VII Simposio Internacional de Trigo

1. Advances in the Research to Achieve
Resistance to Wheat Rusts
Sukhwinder-Singh, Ravi Singh, Julio Huerta, Sridhar
Bhavani and Sybil Herrera
Global Wheat Program, CIMMYT

2. Outline of the Presentation
 Introduction
 Background on resistance to wheat rusts
 Characterization of resistance
 Utilization of APR
 Mapping/ QTL analysis

3. Present (2011) vs. Future (2025)
 P o p u la t io n 6 . 8 b illio n
8 . 5 b illio n
 C onc e rn lim it e d r e s o u r c e s
e ne rg y a nd
e n v ir o n m e n t a l
c o n s u m e r p re fe re nc e
 C rop a re a L im it e d s c o p e o f
i nl a n te b rse e d i n g i n t h i s n e w e r a s h o u l d
P c r a e
b e m o r e d i v e r s i fPerd s s u r e o n l a n d w i l l
i e
iP l a nrt e a ese e i n g
nc Br d N e w t o o ls o f b io lo g y

4. Wheat Research Efforts – CIMMYT
 Increase wheat productivity - genetic gain
 Protection – biotic and abiotic stresses
(estimated global losses due to pathogen
in wheat is 13 billion dollar (~12%)
Simultaneously evaluating for Yield (Y) and
Stress Tolerant (ST)

5. Wheat Rusts – Historic Relevance
to Agriculture Productivity
Brown (leaf) rust Black (stem) rust Yellow (stripe) rust
(Puccinia triticina) Puccinia graminis Puccinia striiformis
An epidemic -
Susceptible varieties
Jupateco 73 in
Northwest Mexico Yield losses up to 100%
1976–1977. Yield
reductions up to 40%.

6. Types of Resistance
More than170 rust R genes - cataloged in wheat
1. Seedling:
 Monogenic ≈ Race-specific ≈ Major genes ≈
Vertical ≈ Hypersensitive ( Boom & Bust)
2. APR:
 Polygenic ≈ Race-nonspecific ≈ Minor genes
≈ Horizontal ≈ Slow rusting/ Partial (Durable)

7. Boom-and-Bust cycle - Northwestern
Mexico
Variety Resistance gene Released Breakdown Race
Bread Wheat:
Yecora 70 Lr1, 13 1970 1973 ?
Tanori 71 Lr13, 17 1971 1975 ?
Jupateco 73 Lr17, 27+31 1973 1977 TBD/TM
Genaro 81 Lr13, 26 1981 1984 TCB/TB
Seri 82 Lr23, 26 1982 1985 TCB/TD
Baviacora 92 Lr14b, 27+31 1992 1994 MCJ/SP

8. Genes involved in APR, 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

9. Durable Resistance
 Resistance which has remained effective in a
cultivar during its widespread cultivation for
a long sequence of generations or period of
time in an environment favorable to a
disease or pest (Johnson 1988).
 Example: Frontana, Pavon 76, Parula, and
Chapio,

10. Identification and characterization of
slow rusting resistance
● High or susceptible infection type in the seedling
growth stage
● Lower disease severity or rate of disease progress
in the field compared to susceptible check
Brown rust: High (compatible) infection type in the field
Yellow rust: Infection type not a reliable criteria due to
systemic growth habit
Stem rust: Variable size of pustules- bigger near nodes

11. Breeding for durable, adult-plant resistance at CIMMYT
Mexico (Cd. Obregon-Toluca/El Batan)- Kenya International Shuttle Breeding:
a five-year breeding cycle)
Cd. Obregón 39 masl
High yield (irrigated), Water-use efficiency,
Heat tolerance, Leaf rust, stem rust (not Ug99)
Njoro, Kenya 2185 masl
El Batán 2249 masl Stem rust (Ug99 group)
Leaf rust, Fusarium Yellow rust
Toluca 2640 masl
Yellow rust
Septoria tritici
Fusarium
Zero tillage
● Shuttle breeding between Mexico and Kenya initiated in 2006
● >1000 F3/F4 populations undergo Mexico-Kenya shuttle
● High yielding, resistant lines from 1st cycle of Mexico-Kenya shuttle
under seed multiplication for international distribution in 2010

12. Evaluation and characterization of
resistance-Field trials
 Artificial
epidemics
 Rust Severity (%): Modified Cobb Scale, Peterson
et al. 1948)
 Reaction: R, MR, MS, S

14. Borlaug Global Rust Initiative
A multi-institutional partnership for systematically
reducing vulnerability of global wheat crop to wheat rusts
Durable Rust Resistance in Wheat Project- Objectives
 Planning for the Threat of Emerging Wheat Rust Variants
 Advocating and Coordinating Global Cooperation
 Tracking Wheat Rust Pathogens
 Supporting Critical Rust Screening Facilities in East Africa
 Breeding to Produce Rust Resistant Varieties
 Developing and Optimizing Markers for Rust Resistance
 Reducing Linkage Drag
 Discovering New Sources of Rust Resistance
 Exploring Rice Immunity to Rust

