Breeding Stem Rust Resistant Wheat to Combat the Threat

from Ug99

Ravi P. Singh

Breeding Stem Rust Resistant Wheat to Combat the Threat

from Ug99

Ravi P. SinghRavi P. Singh

ICARDAICARDA

Stem Rust: the Dreaded Disease

● Caused by Puccinia graminis tritici

● Linear relationship in grain yield losses and disease severity, i.e. total losses under heavy epidemic

● Under control in most regions except East Africa since Green Revolution

Genetic Control of Stem Rust

A great success story that resulted from:● Epidemiological studies● Identification of diverse sources of resistance● Strong breeding emphasis● Germplasm exchange ● International cooperation

Detection of Race Ug99 of P. graminis in Uganda during 1999

First report of virulence for alien resistance genes Sr31and Sr38 in combination with almost all resistance genes of wheat origin (Pretorius et al. 2000 Plant Dis. 84:203)Presence in Kenya realized in 2002 although Kenyan data indicate that it may have existed since 1999Detected in Ethiopia in 2003Confirmed to be present in Yemen and Sudan in 2006Most leading cultivars and breeding lines are susceptible

Migration routes towards South Asia based on predominant wind patterns and historical precedent

2006

2003

1999

2006

2006: Detection of a new variant of Ug99 with virulence for gene Sr24

Global Rust InitiativeAverting the threat from stem rust race

Ug99 (TTKS) and its variants by systematically reducing genetic

vulnerability of current wheat cultivars

ICARDAICARDA

Race-specific genes that confer moderate to high levels of resistance in field to race Ug99

● Sr13, 14, 22, 24, 25, 26, 27, 28, 29, 33, 35, 36, 39, 40, 43, 44, 45, SrTmp, Sr1A.1R, SrSha7

● Most of the effective genes were transferred to wheat from alienspecies and genera

● Virulence in other races known for Sr13, 14, 24, 27, 28, 36, Tmp● Immediate value: Sr22, 25, 26, 35, 1A.1R and Sha7; and to a

lesser extent Sr13, 14, 24, 36 and Tmp● Agronomic effects of genes in other translocations need to be

determined and sizes of some translocations need shortening● Sr24 no longer effective to the new variant of Ug99 detected

during 2006 screening

Breeding strategy for enhancing the longevity of race-specific resistance

● Only a few race specific resistance genes available for immediate use

● Race-specific resistance genes used singly have short life (a new virulence can be detected every 4-5 years)

● GRI promotes the use of effective race-specific resistance genes in combinations to enhance their longevity

● Molecular markers are essential to ensure that multiple genes are selected simultaneously

Achieving non-race specific adult plant resistance: Ultimate goal

● Durable

● Additive, minor genes, hence difficult to select

● Limited knowledge on genetic basis of resistance for stem rust (last publications by Knott in early 1980s)

● No molecular markers, except for gene Sr2

● Sources with adequate levels of adult-plant resistance identified in recent CIMMYT and other germplasm

Top Priority: Restoring Sr2-Complex(Sr2 and other minor genes for

durable resistance to stem rust)• Transferred to wheat from ‘Yaroslav’ emmer

in 1920s by McFadden and linked to pseudo-black chaff

• Continues to confer moderate levels of resistance in Kenya (about 30% reduction in disease severity)

• Acceptable levels of resistance achieved when combined with other unknown genes

• Formed the basis of durable resistance historically in CIMMYT wheats

Sr2-based resistance Susceptible

Genes or type of resistance in wheat lines included in the1st International Stem Rust Resistance Screening Nursery (2006-2007)

Gene/resistance Entry (No.)Sr24* (White grained) 15Sr24* (Red grained) 22Sr25 (non-yellow flour) 2Sr25 (yellow flour) 17SrSha7 (Chinese sources) 7SrSynt (Synthetic wheat derived) 4Sr1A.1R 2SrTmp 1Unknown seedling resistance 2Adult Plant (Durable) Resistance 31Sr2 (Pseudo black chaff) 71*Not effective to the Sr24 virulent variant of Ug99

Grain yield performance (six sites means) of seven stem rust resistant entries included in the 2nd EBWYT (Elite Bread Wheat Yield Trial) in Northwestern India,

2006-2007

Grain Yield % over Stem rustEntry No. CID SID Cross Name kg/ha check reaction/gene*

501 61665 1 LOCAL CHECK 4560.1 100.0 -509 448408 146 WBLL1*2/BRAMBLING 4744.1 104.0 APR-MR510 448409 130 WBLL1*2/KIRITATI 4722.1 103.6 APR-MR514 414815 55 OASIS/SKAUZ//4*BCN/3/2*PASTOR 5041.5 110.6 Sr25519 448392 50 BABAX/LR42//BABAX*2/3/VIVITSI 5333.9 117.0 SrTmp+Sr2521 448400 62 WAXWING*2/KIRITATI 5202.4 114.1 APR-MR527 343315 143 HPO/TAN//VEE/3/2*PGO/4/MILAN/5/SSERI1 4699.0 103.0 APR-MR528 448422 100 PFAU/WEAVER*2//KIRITATI 4616.9 101.2 APR-RMR

LSD 295.2CV (%) 9.5

*APR = Adult plant resistance, RMR = Resistant-moderate levels, MR = Moderately resistant. Sr25 and SrTmpare race-specific resistance genes and Sr2 is adult plant resistance gene.

