Genetic mapping of resistance to Rhynchosporium commune and characterisation of early infection in a winter barley mapping population

The genetic basis of resistance to Rhynchosporium commune was investigated in a winter barley mapping population derived from a cross between cultivars Saffron (moderately susceptible) and Retriever (moderately resistant). Resistance was assessed in field trials through total infection (measured using qPCR), and visible disease symptoms. Phenotypic correlations between both methods of assessing disease severity were high. QTL mapping from three years of field trials identified five significant QTL effects. One QTL effect on chromosome 2H confirms a previously reported resistance from a population derived from the spring cultivar Cocktail and a winter parent derived from the cultivars Pearl and Cocktail. Another QTL effect on 3H corresponds to the reported position of major resistance gene Rrs1 . An effect was detected at the mapped position of the semi-dwarfing gene sdw - 1 despite the fact that neither parent has the semi-dwarf phenotype. Of the remaining two QTL effects, one on 6H may represent a previously reported rhynchosporium resistance (QTL Triton Rrs6H 271 ), whilst the final QTL, represents a novel resistance. In addition, interactions during early infection stages in the parental lines were studied by confocal microscopy of detached leaves inoculated with a GFP-expressing R. commune isolate. This approach identified a number of major differences in fungal growth morphology between the resistant and susceptible parent.