CIMMYT breeding strategies and methodologies to breed high yielding, yellow rust resistant bread wheat

germplasm

Yellow (stripe) rustPuccinia striiformis

Brown (leaf) rustPuccinia triticina

Black (stem) rustPuccinia graminis

R. P. SinghJ. HuertaS. A. HerreraS. BhavaniP. K. SinghG. VeluS. Singh

Int. Yellow Rust Conf., ICARDA, Syria, 19 April 2011

Recent yellow rust epidemics: failure of our ability to respond to an early warning

Culprit gene: Yr27- a perfect example of “Boom-and-Bust” Races withYr27 virulence existed for a long time in Africa, Asia, Middle

East and America (at least 30 years based on CIMMYT database)

The famous Yr9 virulent race from East Africa that caused major epidemics in 1990s lackedYr27 virulence and suppressed older races.

Races combining virulences toYr9 and Yr27 emerged in various regions in late 1990s and early 2000s rendering some of the major varieties susceptible.

Further complications with the spread of new aggressive races adapted to warmer temperatures and prevalence of numerous susceptible varieties.

Despite various warnings to reduce areas planted under susceptible varieties- no action taken.

Result: Widespread epidemics, crop losses, lack of seed of resistant varieties, refuge in chemical control.

Discussion around the successful utilization of race-specific resistance genes

● Information on the virulence diversity and its utilization in selection and testing

● Predicting the next change in virulence and preparing germplasm: pre-emptive breeding

● Availability and ability to develop and deploy combinations of effective, diverse race-specific resistance genes

● Ability to replace susceptible varieties in a timely manner as soon as new virulence is detected

Should we continue depending on race-specific resistance genes in breeding?

Alternative approach: up-scaling research, breeding and deployment of race-nonspecific

(slow rusting or durable) adult-plant resistance

● Tall and improved semidwarf wheats with various levels of APR to all three rusts known

● Progress made in understanding the genetic basis and genetic diversity of resistance to all three rusts

● Some of the key slow rusting, multi-pathogen resistance genes now identified and gene-based, or tightly linked, molecular markers available

● One slow rusting gene cloned

● High-yielding wheat germplasm with high level of APR to all three rusts becoming a reality

Genes involved in durable, slow rusting resistance to rust diseases

Minor genes with small to intermediate effects

Gene effects are additive

Resistance does not involve hypersensitivity

Genes confer slow disease progress through:

1. Reduced infection frequency

2. Increased latent period

3. Smaller uredinia

4. Reduced spore production

Slow rusting resistance genes

● The four catalogued genes confer resistance to multiple pathogens

Yr18/Lr34/Sr?/Pm38 on chromosome arm 7DSYr29/Lr46/Sr?/Pm39 on chromosome arm 1BLYr30/Sr2/Pm? on chromosome arm 3BSYr46/Lr67/Sr?/Pm? on chromosome arm 4DL

● APR QTLs at various other genomic locations known● Single slow rusting genes usually confer inadequate

resistance under high disease pressure● Better understanding of GxE required● Yellow rust- race-specific APR genes with small to

intermediate effects also present

CIMMYT Strategy: breed durable resistance to rust diseases based on combinations of slow rusting genes

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

Relatively few additive genes, each having small to intermediate effects, required for satisfactory disease control

Near-immunity (trace to 5% severity) can be achieved even under high disease pressure by combining 4-5 additive genes

Pyramiding slow rusting genes to achieve near-immunity

Selection under uniform epidemics in field conditions is the best available method at present and the near future

An example of most recently bred wheat materials at CIMMYT under BGRI umbrella (2006-2010)

● Launch of GRI (now BGRI) in 2005● Donors initiated support in 2006● Breeding goals- Develop wheat germplasm with:

>5% higher yields than current popular varieties in target environments

Resistant to Ug99 (and derivatives) with special emphasis to incorporate durable APR

Resistant to prevalent races of yellow rust and leaf rust Appropriate grain characteristics and end-use quality

● About 800 Crosses made in 2006 utilizing Ug99 resistant sources (identified in 2005) and high yielding materials

Mexico (Cd. Obregon-Toluca/El Batan)- Kenya International Shuttle Breeding: a five-year breeding cycle) initiated in 2007 to achieve BGRI goals

Cd. Obregón 39 maslHigh yield (irrigated), Water-use efficiency, Heat tolerance, Leaf rust, stem rust (not Ug99),

