PATHOGENICITY VARIATIONS OFTHREE...

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8* Congress of the MedlerraneanPhytopathoioglcal Union - Agadlr- Morocco, 1990 381 PATHOGENICITY VARIATIONS OFTHREE PATHOGENS OF TOMATO AND COllON : VERTICI1 1 IUM DAH1 IAE KLEBAHN, FUSARIUM OXYSPORUMFSP. LYCOPERCISI (SACC.) SNYD. and HANS. AND F.OXYSPORUM FSP. VASINFECTUM (ATK.) SNYD. and HANS. K. ASSIGBETSE *, J. HENNI ** and C. BOISSON * Centre ORSTOM - Laboratoire de Phytopathologie - Instiiut Français de RechercheScientifique pour le Dbveloppementen Cooperation - B.P.5045 - 34032 - MONTPELLIER - CBdex 1 - FRANCE. ** Laboratoire de Microbiologie - lnstilut de Biologie - Universit6#ORAN - 255 B.P.1524 - ES SENIA - ALGERIE. BACKGROUND AND OBJECTIVES In repeated standard inoculations, V. dahliae and different formae speciales of F. uxysporum did not always have the same behaviour ; symptoms sometimes very apparent were otherwise attenuated or even absent. These results suggest a potentialvariabilityof pathogenicity in these species. The objectives of this study were to test possible variations of pathogenicity bet- ween clones and in the descendance of clones in two species, V. dahliae and f. oxysporum, causal agents of vascular diseases of tomato and cotton. MATERIALSAND METHODS Inoculations were made by dipping roots of 2 week-old seedlings of tomato and cotton in spore suspensions (adjusted at 1 O sp/ml) obtainedfrom4day-oldcultures on PDA (Lahlou et Boisson, 1984). , Three types of cultureswere used in these experiments : - subcultures of increasing age issued from a clone (monospore culture) by mycelialtransfers. - subcultures obtained by monospore culture from an aging clone. - cultures obtained by weekly mycelial transfers from the margin of the initial clone thallus. Symptoms were estimatedtwo and three weeks after inoculation : -stunting of plants - chlorosis, necrosis or wilt of leaves -browning or blackening of xylem vessels in the stem - presence of living fungus in the xylem (tested by reisolation from inoculated plants).

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8* Congress of the Medlerranean Phytopathoioglcal Union - Agadlr- Morocco, 1990 381

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PATHOGENICITY VARIATIONS OFTHREE PATHOGENS OF TOMATO AND COllON :

VERTICI1 1 IUM DAH1 IAE KLEBAHN, FUSARIUM OXYSPORUMFSP. LYCOPERCISI (SACC.)

SNYD. and HANS. AND F.OXYSPORUM FSP. VASINFECTUM (ATK.) SNYD. and HANS.

i K. ASSIGBETSE *, J. HENNI ** and C. BOISSON *

Centre ORSTOM - Laboratoire de Phytopathologie - Instiiut Français de Recherche Scientifique pour le Dbveloppement en Cooperation - B.P.5045 - 34032 - MONTPELLIER - CBdex 1 - FRANCE.

** Laboratoire de Microbiologie - lnstilut de Biologie - Universit6 #ORAN - 255 B.P.1524 - ES SENIA - ALGERIE. \

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BACKGROUND AND OBJECTIVES

In repeated standard inoculations, V. dahliae and different formae speciales of F. uxysporum did not always have the same behaviour ; symptoms sometimes very apparent were otherwise attenuated or even absent. These results suggest a potentialvariability of pathogenicity in these species.

The objectives of this study were to test possible variations of pathogenicity bet- ween clones and in the descendance of clones in two species, V. dahliae and f. oxysporum, causal agents of vascular diseases of tomato and cotton.

MATERIALS AND METHODS

Inoculations were made by dipping roots of 2 week-old seedlings of tomato and cotton in spore suspensions (adjusted at

1 O sp/ml) obtainedfrom4day-oldcultures on PDA (Lahlou et Boisson, 1984). , Three types of cultures were used in these experiments : - subcultures of increasing age issued from a clone (monospore culture) by mycelial transfers. - subcultures obtained by monospore culture from an aging clone. - cultures obtained by weekly mycelial transfers from the margin of the initial clone thallus.

Symptoms were estimated two and three weeks after inoculation :

-stunting of plants - chlorosis, necrosis or wilt of leaves -browning or blackening of xylem vessels in the stem - presence of living fungus in the xylem (tested by reisolation from inoculated plants).

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382 Congress of the Mediterranean Phyfopathobgicai Union - Agadir- Morocco, 1990

RESULTS AND CONCLUSIONS

V. dahliae - Tomato (Lahlou et Boisson , 1984 - Hadisutrisno et Boisson, 1986)

Large differences in pathogenicity were observed between subcultures ofthesame clone at different ages and between sub- clones issued by monospore isolatesfrom the same clone. This variabilityconcerned both virulence and agressivity : subclones of one clone may be highly or weakly pathogenic. We observed transformation of race 1 to race 2 and reversion from race 2 to race 1.

