Deciphering the genetic component of resistance to wheat stripe rust in barley

A plant may be considered a nonhost of a pathogen if all known genotypes of the species are resistant to all known isolates of a pathogen species. However, if a small number of genotypes are susceptible to some known isolates of a pathogen species this plant maybe considered a marginal host. Barley (Hordeum vulgare L.) is a marginal host to wheat stripe rust (Puccinia striiformis f. sp. tritici) (PST). To further elucidate the genetic components of this resistance a cross was made between Abed Binder 12 (resistant) and Russell (permits hyphal growth, but not pustule formation). The parents, F1 and 97 F2 plants were inoculated with PST race 08/501 at the seedling stage and phenotyped both micro- and macroscopically. Phenotypic distributions suggested the presence of a single dominant gene, with potentially minor effect QTL modifying resistance. A genetic map was built using 548 markers from the barley oligonucleotide pooled assay and composite interval mapping identified a major QTL on chromosome 7H, provisionally designated Rpst2. Simultaneously, a small effect QTL was observed on chromosome 3H that confounded the mendelisation of Rpst2. F2:3 families segregating for Rpst2 but harbouring the susceptible allele at the 3H QTL were selected and screened at seedling stage using PST isolate 08/21. Mendelisation, fine mapping and eventual cloning of this resistance locus will provide a unique insight into inappropriate host resistance and successful transfer of these genes to wheat may open up a hitherto untapped genetic resource for resistance to PST in wheat.

Poster was presented at the UK Monogram conference in 2013 April 18-19.