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Disease resistance. Stripe Rust Resistance.

Yr16 and QTL QYr.ufs-2A

Background information

Stripe rust was first observed in South Africa in 1996, its spread extended in 1997 and the disease became endemic two years later (1). To date four different pathotypes developed, each with enhanced virulence. In consequence, genes that previously showed resistance were rendered ineffective.

Capelle-Desprez (Vilmorin-27/Hybride-du-Joncquois) is a French cultivar released in 1946. At that time it had complete resistance to stripe rust. Even today it is considered a valuable source of both adult plant (APR) and seedling resistance genes. Capelle-Desprez carries seedling resistance genes Yr3a and Yr4a on chromosome 1B and 6B, respectively. In addition, two APR loci were proposed, Yr16 (2) and a 5BS-7BS translocation (3). However, this cultivar likely contains more stripe rust APR genes.

Capelle-Desprez was first tested in South Africa in 1998 and since then it showed excellent stripe rust resistance. Breeding line Yr16DH70 was the result of a cross between Capelle-Desprez and the susceptible South African cultivar Palmiet (SST3*//Scout*5/Agent). Yr16DH70 lacks both Yr3a and Yr4a but it retained the APR phenotype of Capelle-Desprez.

QTLs and markers

To better understand the APR features of Yr16DH70, Agenbag et al. (4) crossed this line to Palmiet to develop a recombinant inbred line mapping population. Four QTLs were found, one presented a major effect and three others had smaller effects, and they explained between 33.6 and 75.2% of the phenotypic variation.

The major effect QTL, QYr.ufs-2A, was found in every experiment and it was located on chromosome arm 2AS flanked by DArT marker loci wPt-733314 and wPt-0003. The QTL peak mapped between SSR Xgwm636 and DArT wPt-0003. This QTL explained up to 53.2% of the variation observed for disease severity and 47.8% of the variation in area of leaf infection.

One of the smaller effect QTLs (QYr.ufs-2D) mapped on the short arm of chromosome 2D, corresponding to the likely location of the previously gene Yr16, and it was flanked by SSR locus Xgwm102 and DArT locus wPt-664520.

The other two smaller-effects QTL were designated QYr.ufs-5B and QYr.ufs-6D.

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

References

1: Establishment, distribution, and pathogenicity of Puccinia striiformis f. sp. tritici in South Africa. Boshoff WH, Pretorius ZA, Van Niekerk BD. In: Plant Disease, 2002, 86:485-92. DOI: 10.1094/PDIS.2002.86.5.485.

2: Genetic analysis of chromosome 2D of wheat. Worland AJ, Law CN. In:  Zeitschrift fur Pflanzenzüchtung, 1986, 96:331–345.

3: The control of adult‐plant resistance to yellow rust by the translocated chromosome 5BS‐7BS of bread wheat. Law CN, Worland AJ. In: Plant Breeding, 1997, 116:59-63. DOI: 10.1111/j.1439-0523.1997.tb00975.x.

4: Identification of adult plant resistance to stripe rust in the wheat cultivar Cappelle-Desprez. Agenbag GM, Pretorius ZA, Boyd LA, Bender CM, Prins R. In: Theoretical and Applied Genetics, 2012, 125:109-20. DOI 10.1007/s00122-012-1819-5.


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