Corn rusts: Common rust,

Southern rust

& Tropical rust

Wm. E. Dolezal Maize Product Development

Pioneer Hi-Bred

Johnston, IA

APS 2011 Field Crops Rust Symposium

San Antonio, TX

Dec. 14, 2011

2

Corn Rusts Presentation Outline

Basic biology & identification tips of the three common rusts found on Corn

• Tropical Rust (Physopella zeae)

• Common Rust (Puccinia sorghi)

• To be discussed in more detail by Snook Pataky in an upcoming presentation

• Southern Rust (Puccinia polysora)

Southern Rust – lack of host differential set & issues to rebuild a set

• Discussion around Robert’s 1962 differential set

• Other P. polysora host differentials in the literature

• Background on a new race detected (Rpp9 virulent race)

• Update on cooperative effort to rebuild host differentials

• Opportunities to leverage with new identification methodology.

Questions & Answers

3

The three rusts of maize

With a little practice in observing

symptoms, and the use of a

microscope, it is relatively easy

to tell the corn rust from one

another, but …….identifying the

race is occurring on the plant is a

whole different story.

4

Identifying rusts of corn

There are three rusts that infect corn

Two belong to the genus Puccinia

Puccinia sorghi: Common Rust

Puccinia polysora: Southern Rust

The third is in the genus Physopella

Physopella zeae: Tropical Rust

5

Tropical Rust – White rust of corn

Physopella zeae • Microcyclic

• Believed to autoecious

• Zea mays

• Teosinte

• Tripsacum spp.

Distribution: Americas

• Brazil – mainly in Goias but also in other areas of the high plateaus

• Mexico – mainly in Chiapas & Campeche

• USA – outbreak in 1969/1970 in FL, eradicated and not found since

Urediniospore germination:

• Free leaf moisture for 1-2 hrs. @ 22’ C

6

Tropical Rust

White pustules – small but many on a leaf

In many ways, to me, it resembles Southern Corn Rust

Often found in tropical / subtropical areas with P. polysora

Dual infection on a plant can be devastating to yield and standability

7

Tropical Rust – Pustules & urediniospores

Note: Teliospores have no

pedicel in contrast to the

two Puccinia rusts.

8

Tropical Rust – Races – How many?

Very little research being done in this area.

Most recent work from Brazil.

Historical data:

• Roberts (1962) Report • Identified PI 185054 (Turkey)

• She established two races

• PZ1 & PZ2

• M. Lima, et al. (1996) [Brazil]

• Inst. Agrononomio de Campinas

• Evaluated 440 inbreds derived from

• 8 different origins

9

Tropical Rust – Races

M. Lima et al. (1996) [Brazil]

Classes Pop.

103

Pop.

101

Taiuba Suwan-2 Diversas Pop.

102

Pop.

104

Thai.

Composite

R 9.6 7.6 13.1 3.6 10.3 3.4 11.8 0

I 24.8 44.3 21.3 46.4 41.4 27.6 29.4 8.3

S 58.6 46.8 65.6 41.1 41.4 58.6 58.8 83.3

AS 7.0 1.3 0 8.9 6.9 10.3 0 8.3

n 157 79 61 56 29 29 17 12

Scale 1 2 3 4 5 6 7 8 9

% infection 0 1 2.5 5 10 25 50 75 >75

Classes; R = Resistant; I = Intermediate; S = Susceptible; AS = Very Susceptible Disease Rating

Adapted from: Bragantia, Campinas, 55(2)269-273

None of the inbreds were found

to be immune to infection

10

Common Rust

Puccinia sorghi • Macrocyclic

• Heteroecious

• 30+ Oxalis species

• Zea mays

Distribution: Worldwide

Urediniospore germination:

• Range: 4 – 31’ C

• Optimal: @ 15 – 25’C

Infection: @ 6 – 12 hrs.

RH > 98% required for germination. Optimal @ 100%RH

11

Common Rust

Puccinia sorghi

12

Common Rust

Puccinia sorghi

13

Common Rust – Puccinia sorghi

• Pustules mostly on BOTH leaf surface, but usually not on husk.

