QTL analysis of resistance to the rice blast pathogen in barley (Hordeum vulgare)

Barley is compatible with the rice blast pathogen (Pyricularia oryzae Cav.) . Fiftyfour barley cultivars of diverse geographic origin and pedigree were inoculated with three isolates of the rice blast pathogen. All barley geno types showed blast disease symptoms when inoculated at the seedling stage w ith each of the three isolates. However, one genotype showed quantitative r esistance to all three isolates and three genotypes showed quantitative res istance to one or two of the isolates. By inoculating a set of doubled-hapl oid lines derived from the cross 'Harrington' (susceptible) and 'TR306' (re sistant) with isolate Ken 54-20, we mapped quantitative trait loci (QTLs) d etermining seedling stage blast resistance. At all QTLs, TR306 contributed the resistance alleles. The four QTLs, when considered jointly, explained 4 3.6% of the phenotypic variation in blast symptom expression. A comparison of the blast resistance QTLs with other disease resistance QTLs reported in this population revealed a region on chromosome 4 (4H) with multiple disea se resistance loci. It will be useful to capitalize on the syntenic relatio nship of rice and barley and to integrate information on species-specific r esistance genes with information on the reaction of the two species to the same pathogen.