To introduce powdery mildew resistant mlo alleles to Japanese barley breeding, we studied the nucleotide polymorphisms of the flanking regions of the Mlo gene and the applicability of om markers developed from foreign mlo cultivars. Within three flanking regions (a total of 1799 bp) of the Mlo gene, a total of 33 SNPs and In/Del variations were found among 35 Japanese cultivars/lines and 3 foreign mlo cultivars, Alexis, Chariot, and Pallas (mlo-5). By the combination of these variations, the cultivars were classified into eight haplotypes (A to H). Japanese cultivars had no specific variation against the three foreign mlo cultivars, but two specific SNPs different from Alexis and Chariot (types A and B) were found among Japanese cultivars/lines. Among the three foreign mlo cultivars, Chariot had an advantage as a mlo resistant allele donor in Japanese barley breeding, since it had a unique SNP, which was distinguished by an om6 marker against all Japanese cultivars/lines. As for the om2 marker, the three mlo cultivars had an insertion against type H Japanese cultivars/lines, which are mainly composed of two-row ones. The effectiveness of om2 marker selection for mlo powdery mildew resistance was confirmed by F₂ analysis derived from the cross between Alexis and Haruhimeboshi. The powdery mildew response (resistant/susceptible) of all 80 F₂ plants cosegregated with om2 marker genotypes. From these results, we showed the usefulness of om2 and om6 markers in introducing mlo powdery mildew resistant genes in Japanese barley breeding.

View full abstract