila in a group of conU110n wheat cultivars Caladial JOllma ofGelelics ald CylOogy 24273-283

Dyck PL Samborski DL Anelerson RG (1966) lnheritance of adultplant-Ieaf rust resistance eleriveel from the conmlon wleat varietiesExchange anel Frontana Caladial JOtlma oGelelics ald Cygy 8665-671

rlOSTAT (2006) Core production data (online) (FAO Rome) Availableat httpfaostatfaoorglsite340elefaultaspx Verifieel July 2006

Germaacuten S Caffarel JC (1999) Roya estriaela ele trigo In Jornaela de Cultivosele Invierno INIA La Estanzuela Colonia Uruguay pp 25-32 SerieActivielaeles ele Difusioacuten No 188 La Estanzuela

Germaacuten S Diaz M Verges R Castro M (2005) Breeeling for resistance towheat rusts in a highly favourable envirolUllent for eliseases In Wheatproeluction in stresseel envir Imlents Abstracts of oral anel posterpresentations [of theJ 7th International Wheat Conference Marelel Plata Argentina pp 139 (Secretariat of Agriculture AnimalHusbanelry fisheries anel Fooel)

Breeding for resistance

Stem rust resistance was one of the major wheat breeelingobjectives when the elisease was important acrass the regionln some countries stem rust resistance was a requirement forcultivar release Sources of stem rust resistance were selecteelfrom the same international nurseries useel to select for leaf rustresistance During the 1950s anel 1960s sources of resistanceielentifieel in Argentina were Kenya 58 Kenya 117A EgyptNA 10 1 some lines from Egypt N95 Kenya Governor KenyaStanelarel (VaI lega 1940) Mayo 54 Kentana 51A Yaqui 53 anelnew resistance ielentifieel fram the lSWRN (Antonelli 2000)ln Brazil the best sources of resistance provieleel to breeelingprograms were Reel Egyptian Kenya 58 anel Kenya FarmerCultivars with resistance fram these sources became wielespreael(ela Silva 1966)

Sr22 Sr24 Sr25 Sr26 S27 Sr31 Sr32 Sr33 (Coelho 19821986) anel Sr2 (C Sousa pers comm) have been useel inEMBRAPA-CNPT ln the Brazilian company OR sources withslow rusting type of resistance are being useel

Presently the most important genes conferring resistance inthe regional germplasm are Sr31 anel Sr24 The presence of S31is inelicateel by the presence ofthe 1BLl RS translocation anelorthe presence of Lr26 The presence of Lr24 inelicates the presenceof Sr24 The introeluction anel use ofSr31 anel Sr24 in the regionalgermplasm were as elescribeel for the 1inkeel leaf rust resistancegenes Although it is not known if S24 anel Sr31 are presentsingly 01 in combination with other resistance genes the basisof resistance in the regional germplasm appears to be narrowGenes Sr5 S6 S7a Sr8a Sr8b Sr9b Sr 10 S111 anel Sr30 areprobably present (but largely ineifective) in some Argentineancultivars (Antonelli 2000) APR genes such as S2 are presentin many Brazilian lines anel cultivars (C ele Souza 2005 persCOIllI11)

The absence ofthe elisease anel reeluceel pathogen variabilityhas elecreaseel the opportunities of selection for resistanceanel also the priority that breeeling programs have assigneel tothis characteristic As a result some susceptible cultivars havebeen recently releaseel inclueling some of European origino ltwas estimateel that gt20 of the regional vheat area in 2004was sown to cultivars known to be susceptib1e to stem rust(Table 1) anel this area continues to increase The increasingarea of susceptible cultivars 1ll)Y result not on1y in inoculumbuilel-up anel higher infections on these cultivars but also toan increaseel likelihooel of eleveloping new virulent races oncurrently resistant cultivars ln aelelition the introeluction ofraces with S24 virulence from South Africa 01 lnelia coulelcause significant losses Because the 1BL1 RS translocation ispresent in a high praportion of the regional germplasm (gt 50of the wheat area is sown with cultivars with this translocationTable 1) the possibility of introeluction of the Sr31 virulentrace Ug99 from Africa is of concern (Antouelli 2000 Germuacutenet aI 2005 1 Ramirez 2005 pers comm) This coulel resultin significant epielemics since elata obtaineel in Kenya eluring2005 inelicateel that the large majority of a group of 72 currentregional cultivars are sqsceptible 01 moelerately susceptible(R Wanyera 2005 pers comm) Given this situation stem rustmay increase in importance in the near future anel it is urgent toincrease testing for resistance to this elisease The introeluction

