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Disease resistance. Stripe Rust Resistance.

Yr59

The spring wheat germplasm 'PI 178759' originating from Iraq carries a locus for stripe rust resistance on chromosome arm 7B that was designated Yr59.

The Yr59 locus codes for a high-temperature adult-plant (HTAP) type of resistance. At low temperature 'PI 178759' was sensitive to Puccinia striiformis f. sp. tritici races PST-17, PST-37, PST-43, PST-45, PST-100, PST-114 and PST-127 in seedling tests. The three last races are common in the United States since 2004. However, with adult plants and at high temperatures, lines carrying this gene were highly resistant, both in greenhouse and field tests over several years.

Zhou et al. (1) developed a mapping population between 'Avocet Susceptible' and 'PI 178759' using SSRs and RGAP (resistance gene analog polymorphism) markers to determine the exact location of the locus and to evaluate the levels of resistance it confers. The analysis of inheritance demonstrated the stripe rust resistance is controlled by a single gene with a partially dominant behavior. The mapping and QTL analysis indicated that Yr59 is located on the distal region of the long arm of chromosome 7B (deletion bin 7BL-0.86-1.00), flanked by SSR marker Xbarc32 and RGAP marker Xwgp5175 on an interval spanning 2.1 cM. The QTL explained between 33.7 and 40.1% of the phenotypic variation in relative area under the disease progress curve in adult plants. The phenotypic variation for the infection type data varied between 49.2 and 51.4%

An additional analysis of genetic distances and allelism tests showed that Yr59 is different from other stripe rust resistance genes also located on chromosome arm 7BL: Yr39, Yr52, YrZH84, and YrC591.

Markers for Yr59

SSR locus Xbarc32 is located on the proximal side of Yr59 at less than 2.1 cM. On the distal side the closest locus is the RGAP marker Xwgp5175. However, for the assessment of a validation panel the authors used another SSR on the distal with a higher annealing temperature, Xwmc557. This locus is some 2.2 cM away from Xwgp5175.

Primer sequences:

Xwgp5175 (2)

    rga51 5'-GGA GGC TTA GGG AAG-3'
    rga75 5'-TGG TAG GTC CTT GTA-3'  

Xbarc32

    BARC32-F 5'-GCG TGA ATC CGG AAA CCC AAT CTG TG-3'
    BARC32-F 5'-TGG AGA ACC TTC GCA TTG TGT CAT TA-3'  

Xwmc557

    WMC557-F 5'-GGT GCT TGT TCA TAC GGG CT-3'
    WMC557-F 5'-AGG TCC TCG ATC CGC TCA T-3'  

Final concentrations of the PCR mix (2)

Reaction volume: 15µl

PCR conditions (2)

PCR reactions were performed in a GeneAmp® PCR System 9700 thermo-cycler. The PCR products were separated on a 5% polyacrylamide gel and silver-stained for visualization

Expected products

Xbarc32, located proximal to Yr59, produced a 165-bp in the resistant parent and a 175-bp in the susceptible one. On the distal side, Xwgp5175 amplified a 450-bp product in PI 178759 and did not amplify on 'Avocet Susceptible'. It is important to note that this marker also amplifies on Chinese Spring. Also on the distal side, Xwmc557 amplifies a 150-bp product in PI 178759, However, it also amplifies on certain lines not carrying Yr59.

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

References

1. Identification of Yr59 conferring high-temperature adult-plant resistance to stripe rust in wheat germplasm PI 178759. Zhou XL, Wang MN, Chen XM, Lu Y, Kang ZS, Jing JX. In:Theoretical and Applied Genetics, 2014, 127:935-945. DOI:10.1007/s00122-014-2269-z.

2. Characterization and molecular mapping of Yr52 for high-temperature adult-plant resistance to stripe rust in spring wheat germplasm PI 183527.Ren RS, Wang MN, Chen XM, Zhang ZJ. In: Theoretical and Applied Genetics, 2012, 125:847-857. DOI:10.1007/s00122-012-1877-8.

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