15. Methodology used for identifying APR
to Ug99 in current wheat materials
● Field evaluation of advanced
breeding lines in Kenya/Ethiopia
● Greenhouse seedling tests for
susceptibility to Ug99 at USDA-ARS
Lab. in St. Paul, Minnesota, US
● Characterization of pseudo-black
chaff phenotype and application of
Sr2 molecular marker
● Identified APR Sources: Kingbird,
Kiritati, Juchi, Pavon, Parula,
Picaflor, Danphe, Chonte
Kingbird-the best source of APR

16. Genetic basis of resistance
 Evaluation of populations created from crosses:
Susceptible parent X resistant parent
Number resistance Number of genes conferring resistance
Resistant parent1 X Resistant parent2
Allelism test
Estimation of genetic diversitya
 Traditional Mendelian Segregation analysis
 Quantitative methods (formula for estimation of number of
genes determining a quantitative trait)

17. APR genes identified
 Lr34/Yr18/Pm38/Sr57/Ltn1
 Lr46/Yr29/Pm39/Ltn
 Sr2/Yr30/(Lr27)/Pbc
 Lr67/Yr46/Pm?/Sr55/Ltn
 Lr68/Yr?
Yr36

18. Leaf tip Necrosis and Slow Rusting
Resistance
 Lr34/Yr18/Pm38, Leaf tip necrosis associated with Lr46
Lr46/Yr29/Pm39 and
Lr67/Yr46/Pm? linked to
some level of leaf tip
necrosis expression
 Slow rusting resistance
without leaf tip necrosis
also known
Lalbahadur+Lr46 Lalbahadur

19. Durable adult-plant Pseudo black-chaff
resistance (APR) to stem rust
Sr2-Complex
(Sr2 and other minor genes)
• Sr2 transferred to wheat from ‘Yaroslav’
emmer in 1920s by McFadden
• Sr2 is linked to pseudo-black chaff
• Sr2 confers only moderate levels of
resistance (about 30% reduction in disease
severity)
• Adequate resistance achieved when Sr2
combined with other unknown genes
• Essential to reduce/curtail the evolution of Sr2 present Sr2 absent
Ug99 in East Africa and other high risk
areas

20. Genetic basis of durable resistance to rust diseases of wheat
% Rust
100 Susceptible
80
1 to 2 minor genes
60
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

21. Methodology
 Phenotyping: field s eas ons
A rtificial epidemic s
Rus t s everity rec orded when 80-100% dis eas e on mos t
s us ceptible RILs
 G enotyping: DA rT and S S R markers
 QTL analys is :
- IC IM)
- Q-gene
1 2 3 4 5 6

22. Molecular markers for durable
resistance
Gene Marker Reference
Sr2/Yr30 gwm533 Crop Sci 43:333–336
Lr34/Yr18 CSLV34+ Lr34sp TAG 119:889–898
Lr46/Yr29 CSLV46G22*
Lr67/Yr46 gwm192, gwm165 TAG 122(1):239-249,
Lr68 7BLNRR* TAG 124:1475–1486
Yr36 Barc101, Gpc-B1 Science 23:1357-1360
Yr48 EST BE495011 TAG 123:143-157

23. Advances in Molecular Mapping of Slow
Rusting Resistance Genes
● Several Genomic locations (QTLs) known
● Developing and characterizing mapping populations that segregate
for single resistance genes
 Single gene based populations for 2 or 3 undesignated genes now
available at CIMMYT
 Very difficult to characterize populations segregating for minor
genes that have relatively small effects
● Gene-based markers for relatively larger effect slow rusting genes
becoming reality
 Gene Lr34/Yr18/Pm38 cloned and gene-based marker available
 Significant progress made towards cloning of Lr46/Yr29/Pm39

24. Cloning rust resistance genes in
wheat
Understanding the structure of the genes and function of proteins
Major resistance genes:
Lr1(Cloutier et al)
Lr10(Feuillet et al)
Lr21(Huang et al)
APR durable resistance genes:
Lr34/Yr18 (Krattinger et al) –ABC transporter
Yr36(Fu et al) –Kinase Start gene

25. APR pleiotropic resistance gene Lr34/Yr18/Pm38
Perfect marker for Lr34
-veLr34sp & +veLr34spA
ABC (ATP Binding Cassette) (multiplex)
transporter of PDR (Pleiotropic
Drug Resistance) subfamily
Cloning of Lr34/Yr18/Pm38 1 2 3 4 5 6
● Single gene based fine mapping populations • Lalbahadur
● Gamma-ray induced deletion stocks • Lalbahadur+Lr34
• Thatcher
● Azide-induced mutations • RL6058 (Thatcher+Lr34)
● Precision phenotyping • Chinese Spring (+Lr34)
• Lr34 deletion mutant
● Partnership (CIMMYT, CSIRO and Univ. of Zurich)
Krattinger et al. Science 2009

27. Acknowledgement
DRRW : BGRI GWP at CIMMYT
(Bill and Melinda Eric Eugenio Lopez’s
Gates Foundation) Sybil Herrera-
Foessel
Syngenta Pawan K. Singh
Foundation Velu Govindan
Thank you