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2nd International Wheat Stipe Rust Symposium Izmir, Turkey, May 2014
H-J Braun, RP Singh, J Huerta-Espino, SA Herrera-Foessel, C Lan & BR Basnet
Global status of yellow rust on wheat and strategies for its short and long term control
Trace to 100% yield losses depending on the time of the epidemic initiation, susceptibility of variety & climatic conditions
Selection of virulence for resistance genes Yr9and Yr27 associated with epidemics in the last 25 years in Africa, Middle East and Asia
Worldwide spread of aggressive, temperature tolerant races and their further evolution:
new areas, initiation of epidemics at earlier growth stages and higher severity
Fungicide application becoming a routine in some countries
Global status of yellow rust
The good news:
More productive spring, facultative and winter
wheat germplasm, resistant to current yellow
rust (and other rusts) populations has been
distributed through various international yield
trials and nurseries, and also developed by
various National Programs during past years
Various yellow rust resistant varieties released
in different countries
Immediate action points:
Reduce the area sown to susceptible varieties
by promoting new varieties with diverse
resistance
Release and seed multiplication of resistant
varieties in countries lagging behind
Release and promotion of additional varieties
with complex resistance base
If not done then in 3rd YR conference we will assemble & discuss the same again
Long-term R4D for a sustainable yellow rust control (1)
Surveillance of pathogen population for a timely detection
of new virulences of relevance
Trap nurseries (NILs and varieties)
Race characterization (GRC-Denmark, Turkey/ICARDA in Izmir,
India, Pakistan, Iran, China, Mexico, USA, Australia, etc.)
Information on the resistance genes present in commercial
varieties and important breeding materials
Gene postulation, molecular mapping- robust diagnostic
markers
High-throughput markers assays
Long-term R4D for a sustainable yellow rust control (2)
Identification of new resistance genes and their utilization
Race-specific genes- large & small effect; seedling & adult-plant
Slow rusting, pleiotropic adult-plant resistance genes
Breeding more productive wheat varieties
Utilizing race-specific effective resistance genes in combinations
(preferably 3 genes per combination)
Strong molecular breeding approaches for a forward breeding
Utilizing multiple minor, slow rusting genes, or their combination
with small/intermediate effect race-specific genes
Field based selection in conjunction with other traits
Fungicides are part of the solution
Reality with the utilization of large effect race-specific genes
● Most often end up being used as a single gene –stewardship / stacking
● Molecular breeding being practiced only in some programs but often results in non-competitive varieties
● Few effective genes with reliable molecular markers available at present
● Stronger emphasis required for marker assisted pyramiding of genes together with forward breeding approaches including genomic selection
Breeding minor, slow-rusting genes based adult plant resistance in combination with small/intermediate effect race-specific resistance genes for achieving near-immune resistance
from seedling growth stages
● Resistance based on 4-5 slow rusting APR genes is usually adequate in areas where yellow rust infection initiates from stem elongation stages onwards (APR genes are already functioning by then)
● However, with the aggressive races of yellow rust- infection in some areas initiates as early as tillering stage when APR genes still not fully functional
● Utilize combinations of slow rusting APR genes with small/intermediate effect race-specific resistance genes that have enhanced expression due to additive effects
Pleiotropic multi-pathogen resistance: a subclass of adult plant resistance genes
● Lr34 [ Syn. = Yr18=Sr57=Pm38 =Ltn1=Sb1= Bdv1]
chromosome 7DS
(leaf rust, yellow rust, stem rust, powdery mildew, leaf tip necrosis, spot blotch, barley yellow dwarf virus )
● Lr46 [ Syn.= Yr29=Sr58=Pm39=Ltn2=Ts?]