of resistance genes effective against races virulent on lineswith Sr31 anel Sr24 as well as other effective genes notpresent in the regional germplasm shoulel be emphasiseel(Germaacuten et alo 2005)

The control of wheat rusts continues to be a challengefor breeelers anel rust pathologists in the Southern Cone ofSouth America Breeeling wheat cultivars with effective anelmore elurable resistance is being aelelresseel using traelitionalmethoelologies as well as graelually introelucing newer tools tohelp increase know1eelge about rust resistance anel its efficientuse in breeeling

We appreciate the contribution of Dr Ricardo Madariaga INIA-Chile andDr Robert Mclntosh University of Sydney for reviewing the paper Muchoflhe information from 1999-2004 was obtained eluring the execution ofaproject funded by USDA Funeling ofthe attendance ofthe main author to thecon[erence Global Landscapes in Cereal Rust Control (September 2005)by GRDC is greatly appreciated

Aguayo L (1983) Mejoramiento ele trigos invernales y primaverales enIa zona centro-slU ele Chile In Relmiatildeo ele Melhoristas de Trigo doCone Sul EMBRAPA-CNPT Passo Fundo RS (Coord O de S Rosa)pp 91-100 Diaacutelogo No 9 (Programa Cooperativo dePesquisaAgricolaMontevieleo)

Anelrade Vilaro O (J 990) Polvillo estriado o roya amarilla (Puecilliastriiforlllis Westenel) deI trigo en Ia zona sur de Chile Institutoele Investigaciones Agropecuarias Estacioacuten Experimental CarillancaBoletiacuten Teacutecnico No 164 Temuco

Antonelli EF (1969) Fuentesde germoplasma ele resistencia a enfermeeladesy plagasln Simposio deI trigo Buenos Aires pp 332-351 (AcademiaNacional de AgronomIacutea y Veterinaria Buenos Aires)

Antonelli EF (1982) Especializacion fisioloacutegica ele Pueeillia reeonditatritiei y p gralllillis tritiei en Ia Argentina en el periacuteodo1978-1981 In Reunioacuten de Especialistas en Royas dei Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBID)

Antonelli EF (1983) Principales patoacutegenos que afectan Ia produccioacuten de trigoen Ia Argentina In Simposio sobre Fitomejoramiento y Produccioacuten eleCereales INTNCIMMYT Marcos Juaacuterez Coacutereloba [sp] (AgenciaEstadounidense para el Desarrollo Internacional Universielad Estatal deOregon)

Antonelli EF (1986) Especializacioacuten fisioloacutegica ele PlIeeillia recollditatritici y P gralllinis tritiei en Ia Argentina en el periacuteodo 1982-1984In Reuniatildeo ele Especialistas em Ferrugens de Cereais de InvernoCNPTErvtBRAPA Passo Funelo RS (Ed CJ Mofestina) pp 37-39Diaacutelogo No 13 (PROCISUR Montevideo)

Antonelli EF (1994) Resistencia en plaacutentula y planta adulta decultivares comerciales argentinos ele trigo y progenitores (antecesores)tradicionales In [nteraccioacuten hospedante-patoacutegeno en hongos biotrofosInforme correspondiente aI afio 1993 [sp] (Instituto ele Geneacutetica EAFavret Castelar)