• Pustules usually a reddish to reddish brown color

• Disease develops in cooler temperatures

• Urediniospores (conidia) usually are ROUND

14

Common vs. Southern Rust

15- 25’C + 25’C

Caution:

Some corn

germplasm

may show

pustules on

the upper

surface only!

Examine the

spores.

15

Often occurs in banding pattern on the leaf

Foliar reaction dependent upon host resistance factor

16

Foliar Reaction Types:

• Chlorotic flecks

• Necrotic flecks

• “Blotches” – wide range in sizes

17

Southern Rust

Puccinia polysora • Microcyclic

• Believed to be autoecious hemiform

• Zea mays

• Teosinte

• Tripsacum spp.

Distribution: Worldwide tropical & subtropical regions.

Urediniospore germination:

• Optimal: @ 23 – 28’C

Optimal Infection: 16 hrs dew period @ 26’C.

18

Southern Rust

USA:

• 1941 - First identified on corn

• 1949 – First detected in the Corn Belt

• Several well documented outbreaks in the past 60 years

• 2006 – new race (Rpp9 virulent) observed

1949 - 1950s:

• Well documented outbreaks in Africa & Asia (Philippines)

• Races first identified in Eastern Africa

19

Identifying Southern Corn Rust

“Come back to the field in

one week…if it is dead,

then you definitely had

Southern Corn Rust!”

Method 1 - Temporal

Two quick ways to determine if it is SCR

Several accounts in the

literature about how

rapidly P. polysora

can kill a crop.

20

Identifying Southern Corn Rust

1. Wear a clean white shirt and/or a

short sleeve shirt.

2. Walk a zigzag sampling pattern

through the corn field.

3. Now look at your shirt & your arms. If

they are now orange, then…you have

Southern Corn Rust!

Method 2 – Color Recognition

21

Southern Rust – Economic Damage

• Yield loss reported can be big:

• USA up to 45 – 75%

• Africa – 1950s > 50%

• Philippines 1956 > 80%

• Often it is comes in a little later in

fields with HIGH yield potential,

major stalk lodging can occur.

22

Southern Corn Rust – Identification Tips

• Pustules mostly on upper leaf surface

• Caution: occasionally you will find

some pustules develop along the

midrib on the bottom of the leaf.

• Pustules can also be on the husk.

• Pustules usually an orange to a

reddish-orange color

[Tennessee “Vol” orange]

• Disease develops in warm moist

conditions

• Urediniospores (conidia) usually

oblong, ellipsoid but most are NOT

ROUND.

• Caution:

Immature spores are round!

23

Southern Rust - Foliar Symptoms

Susceptible vs. Resistant

resistance

Susceptible foliar

reaction

24

P. sorghi (common)

P. polysora (southern)

Photo by Snook Pataky, UIUC

25

Telial Differences

Common Rust:

Teliospores produced in the

same sorus as urediniospores.

Southern Rust:

In the USA, teliospores are usually not

commonly found in the field except late

in season as the tissue starts to die.

More common in tropical regions. Often

they display a semicircular (horseshoe)

type or completely circular type pattern.

Telial stage not often seen in fields.

26

Easiest way to tell the rusts - Telial stage

P. polysora:

Short pedicels

@ ¼ length of spore

Long pedicels

@ 1-2x spore length

Contrast to P. sorghi teliospores

27

What race of

P. polysora is it?

Early race identification done in Africa

• Storey & Howland (late 1950s)

• Rpp1 & Rpp2

• Used to differentiate EA1 & EA2

Alice Robert expanded this effort (1962)

• =Rpp3 – Rpp8

The issues surrounding

race identification today

28

Race change in P. polysora 2006:

February - Goias, Brazil:

• A cooperative effort between USDA-ARS & Pioneer Hi-Bred

to screen a set of 225 maize accessions for P. polysora

resistance identified uredial formation on several Rpp9 lines. • A USDA Maize Crop Germplasm Committee Goal

August - York, NE:

• Widespread southern rust outbreak in the region. Several

Pioneer inbreds and hybrids that contained the Rpp9 gene

were observed to have some uredial formation.

