Stripe rust resistance in the UK winter wheat cultivar Claire

Stripe rust resistance in the winter wheat cultivar Claire has remained effective in the UK and Europe since its release in 1999. To characterise this valuable source of resistance a cross was made between Claire and the stripe rust susceptible cultivar Lemhi, producing F2:3 and doubled haploid (DH) populations. A genetic linkage map was constructed using SSR, AFLP, DArT and NBS-AFLP markers that had a total map length of 1730 cM. To improve the definition of the two QTL identified on the long arm of chromosome 2D EST-derived markers were developed from EST mapped to the 2D terminal deletion bin, 2DL 0.76-1.00. Stripe rust resistance was evaluated on adult plants under field and glasshouse conditions by measuring the extent of fungal growth, Percentage infection (Pi) and the necrotic/chlorotic response of the plant to infection, Infection Type (IT). Four QTL contributing to stripe rust resistance were identified in Claire, QPst.claire-2Da, QPst.claire-2Db, QPst.claire-2B, and QPst.claire-7B. For the Pi phenotype QPst.claire-2Da explained up to 25.4% of the phenotypic variation, QPst.claire-2Db up to 28.7%, QPst.claire-2B up to21.7% and QPst.claire-7B up to 13.0%. For IT the percentages of the phenotypic variation explained were 23.4%, 31.8%, 17.2% and 12.6%, respectively. Examination of DH lines carrying QPst.claire-2Db identified variation in the Pi phenotype, lines either showing a highly resistant phenotype or an intermediate resistant Pi value. This led the authors to propose the possibility of a suppressor, originating from Lemhi that acted specifically towards the QTL QPst.claire-2Db. In addition to the four QTL conferring stripe rust adult plant resistance (APR) in Claire, a race-specific, seedling expressed resistance gene was identified on chromosome 3B which is no longer effective against UK pathotypes of the stripe rust fungus Puccinia striiformis f. sp. tritici.