Molecular mapping of loci conferring susceptibility to spot blotch and resistance to powdery mildew in barley using the sequencing-based genotyping approach

Spot blotch caused by Bipolaris sorokiniana and powdery mildew caused by Blumeria graminis f. sp. hordei are two important diseases of barley. To map genetic loci controlling susceptibility and resistance to these diseases in the barley cultivar Bowman and line ND5883, a mapping population consisting of 138 recombinant inbred lines (RILs) was developed from the cross between these two barley parents. Genotyping of Bowman and line ND5883 as well as the RILs by genome sequencing revealed 7,393,920 SNPs between the two parents, and 5,215 SNP markers segregated in the population. A genetic map was constructed with 852 unique SNP markers, which formed 9 linkage groups covering 1014.81 cM in length with an average marker density of 1.19 cM. Bowman and ND5883 showed distinct infection responses (IRs) at the seedling stage to the two pathotype isolates (ND90Pr and ND85F) of B. sorokiniana and one isolate (Race I) of B. graminis f. sp. hordei. Genetic analysis of the RILs showed one major gene controls the susceptibility to B. sorokiniana isolate ND90Pr and another major gene confers resistance to B. graminis f. sp. hordei isolate, respectively. The gene (Scs6) conferring susceptibility to spot blotch caused by ND90Pr was mapped on chromosome 1H of Bowman as previously reported. The gene (Mla 8) conferring resistance to powdery mildew in ND5883 was tightly linked to the Rcs6/Scs6 locus on chromosome 1H. QTL analysis identified two QTL (QSbs-1H-P1 and QSbs-7H-P1) responsible for susceptibility to spot blotch caused by B. sorokiniana isolate ND85F in ND5883, which are located on chromosome 1H and 7H, respectively. QScs-7H-P1 was mapped to the same region as Rcs5 and may represent a different allele at the same locus.