2007:

February - Goias, Brazil: Similar results on Rpp9 material as in 2006.

March - Puerto Vallarta, Mexico:

• A set of Pioneer inbreds & hybrids containing the Rpp9 gene

had significant uredial development

June - Victoria, TX – a few pustules were observed on Rpp9 hybrids.

July - Cairo, GA: the same material that contained the Rpp9 had NO

observation of uredial development (no sporulation observed)

29

Rust Spore Dispersal –

Aug 2008: Tropical Depression Fay

Photo credits: NOAA

2008 Southern Rust Outbreak- GA

Collected isolates non-virulent

on hybrids containing the

Rpp9 gene

Collected isolates virulent

on hybrids containing the

Rpp9 gene

Inbreds & hybrids containing

the Rpp9 gene observed

having uredial formation.

There appeared to be mixed race

infections on leaves with some

hypersensitive (resistant) and

moderately susceptible reactions

observed on the same plant. Map source: http://quickfacts.census.gov/qfd/maps/georgia_map.html

31

31

Overcoming an old standard source of resistance

Rpp9 source of resistance has been stable for many years (20+)

The “new” race overcomes the Rpp9

The exact identity of the new race can not be positively determined, only

that it has virulence to the Rpp9 gene

The question was asked:

Why can we not determine the exact race of the fungus?

32

Isolate Place

Collected

AF

RO

5329

7/35

0

AF

RO

474

NC

13

Po

p 3

6

E30

9

Co

rnel

i 54

Flo

ury

Syn

thet

ic

CI3

8B x

Cu

zco

PI 1

6359

7

PI 1

9890

2

PI 1

8620

8

Race

EA. 1 East Africa R0 S X S S S S S S R1,2 S EA.1

EA. 2 East Africa S S S S S S S X S R1 R1,2 EA.2

Ga-2 Georgia S S X X X S S X S R1,2 R1 EA.2

Ga-3 Georgia S S S - X S S S S R1,2 R1 EA.2

Ven-1 Venezuela S S X S X S S S S R1 R1,2 EA.2

Ga-1 Georgia S R2 R1 R2 S R2 R1,2 X S R1,2 S PP.3

Nic-1 Nicaragua S S X S X S S X S R1 S PP.4

Nic-3 Nicaragua S S S S R1,2 S S S S X R1,2 PP.5

Col-1 Colombia R0 S X S S S S S R1,2 R1 S PP.6

Mex-1 Mexico S S X S X S S R1,2 S R1 S PP.7

Fla-1 Florida S S S S S X S S S X X PP.8

Nic-2 Nicaragua S S X S X S S X S S S PP.8

PR-1 Puerto Rico S X X S X S S X S X S PP.8

Robert’s Host Differential Reactions – P. polysora

R0, R1, R2 = Resistant; S and X = Susceptible From: A. L. Roberts, Phytopathology 52:1010-1012

Lines

No

Longer

Exist

Lines

No

Longer

Exist

Rpp9

Races

No

Longer

Exist

33

New Race of

Southern

Corn Rust

34

35

Host Resistance – Rpp Study

Lines evaluated for reactions to P. polysora isolates

Rpp9a Tropical Rppb Other Rpp Susceptible

PI186208 1416-1 Sure Gold B37

PI186215 1497-2 Calvary Oh43

B37 Rpp9 NC300 B1138T W64a

Oh43 Rpp9 DS61 Mo17 (poly resist)

W64a Rpp9 Va59 Mp78:62

Green Giant 1 Garrisonc

Green Giant 2 SS Jubilee Plusc

P33M52 P33M57

From: Pataky, Dolezal & Brewbaker, 2010

a = allelic with Rpp9 or resistance from PI186208 b= map to 10S c = Rp1-D but not Rpp resistant = Not Rpp9 (allelism or race specificity)