chromosome 1BL
● Lr67 [Syn.= Yr46=Sr55=Pm46=Ltn3]
chromosome 4DL
Formation of cell wall appositions (instead of hypersensitivity with race-specific genes)
Start0.0
Xgwm49769.7XksuH9c70.4XksuG34b72.5
End131.4
start0.0Xwmc1474.8
Centromere99.5
End204.0
Xgwm2106.4Xbarc12414.9Xwmc154a28.5Xgwm148b61.2Xbarc1884.5Xwg99687.0Xglk40087.8Xbarc13b88.8Centromere95.6Xwmc245b98.1Xpsr92499.7Xbarc124a101.3Xbarc230103.6Xbarc167105.0Xgwm120112.7Xpsr540117.0XwPt-6278121.9Xwmc175b126.5Xwmc332134.2End172.2
Start Xwmc1110.0Xgwm2619.1Xcfd5310.0Centromere22.0Xgwm10229.2Xwmc19043.9XwPt-372852.2Xgwm53953.9
Xgwm34983.6Xgwm30192.0Xgwm320 End95.0
Start0.0Xcfd3630.3Xgwm359b52.2Xgwm122a56.3Centromere88.4Xcfa2263102.7Xsfr.BE590525a133.1Xwmc170152.1
End213.5
Start0.0XwPt-78902.9Xbarc31023.0Centromere49.3Xpsr59854.0Xpsr57058.4Xpsr54360.9
End170.1
Start0.0
Xfba9189.4Xfba24190.0Xbcd1532104.1XksuA6109.3Xbarc125121.4Xgwm456133.1Centromere156.4End226.6
Start0.0
Centromere29.2
gwm742 gwm83288.2gwm16088.9End103.2
Start0.0Centromere9.0gwm54010.1wmc23811.9gwm49517.0gwm16519.9gwm36822.1gwm14923.0
End70.7
Start0.0
glk42459.1Centromere60.9barc15185.3Vrn197.2Xfbb209.1105.0Xabg391110.0gwm126117.7End133.5
Start0.0Centromere34.5gwm63955.3wmc415a56.8gwm49959.6
End158.5
Start gwm4590.0gwm3343.8
wPt-095942.5Centromere45.7wPt-706358.8wmc256b69.9barc377.4gwm617107.7gwm427111.2End112.0
Start0.0
Centromere75.0
bcd1510120.4ksuD27134.8End149.5
Start Xgwm4710.0wPt-8149 wPt-41727.0gwm66618.2fba12751.8Xwmc28375.7barc17485.5cfa217491.2Xbarc10899.9Centromere104.1
End207.0
Start0.0gwm935c57.0gwm57357.9gwm4661.6gwm4367.5Centromere69.0psr35086.8psr129a88.3pwir23297.4psr59398.1gwm131103.0wmc273a106.4ksuD2116.3gwm146a119.8gwm146b133.0wmc273b134.4psr680b136.9gwm344b142.8barc182143.5gwm577156.6End190.7
Chromosome 1A
Chromosome 7DChromosome 6DChromosome 5DChromosome 4DChromosome 3D
Chromosome 7BChromosome 6BChromosome 5BChromosome 4BChromosome 3BChromosome 2B
Chromosome 7AChromosome 6AChromosome 5AChromosome 4AChromosome 3A
Chromosome 2D
Chromosome 2A
Chromosome 1D
Chromosome 1BStart0.0Xpsr94943.0Centromere45.1Xgwm60454.4Xgwm18a55.3Xgwm1160.8Xgwm27361.7glk48363.2Xgwm13168.5Xgwm268117.4Xwmc44159.5Xgwm793173.0
Lr46/Yr29/Sr58/Pm39
Start0.0Xcfd6626.9XwPt-332841.7Xgwm29552.2Xgwm13055.0XcsLV3456.4Xbcd143859.1Xgwm1002a59.5Xwmc405b79.2Xgwm1002b80.3Centromere97.9
End227.0
Start0.0
gwm13233.0Centromere48.0barc10155.0barc13656.8gwm19361.0gwm36163.0gwm62676.6gwm21992.7End104.5
Start0.0Centromere23.4
End268.0
Start0.0
gwm16530.0Centromere30.5gwm19231.3
End84.1
Lr67/Yr46/Sr55/Pm46
Lr34/Yr18/Sr57/Pm38
Start0.0Xgwm389a2.4Xgwm533a7.6Xgwm493a20.0Xpsr91991.5Xpsr110195.5Xgwm383a150.8Xgwm131b179.7XwPt-0036198.4Xbcd131212.6Xgwm299c270.4Xgwm340301.1End306.4
Sr2/Yr30
Diversity for Yellow Rust QTL (marked in yellow): > 35 regions through consensus maps(Rosewarne et al. TAG 2013, 126:2427-2449 )