Toluca 2640 maslYellow rustSeptoria triticiFusariumConservation agriculture

El Batán 2249 maslLeaf rust, Fusarium

Njoro, Kenya 2185 maslStem rust (Ug99 group)Yellow rustF3/F4 or F4/F5 for 2 seasonsAdvanced lines for 2 seasons

Crossing initiated in 2006 for stem rust resistance breeding High yielding, resistant lines from 1st cycle of Mexico-Kenya shuttle

under seed multiplication for international distribution in 2011

Progress in grain-yield potential of new breeding lines after one 5-year cycle (2006-2010) of selection

<60 60-65 65-70 70-75 75-80 80-85 85-90 90-95 95-100

100-105

105-110

110-115

115-120

0

5

10

15

20

25

Grain yield (% Checks)

Nu

mb

er

of

En

trie

s (

%)

0.6%

2009-104956 entries

2004-054814

entries

8.9%Attila, Kauz

12% yield gain

Grain-yield performance of 728 entries retained for multi-environment performance testing in 2010-2011

85-90 90-95 95-100 100-105 105-110 110-115 115-1200

5

10

15

20

25

30

35

40

Grain yield (% Checks mean)

Nu

mb

er

of

en

trie

s (

%)

39.3%(286 entries)

11.1% (80 entries)

Heading: 73-102 daysMaturity: 121-142 days

Yield & Heading r = 0.348Yield & Maturity r = 0.418Yield & Height r = 0.312

Derived from 322 crosses

Attila, Kauz

Yield potential gains in new germplasmHighly quantitative genetic control of yield

● Refinement of breeding scheme Optimizing the number of crosses and population sizes Single-backcross approach for targeted improvementSelected bulk scheme for handling large numbers of plants

in segregating populationsLarge numbers of head rows/individual plants derived F6/F7

Yield testing of large number of advanced lines

Maximizing the probability of identifying rare transgressive segregants combining high

yields with other traits

Yield potential gains in new germplasm● Diversity from 1st generation derivatives of

synthetic hexaploids● Utilization of Th. elongatum segment carrying

Sr25/Lr19 resistance genes ● Enhanced biomass and kernel weight● Increased water-use efficiency and heat tolerance● Maturity shifting towards earliness even though a

range of maturity retained

0-1 5 10 15 20 30 40 500

102030405060708090

100Mexico

Kenya

Yellow rust severity (%)

No

. o

f en

trie

s (%

)

Yellow rust resistance of 728 bread wheats in Toluca and Kenya 2010

>90% high yielding lines immune or highly resistant with APR in about 40% lines

Severity of susceptible checks =100S (N)

Races in Mexico and Kenya are virulent on Yr27 and several other important resistance genes including Yr31 present in

Pastor and its derivatives. Further testing underway in Ecuador.

Ug99 Stem Rust Resistance in 728 Wheat Lines Njoro, Kenya 2010

Adult plant resistance Stem rust Entries     Entries

Category severity (%) No. %   R-genes No. %

Near-Immune Resistant 1 120 16.5 Sr25 17 2.3

Resistant 5-10 178 24.5 Sr26 9 1.2

Resistant- Mod. Res. 15-20 199 27.3 SrTmp 49 6.7

Moderately Resistant 30 63 8.7 SrHuw234 1 0.1

SrSha7 19 2.6

Mod. Res.- Mod. Sus. 40 34 4.7 SrUnknown 5 0.7

Moderately Susceptible 50-60 27 3.7

Mod. Sus.- Susceptible 70-80 5 0.7

Susceptible 90-100 2 0.3        

Conclusion● Deployment of varieties with near-immune levels of slow

rusting, adult-plant resistance will be key for a long term genetic control of rusts

● Triple rust resistant (APR) lines with >10-15% higher yields than popular varieties and appropriate end-use quality are available

● Need to implement strategies for faster release and adoption of new, superior lines in target countries to enhance productivity and food security

● Continuous financial resources are needed for genetic control of yellow rust and other rust pathogens

Acknowledging agencies supporting bread wheat improvement & rust research

Bill and Melinda Gates Foundation through: DRRW Project CSISA Project Harvest Plus Project

Syngenta Foundation

GovernmentsICAR, IndiaUSAID, USAUSDA-ARS, USASDC, Switzerland

Farmers’ organizations:Agrovegetal, SpainCofupro, MexicoGRDC, AustraliaPatronato-Sonora, Mexico

Thank you