36

LinesCal Rpp Source GA isolate IL isolate

Susceptible Checks none 4 4

PI186208 (Boesman) Rpp9 4 0

PI186215 (2-687) Rpp9 4 0

Green Giant 1 Rpp9 4 0

Green Giant 2 Rpp9 4 0

P33M52 Rpp9 4 0

B1138T Rpp9 4 0

NC300 Rpp9 4 0

B37 Rpp9 Rpp9? 1 0

Oh43 Rpp9 Rpp9? 1 / 2 0

W64a Rpp9 Rpp9 2 / 3 0

1416-1 Maps 10S 2 / 1 0 / 1

1497-2 Maps 10S 1 /0 0 / 1

DS 61 Not Rpp9 2 / 1 0

Va59 Not Rpp9 1 / 2 0

Sure Gold 10S 0 0

Calvary 10S 0 0

Scale = 0-4

37

Differential Varieties Race designation

P. sorghi

P. polysora 1 2 3 4 5 6 7 8 9

1

0

1

1

1

2

1

3

1

4

1

5

1

6

S. L. P. 20 R R R R S R R R S S S R S S S S

Rp1g79-109 70-2/Q6198 R R R S R R S S R R S S R S S S

A632 11/Q6199 R R S R R S R S R S R S S R S S

67/Q6200 R S R R R S S R S R R S S S R S

Yeh’s proposed P. polysora race differentials

R = Resistant; S = Susceptible

S.L.P. 20 = San Luis Postosi 20

Q Lines are from Queensland Australia

Adapted from: C.C. Yeh. Studies on rusts of maize

Journal. of Agricultural Research Of China 35:81-93 1986.

38

Sources of Resistance – P. polysora

6 experimental hybrids were used to characterize pathogen variability.

• Among 60 isolates collected at 6 sites over two years

– 17 virulence patterns were identified

• Most frequent virulence patterns were identified.

• They were observed in all locations where sampled suggesting

the absence of geographical differentiation among the prevalent

P. polysora populations.

• Recommended more intensive analysis using

• Larger number of isolates

• Single gene differentials &/or

• Molecular markers

• No hybrid was resistant to all isolates

2002: Variability in Isolates of Puccinia polysora in Brazil C. R. Casela & A. S. Ferreira Fitopatologia Brasileira 27: 414-416

39

Sources of Resistance – P. polysora

QTLs associated with P. polysora resistance found on:

Chromosomes #s 3, 4, 9 & 10

Major gene Rpp9, found on Chromosome 10

Contrast with QTL’s associated with P. sorghi resistance found on:

Chromosomes #s: 1-10

2006: The Genetic Architecture of Disease Resistance In Maize:

A Synthesis of Published Studies R. J. Wisser, P. J. Balint-Kurti & R.J. Nelson

Phytopath. 2006 Vol. 96, No. 2, 120-129

40

Do we reconstruct the

Host Differential set for P. polysora?

Supplement it with what germplasm?

• Start with remnant lines from Robert’s 1962 List

• 6 of 11 differentials are still available

• Many vary in their maturity

• PI186208 (Boesman Yellow Flint) is a segregating source

• Retest of NCRPIS lines tested earlier in Brazil?

• Brewbaker’s lines?

• Chávez-Medina, Leyva-López & Pataky’s lines?

• Select set of GEM released lines?

41

IVP IVNO ITEM

Ames 27141 NC290A

Ames 27144 NC296

PI 639056 GEMS-0031 (XL380:S11 F2S4 2282-01 )

CUBA164:S2012-235-1-B

BR105:T33a

BR106:T33a

Ames 29394 1497-2

Ames 29448 1416-1

PI 506244 Tzi 3

PI 506245 Tzi 4

PI 540746 Tzi 14

PI 595560 CML 40

PI 186208 BOESMAN YELLOW FLINT

PI 234767 ENANO

PI 217413 Zapalote Chico

PI 445062 Narino 330

PI 506348 Suwan 2

PI 443845 Antioquia 423

PI 489361 Cuba 164

PI 483816 Cuba 117

PI 576247 Chiapas 645

PI 498498 Cuba 96

PI 593017 Hi39

Retest of

NCRPIS lines

shown

resistant

earlier testing

in Brazil?