Antonclli EF (2000) La roya negra dei tallo (PlIceilia gra111illisf sp tritiei)Una ilustre ausente de los campos de trigo (Por cuill1to tiempo mils bull(Grafos Necochea Argentina)

Antonelli EF (2003) La roya anaranjaela (PlIceinia triticillCl Erikss) SobreIa efiacutemera resistencia observada en Ia uacuteltima eleacutecada en cultivarescomerciales ele trigo ele amplia difusioacuten en Ia Argentina (GrafosNecochea Argentina)

Barcellos AL (1982) As ferrugens do trigo no Brasil In Trigo no Brasil(Coorel EA Osoacuterio) pp 377-419 (Flll1dacatildeo Cargill Campinas)

Barcellos AL (1986) Ferrugem da folha do trigo no Brasil Populaccedilatildeopatogecircnica fontes de resistecircncia trigos comerciais perpetuaccedilatildeo econtrole quiacutemico [n Reuniatildeo de Especialistas em Ferrugens de Cereaisde Inverno CNPTEMBRAPA Passo Flmdo RS (Ed CJ Molestina)pp 72-87 Diaacutelogo No 13 (PROC1SUR Montevideo)

Barcellos AL (1991) Dmable leaf rust resistance in wheat in BrazilIn Wheat for the non-traditional warm areas (Ed D Saunders)pp462-465 (C1lIMYT Meacutexico DF)

Barcellos AL (2000) Urgent need for less ephemeral resistance to leaf rustin Brazilian wheat cultivars In 6th International Wheat ConferenceAgricultural Research [nstitute of the 1-LmgarianAcadel11Yof SciencesMartonvaacutesaacuter Hungary

Barcellos AL Aita L (1982) Siacutentese dos resultados das pesquisas sobreferrugem da folha do trigo realizadas no CNPT-EM BRPA Passo FundoRS Brasil de 1980 a 1982 In Reunioacuten de Especialistas en Royasdei Trigo Cono Sur de Ameacuterica INTA Castelar Argentina [sp](Programa IICA-Cono SmBlD)

Barcellos AL Aita L Coehlo ET (1982) Informaccedilotildees preliminares sobrefonte de inoacuteculo de ferrugem da folha e do colmo do trigo em PassoFundo [n Reunioacuten de Especialistas en Royas dcl Trigo Cono Surde Ameacuterica INTA Castelar Argentina [sp] (Programa JlCA-ConoSurBlD)

Barcellos AL Kohli MM (2003) Resultados da XI XII XlII e XIVcoleccedilatildeo para avaliaccedilatildeo e coleta de ferrugem do colmo e ferrugem dafolha do trigo 1998-2001 EMBRAPA TrigoC[MMYT Documentosno 37 Passo Fundo

Barcellos AL Roelfs AP de Moraes-Fernandes MIB (2000) Inheritance ofadult plant leaf rust resistance in the Brazilian wheat cultivar ToropiPan Disease 84 90-93

l3arcellos AL Tmra C (2004) Search for durable resistance to wheat leafrust in Brazil 1n Abstracts [ofthe] li th International Cereal Rusts andPowdery Mildews Conference Jolm lImes Centre Norwich EnglandUK p A23

Barcellos AL Turra C (2005) Partial resistance - best approach forcontrol of wheat leaf rust in envirolUnents favorable for the diseaseIn Wheat production in stressed envirolUnents abstracts of oral andposter presentations [of the] 7th 1nternational Vheat ConferenceMar dei Pbta Argentina pp 125 (Secretariat of Agriculture AnimalHusbandry Fisheries and Food)

BeckmaJm [(1940) EI problema dei trigo en el Brasil Revisla de a Faculadde AgronollIa (Monevideo) 19 21-36

