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Disease resistance. Stem Rust Resistance.

YrR61

Background information

In 2000 stripe rust became a threatening disease of soft red winter wheat in the eastern US when new races of stripe rust appeared in southeastern USA, which were virulent to the previously effective stripe rust resistance genes Yr8 from Aegilops comosa and Yr9 from Secale cereale. Cultivar Pioneer 26R61 (PI 612153), a soft red winter wheat, has been an effective source of stripe rust resistance for several years in the eastern region of the USA.

To determine the genetic basis of the resistance Hao et al. (1) derived a single-seed descent mapping population of 178 RILs from a crossing between Pioneer 26R61, a cultivar developed by Pioneer Hi Bred resistant to stripe rust, and AGS 2000, a high yielding variety susceptible to the current prevalent Puccinia striiformis f. sp. tritici races PST-100 and PST-102 in southeastern USA. The map was constructed using 895 markers covering all 21 chromosomes.

One major QTL was found on chromosome arm 2AS, flanked by markers Xbarc124 and Xgwm359. This QTL was temporarily designated YrR61 and explains up to 56.0% of the mean phenotypic variation. Evidence suggests it is different from Yr17 (GrainGenes link - MASWheat link) derived from Triticum ventricosum, the only formally named Yr gene in 2AS. The flanking markers for YrR61 were preliminarily tested in cultivars and lines incluidng Pioneer 26R61 in their pedigrees, indicating their use usefulness as molecular markers.

Another minor QTL was also detected and designated QYr.uga-6AS. This QTL explains 6–7% of the trait variation, and probably conditions high temperature adult plant resistance.

Markers for YrR61

Primers sequences:

Xbarc124

   BARC124-F     5'- TGC ACC CCT TCC AAA TCT -3' 
   BARC124-R     5'- TGC GAG TCG TGT GGT TGT -3' 

Xgwm359

   WMS359-F     5'- AGC CGC GAA ATC TAC TTT GA -3' 
   WMS359-R     5'- TTA AAC GGA CAG AGC ACA CG -3' 
Touchdown PCR conditions (2):
  • Denaturing step: 94°C, 3 min
  • Touchdown cycles (decrease 1°C/cycle for 15 cycles):
    • 94°C, 45 sec
    • 65-50°C, 50 sec
    • 72°C, 55 sec
  • Amplification cycles (30 cycles)
    • 95°C, 40 sec
    • 50°C, 40 sec
    • 72°C, 40 sec
  • Extension step: 72°C, 5 min
PCR reaction mix
  • 250 nM of each primer
  • 0.2 mM of each deoxynucleotide
  • 1.5 mM MgCl2
  • 1 unit Taq polymerase
  • 50100 ng template DNA
Expected products:

The products of PCR amplification were separated in a 6% (w/v) polyacrylamide gel running at 260 V. Since the validation of these markers in a larger germplasm planel is currently underway, the inclusion of check lines with and without YrR61 is highly recommended.

The fragment sizes below were determined with an ABI 3730 Analyzer (informaiton kindly provided by Gina Brown Guedira and Sharon Williamson).

Xbarc124
  • Pioneer 26R61, 215 bp
  • AGS2000, 249 bp
  • 217-260 bp fragments were also observed, indicate susceptible alleles
Xgwm359
  • Pioneer 26R61, 218 bp
  • AGS2000, 212 bp
  • 162-220 bp fragments also observed, indicate susceptible allel

Conditions presented here should be considered only as a starting point of the PCR optimization for individual laboratories.

References

1.Characterization of a major QTL for adult plant resistance to stripe rust in US soft red winter wheat. Hao Y, Chen Z, Wang Y, Bland D, Buck J, Brown-Guedira G, Johnson J. In: Theoretical and Applied Genetics, 2011, 123:14011411. DOI: 10.1007/s00122-011-1675-8.

2. Pm23: a new allele of Pm4 located on chromosome 2AL in wheat.Hao Y, Liu A, Wang Y, Feng D, Gao J, Li X, Liu S, Wang H. In: theoretical and Applied Genetics, 2008, 117:1205-1212. DOI: 10.1007/s00122-008-0827-y.

3. A microsatellite map of wheat . Röder MS, Korzun V, Wendehake K, Plashke J, Tixier MH, Leroy P, Ganal MW. In: Genetics, 1998, 149:2007-2023. [Journal link]


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