SLP20

70-2/Q6198

71/Q6199

67-1/Q6200

Include

Yeh’s lines?

42

Supplement with what germplasm?

• Retest of NCRPIS lines? • Brewbaker’s lines?

• Chávez-Medina, Leyva-López & Pataky’s lines?

• Select set of GEM released lines?

43

Inbred Origin Avg.CIMMYTA-21 2.5

CML295 1

GT601 1

Hi34 Antigua 2.22

Hi43 SetG 1

Hi44 Suwon 1

Hi45 Suwon 1

Hi53 ICAL210 2

Hi54 ICAL221 2.3

Hi55 ICAL224 2.3

Hi56 KenyaF 2.25

Hi57 Ki9 1.38

Hi63 Pi23 1.5

Hi64 Pi31 1

Hi65 Tx601 2.83

Hi75 190 1.67

Hi76 217 1.73

ICAL219 2.25

ICAL220 1.75

ICAL223 2

ICAL36 2

INV138 2.5

Ki3 2.5

Ki18 2.5

Ki20 2.5

KP1 1

KP131 2.5

KP288 2.5

KP293 2.5

KP310 2.5

KP311 2.5

KS23-3 1

KS23-4 1

KS23-5 1

KS23-6 1

Narino 330 3

PH110-26 2.5

TZi8 1

TZi11 2.5

TZi14 2

TZmi1822 2.2

41 1.89

Inbred Origin Avg.

Brewbaker’s lines?

(Scale: 1=resistant; 9= susceptible)

44

• Retest of NCRPIS lines?

• Brewbaker’s lines? • Chávez-Medina, Leyva-López & Pataky’s lines?

• Select set of GEM released lines?

Supplement with what germplasm?

45

Rating: 0 = chlorotic-fleck reaction, no uredinia; 0.5 = very few,

very small uredinia or segregating for chlorotic fleck reactions,,,

Sources of Resistance – P. polysora

Data from

Chávez-Medina, Leyva-López & Pataky

Plant Disease: November 2007, Volume 91, Number 11

Accession rated 0:

Accession Accession Name

Ames 19016 Virginia VA59

NSL 75976 IA DS61

PI 186209 Yellow flint

PI 186215 Inbred 2-687

PI 198905 4F-374 GE3

PI 186191 Inbred 627

Accession rated 0.5:

Accession Accession Name

PI 484024 Puerto Rico 13

PI 515053 Loreto 9

PI 515055 Loreto 11

PI 515097 San Martin 126

PI 553058 OC5

PI 558524 Mo6

PI 596502 OC15

46

• Retest of NCRPIS lines?

• Brewbaker’s lines?

• Chávez-Medina, Leyva-López & Pataky’s lines?

• Select set of GEM released lines?

Supplement with what germplasm?

A number of the Germplasm Enhancement of Maize Program

released Lines contain genetic backgrounds that would suggest

a good chance of having resistance.

• They are more adapted than some PI’s in the collection.

47

Corn – Diseases: Lesion Mimics

Just to make

it a little more

interesting!

These are hypersensitive responses.

Many are believed to be mutations of

the Rp (common rust resistance)

genes and may be involved in

providing resistance to infection.

These are the examples

of the foliar expression

of specific genes…

LES genes

48

My P. polysora identification wish list:

PCRs that identify the rust race without having to grow

out the host differential plant.

Recent development: July, 2011 Plant Disease:

Real-Time PCR Detection and Discrimination of the Southern and Common Corn

Rust Pathogens Puccinia polysora and Puccinia sorghi by Jo Anne Crouch and

Les J. Szabo

Using PCRs to sample spores deposited in rain water samples,

air samplers, on leaves, etc. to monitor pathogen populations

49

Thank You – Questions on the 3 Rusts?

Tropical Physopella zeae

Southern Puccinia polysora

Common Puccinia sorghi