However, hyalin variants or Kdahliae, which were abundant in descendance of old cultures, were very stable in their pa- thogßnicity.This newmateriatisveryinter- estingforfurtherstudies in physio-or histo- pathology and for the plant breeder.

F. oxysporum f.sp. lycopercisi- Tomato

In all inoculation tests, the two isolates used (originating from France and Algeria alwaysshowed the same pathogenicity on two varieties of tomato : Supermarmande (susceptible to fusariosis) and Marmande RF (resistant to fusariosis). Large variabi- lity appeared in the morphology but it had no relation with pathogenicity.

E oxysporum f.sp. vasinfectum - Conon

1989). (SOUOP, 1987 - ASSIGBETSE, 1988,

The same results were obtained with iso- lates of F. oxysporum f.sp. vasinfectum originating from Ivory Coast, Centrafrican Republicand Paraguay : the pathogenicity on susceptible cotton was always high. However, two non-pathogenic subclones

appeared three yea& ago, in the centrafri- can Republicoriginating isolate. Theywere subcultured by mycelial transfers and monospore isolation and periodically ino- culated to cotton. During this prolonged study, the pathogenicity appeared someti- mes very high and sometimes very low without apparent rule.

In conclusion, the pathogenicity of V. dahliae is demonstrated to be very varia- ble. Opposite to this result, the pathogeni- city of the two formae speciales of F. oxysporumused in ourstudy seemedvery stable except for two clones of F. oxysporum fsp. vasinfectum. These re- sults have perhaps to be compared to the specificity of the three pathogens? V. dahliaeis Ubiquist and ableto attack many different plants. F. oxyspofum f.sp. vasinfectum which is normally pathogen on cotton and okra '(Hibiscus esculentus) can occasionally in field, attack Medicago sativa and tobacco (Nicotiana tabaccum). F. oxysporumf.sp. lycopercisiis pathoge- nic only to tomato.

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REFERENCES

ASSIGBETSE K., 1988. Etude de la variabilit6 intra- cionale du pouvoir pathogene et de ia morphologie dans la desœndance par micrownidies de trois isolats de Fusarium oxyspcrum f.sp vasinfectum. agent causal de la fusariose du Cotonnier. MQ- moire de Dipl6me d'Agronomie Tropicale du CNEARC, 62p.

ASSIGBETSE K., 1989. ENde de ia variabillt6 spon- tanee chez le Fusarium oxysporum f.sp.vasinfecrum, agent de la fusariose du Coton- nier. Wmoire de DEA, option phytopathologie, Universite Paris XI. Centre d'ORSAY. 23 p.

HADISUTRISNO B. et BOISSON.. 1986. intradonal variablllty of Vertid//ium dahlias. 4th International Vertidlllum Symposlum. AoGt 1986, University of GUELPH, Ontario, Canada.

,

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i the centrafri- 3te.Theywere ransfers and iriodically ino- his prolonged .eared someti- mes very low

ienicity of V. be very varia- he pathogeni- Jeciales of F. {seemedvery :Iones of F. ~ m . These re- mpared to the athogens? V. oattack many oorum f.sp. ally pathogen IS esculentus) ack Medicago na tabaccum). :Mis pathoge-

la variabilit6 intra- de la morphologie oconidles de trois f f.sp vaslnfectom, J Cotonnier. MQ- l ie Tropicale du

la varlablllt6 spon- im oxysporum sariose du Coton- I phytopathologie, ISAY. 23 p.

,1986. Intradonal L 4th International I

986, University of

8Ih Congress of the Medterranean Phylopathological Union - Agadir- Morocco, i990 383

LAHLOU H. et BOISSON C., 1984.Variabilit6Intracio- naie du pouvoir pathogene du Verridllium albo- atrum R. et B., forme,& miaosdQrotes, vis-&-v~s de la Tomate. Les coiloqLles de l'INRA, 261, 69-78.

SOUOP D., 1986. Etude de la variabillt6 intradonale du pr?moir pathogene et de la morphologie dans la descendance par microconidies de quatre isolats du Fusarlum oxysporum f.sp. VasinfeLYum, agent causal de la fusariose du Cotonnler. MQmoire de Dipiame d'Agronomie Tropicale du CNEARC. 42 p.

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VASCULAR PATHOGENS

- Dr. J.H, Hllton.

School of Biological Science.. University of Vales,

Singleton Park, Swanaea SAZ 8PP. -

Dr. Richard Shattock. School of Biological Sciences,

UnLversity of Vales. Bangor *

Gwynedd U 5 7 2W.

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