CIMMYT breeding strategies and methodologies to breed high yielding, yellow rust resistant bread wheat germplasm
CIMMYT breeding strategies and methodologies to breed high yielding, yellow rust resistant bread wheat germplasm Yellow (stripe) rust Brown (leaf) rust Puccinia striiformis Puccinia triticina R. P. Singh J. Huerta S. A. Herrera S. Bhavani P. K. Singh Black (stem) rust Puccinia graminis G. Velu S. SinghInt. Yellow Rust Conf., ICARDA, Syria, 19 April 2011
Recent yellow rust epidemics: failure of our ability to respond to an early warningCulprit 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 diseasesMinor genes with small to intermediate effectsGene effects are additiveResistance does not involve hypersensitivityGenes 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 7DS Yr29/Lr46/Sr?/Pm39 on chromosome arm 1BL Yr30/Sr2/Pm? on chromosome arm 3BS Yr46/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 100 Susceptible 80 1 to 2 minor genes 60% Rust 40 2 to 3 minor genes 20 4 to 5 minor genes 0 0 10 20 30 40 50 Days data recorded 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-immunitySelection 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 masl High yield (irrigated), Water-use efficiency, Heat tolerance, Leaf rust, stem rust (not Ug99), Njoro, Kenya 2185 masl Stem rust (Ug99 group) Yellow rust El Batán 2249 masl F3/F4 or F4/F5 for 2 seasons Leaf rust, Fusarium Advanced lines for 2 seasonsToluca 2640 maslYellow rustSeptoria triticiFusariumConservation agriculture 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 25 12% yield gainNumber of Entries (%) 20 2004-05 2009-10 4814 entries 4956 entries 15 10 0.6% 8.9% 5 Attila, Kauz 0 <60 60-65 65-70 70-75 75-80 80-85 85-90 90-95 95-100 100- 105- 110- 115- 105 110 115 120 Grain yield (% Checks)
Grain-yield performance of 728 entries retained for multi- environment performance testing in 2010-2011 40 Heading: 73-102 days 35 Maturity: 121-142 days Number of entries (%) 30 Derived from 322 crosses 25 39.3% 20 (286 entries) 15 11.1% 10 Attila, Kauz (80 entries) 5 0 85-90 90-95 95-100 100-105 105-110 110-115 115-120 Grain yield (% Checks mean)Yield & Heading r = 0.348Yield & Maturity r = 0.418Yield & Height r = 0.312
Yield potential gains in new germplasm Highly quantitative genetic control of yield● Refinement of breeding scheme Optimizing the number of crosses and population sizes Single-backcross approach for targeted improvement Selected bulk scheme for handling large numbers of plants in segregating populations Large 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
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 100 Mexico 90 80 Kenya No. of entries (%) 70 Severity of susceptible checks =100S (N) 60 50 40 30 20 10 0 0-1 5 10 15 20 30 40 50 Yellow rust severity (%) 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.
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 researchBill and Melinda GatesFoundation through: Governments DRRW Project ICAR, India CSISA Project USAID, USA Harvest Plus Project USDA-ARS, USA SDC, SwitzerlandSyngenta FoundationFarmers’ organizations:Agrovegetal, SpainCofupro, MexicoGRDC, Australia Thank youPatronato-Sonora, Mexico