Genes or type of resistance in wheat lines for inclusion in the 42ndIBWSN and 29thESWYT (2008-2009)

EntriesType of resistance/ resistance gene No. %Adult Plant Resistance:5% severity (Highly resistant) 3 110% severity (Resistant) 9 315-20% severity (Resistant-Moderately Resistant) 65 1930% severity (Moderately Resistant) 77 2240-50% severity (Moderately Susceptible) 112 3360-100% severity (Susceptible) 31 9

Race-specific Resistance:Sr25 26 8SrND643 14 4Sr33 3 1SrPrinia 3 1

Total 343

Core Priorities of the Irrigated Spring Bread Wheat Improvement Program of CIMMYT

● Grain yield potential and yield stability● End use quality● Water and nutrient use efficiency● Heat tolerance● Durable resistance to rusts and other

diseases● Adaptation to zero-tillage

Application of Durable Resistance to Leaf and Stripe Rusts Extended to Stem Rust Resistance Breeding

Susceptible

1 to 2 minor genes

2 to 3 minor genes

4 to 5 minor genes

% Rust

Days data recorded

100

80

60

40

20

00 10 20 30 40 50

Breeding Approach to Incorporate Durable Stem Rust Resistance in CIMMYT Spring Wheats

● Simple, three-way and single backcrosses of high yielding wheats with best sources of adapted semidwarf adult-plant resistance sources (e.g. Kingbird, Tarachi/Kiritati, Kiritati, Juchi, Pavon, etc.) or other unadapted sources (tall Kenyan cultivars, Chris, etc.).

● Intercrosses of high yielding semidwarf wheats with high or intermediate levels of adult-plant resistance.

● Large population sizes in the segregating generations (selected-bulk scheme) and shuttling of breeding materials between Mexico and Kenya where at least two generations from F3 to F5 selected under high stem rust pressure.

● Final stem rust resistance testing of advanced lines in seedlings and for two seasons in the field before distributing internationally.

0

5

10

15

20

25

<6060-6565-7070-7575-8080-8585-9090-9595-100100-105105-110110-115

Grain yield (% Kambara )

% L

inesSingle back cross Traditional

N = 4088N = 726

0.8% > Check

10.7% > Check

Cd. Obregon 2004-2005

Grain yields of wheat lines developed through traditional (Simple and 3-way crosses) and single-backcross approach

Conclusion: Wheat Breeding Perspective

● Near-term control of stem rust is evident through the utilization of genes from wheat and its relatives

Traditional breeding to accumulate sufficient minor genes in high yielding wheatsMolecular assisted breeding to combine 2 or more effective

race-specific genes● However, how to keep these genes together in

subsequent breeding cycles remains a challenge.● Can sufficient effective race-specific or race-

nonspecific genes be cloned and inserted in a translocation for linked inheritance?

Screening of GermplasmService to anyone interested to evaluate wheat cultivars and germplasm

Kenya (KARI field site) during 2005: 4000+, and during 2006: 10,000+

Ethiopia (EARO field site) during 2005: 2000+, and during 2006: 2,000+

Outcome: Cultivars, advanced breeding lines and other sources of resistance identified in materials provided by various countries.

Frequency of resistance to Ug99 race of stem rust pathogen in wheat germplasm and cultivars of various countries, ICARDA and CIMMYT, Kenya 2006

Response and frequency Percent

Country Resistant Mod. Res. Mod. Sus.-Sus. Res.+Mod. Res.

Argentina 11 7 32 36.0

Bangladesh 0 3 81 3.6

Caucasus 8 6 88 13.7

China 1 1 116 1.7

Chile 2 6 62 11.4

Egypt 3 0 146 2.0

India 161 7 79 22.5

Iran 3 1 106 3.6

Khazakstan 171 9 192 11.9

Nepal 1 1 103 1.9

Pakistan 0 6 99 5.7

Russia 0 1 34 2.9

South Africa 71 41 123 52.3

Turkey 291 15 293 13.1

WANA Varieties from ICARDA 0 13 164 7.3

ICARDA nurseries 20 72 1182 7.2CIMMYT nurseries 155 71 660 34.2

Total 337 260 3560 14.41 Some of the lines are durums and triticale.

Genes or type of resistance in wheat lines for inclusion in the2nd International Stem Rust Resistance Screening Nursery

Type of resistance/ resistance gene Entries (No.)Adult Plant Resistance:Resistant-Moderately resistant (15-20% severity) 48Moderately resistant (30% severity) 100

Race-specific resistance:Sr25 2Sr26 3SrTmp 34SrSha7 1Unknown genes 7

Total 195