Ravi Singh CIMMYT Mexico

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

2. 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.

3. 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?

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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 seasons
Toluca 2640 masl
Yellow rust
Septoria tritici
Fusarium
Conservation 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

11. Progress in grain-yield potential of new breeding lines after one
5-year cycle (2006-2010) of selection
25
12% yield gain
Number 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)

12. 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 = 0.348
Yield & Maturity r = 0.418
Yield & Height r = 0.312

13. 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

14. 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

15. 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.

16. 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

17. 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

18. Acknowledging agencies supporting bread
wheat improvement & rust research
Bill and Melinda Gates
Foundation through: Governments
DRRW Project ICAR, India
CSISA Project USAID, USA
Harvest Plus Project USDA-ARS, USA
SDC, Switzerland
Syngenta Foundation
Farmers’ organizations:
Agrovegetal, Spain
Cofupro, Mexico
GRDC, Australia
Thank you
Patronato-Sonora, Mexico