Examples of small/moderate effect race-specific resistance genes characterized recently at CIMMYT and
their interaction with slow rusting genes
● Yr54 in Quaiu3 on 2DL
● YrF in Francolin on 2BS
● YrSuj in tall variety Sujata on 7BL
● Yr60 in Lalbahadur on 4AL
Contrasting example: A race-specific gene with minor effect in seedlings but immunity in adult plants:
● YrKK in tall variety Kenya Kudu on 2BS
APR QTL interaction in enhancing yellow rust resistance of Avocet x Quaiu3 RILs
Yr29 Yr30
Yr54
Minor QTL
Yr29+Yr30+3D QTL
Yr29+Yr30+3D QTL+Yr54
Source: Basnet et al. Plant Dis. 2013
Moderately effective race-specific gene YrF on 2BS and slow rusting genes
together confer a high level of YR resistance in Francolin#1
Other APR genes/QTL• Lr46/Yr29 on 1BL• Yr30/Sr2 on 3BS• Two additional minor QTL
PVE: 10.3–21.1%
Source: Lan et al. (2014) Mol. Breed. DOI 10.1007/s11032-014-0075-6
Francolin#1 is an improved CIMMYT semidwarf & shows high level of resistance to yellow rust- 50% severity when YrF present alone
Race-specific gene YrSuj on 7BL and slow rusting APR genes together
confer a high level of resistance in Avocet/Sujata mapping population
Other APR genes/QTLLr46/Yr29 (PVE:5.6-6.2%)Lr67/Yr46 (PVE: 6.9-10.7%)QYrLr.cim-7BL (PVE: 11.7-20.9%)QYr.cim-1AS (PVE: 5.7-8.9%)QYr.cim-3DS (PVE: 6.3-8.2%)
Sujata is an improved tall variety from India & shows high level of resistance to yellow rust- 40% severity when YrSuj present alone
Source: Lan et al. (unpublished)
Future: GM intervention to achieve resistance durabilityGene Cassettes- multiple resistance genes inherited as a single unit:
simplifying breeding and enhancing resistance durability
Lr34/Yr18 Yr36 Lr21
SynR1 SynR2 SynR3
Natural gene cassette(currently developed)
Synthetic gene cassette(future possibility)
Natural gene cassettes currently in the pipeline at CSIROLr34/Yr18/Sr57 +Lr67/Yr46/Sr55 +Lr21 +Yr36
• Cloning many resistance genes for diversity
• Technology for insertion of large DNA “packages” – gene expression
• Synthetic R genes?
• Cisgenic vs Transgenic crops
Scientific/Commercialisation Challenges
Source: CSIRO-GRDC Triple Rust Initiative
Conclusions Sustainable yellow rust control will require growing resistant
varieties in disease prone areas around the world
Wheat varieties should be enriched with multiple pleiotropic APR genes, representing a novel class of resistance to rusts and other wheat pathogens, to curtail/slow down pathogen evolution
Although near-immune level of durable resistance to all three rusts can be achieved through field selection, molecular markers can aid better utilization & diversity
New approaches, such as “resistance gene cassettes” could further expedite breeding for durable rust resistance
Fungicides should be part of the rust control strategy
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