Betucci L Ferreira V Szpiniak B (1971) Razas fisioloacutegicas ele Pucciniagrallinis Iriliei y Puccinia recondila Iriliei presentes en el Uruguay en1968 Universidael ele Ia Repuacuteblica Boletiacuten N~ 117 Montevideo

van Beuningen LT Kohli MM (1986) Resu1ts from the observalions onthe Latin Al11erican Rust Nursery (ELAR 1981-1983) In Reuniatildeo deEspecialistas em Ferrugens de Cereais de lI1Verno CNPTEMBRAPAPasso Funelo RS (Ed CJ Molestina) pp 7-20 Diaacutelogo No 13(PROC1SUR Montevieleo)

Boasso CS Levine MN (1951) Leaf rust of wheat Puccinia rubigoveraIriliei in Uruguay Phylopalhg) 41 736-741

Boerger A (1934) Consieleraeiones restropectivas acerca de Ia primeraaparieioacuten epieleacutemica ele Ia roya amarilla (Puceinia gullarull (Schm)Erikss et HeJU1)en el Riacuteo ele Ia Plata Revisla del Minislerio de [nduslrlas(Monlevideo) 15-16

Brammer SP Fernaneles MIB Barcellos AL Milach SCK (2004) Geneticanalysis of adult-plant resistanee to leaf rust in a elouble haploid wheat(Triliculll aeslivulll L em Thell) population Genelics and MoecuarBigy 27432-436 eloi I01590S 1415-47572004000300020

Bral11mer SP Worland A Bareellos AL Fernandez MIB (1998) lVlonosomieanalysis of adult-plant resistance to leaf rust in the BraziJian wheatcultivar Toropiacute 1n Proceeelings 9th International Wheat GeneticsSymposium Saskatoon Saskatchewan (Eel AE Slinkarel) v2pp 17-18 (University of Saskatchewan)

Campos PE Loacutepez JR Brach AM (2005) Characterization ofpopulation ofPuccinia Irilieina in Argentina in 2003 anel 2004 In Wheat proeluctionin stresseel envirornllents Abstracts of oral anel posteI presentationsof the 7th International Wheat Conference Mar elel Plata Argentinap I29 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Chaves MS Barcellos AL Germaacuten S Scheeren PL Dei Duca LeleJASilva M Soacute e Caieratildeo E (2005) Population elynamics of PlIccilialriticilain the South Cone region of South America In Wheat proeluction instresseel envirornllents Abstraets of oral anel poster presentations [ofthe] 7th International Wheat Conference Mar elel Plata Argentinap 130 (Secretariat of Agriculture Animal Husbanelry Fisheriesanel Fooel)

Coelho ET (1980) Distritribuccedilatildeo prevaJencia de novas razas fisiologicasde PlIccilia gmlllinis tritici (ferrugem do colmo elo trigo) no Brasil ele1974 a 1978 [n Xl Reuniatildeo Nacional de Pcsquisa ele Trigo PortoAlegre RS Brasil v 2 pp 9-22 (EMBRAPA Centro Nacional elePesquisa ele Trigo Passo Funelo)

Coelho E (1982) Siacutentese elos resultaelos elas pesquisas sobre ferrugem docolmo do trigo realizaelas no Centro Nacional ele Pesquisa ele Trigo(CNPT) EMBRAPA Passo FIUlelORS Brasil 1980 e 1981 In Reunioacutenele Especialistas en Royas elel Trigo Cono Sur ele Ameacuterica INTACastelar Argentina [sp] (Programa IlCA-Cono SurBlD)

Coelho E (1986) Siacutentese elos estuelos com ferrugem elo colmo elo trigo-1982 a 1984 In Reuniatildeo de Especialistas em Ferrugens ele Cereaisele Inverno CNPTIEMBRAPA Passo Funelo RS (Eel CJ Molestina)pp 107-110 Diaacutelogo No 13 (PROCISUR Montevieleo)

Dyck PL (1989) The inheritance of leaf rust resistance in wheat cultivarsKenyon anel B Manantial Caladial JOllma of Pall Seielce 691113-1117

Dyck PL (199 j) Genetics of aelult plant leaf rust resistance in ChineseSpring and Sturely wheats Crop Scielce 24 309-311

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