Mapping of quantitative trait loci conferring resistance to barley yellow mosaic virus in a Chinese barley landrace Mokusekko 3

A Chinese six-rowed barley landrace, Mokusekko 3, exhibits a wide resistance spectrum to all the barley yellow mosaic virus strains in Japan (BaYMV-I, -II, -III) and in Europe (BaYMV-1, -2) as well as to barley mild mosaic virus (BaMMV). To identify the genetic basis for the resistance to BaYMV, a cross between a Japanese malting barley cultivar Ko A (susceptible) and Mokusekko 3 was made to generate F ₂ and F ₃ populations. The reaction of the F ₂-derived F ₃ lines to BaYMV was investigated in a field infected with BaYMV (-I or both -I and -II) during two growing seasons, 1996 and 1997. BaYMV disease severity of the F ₂ individuals was quantitatively expressed as the percentage of the susceptible seedlings within the F ₃ line. For the linkage analysis along the whole chromosome, a map of the barley genome consisting of 100 markers was used. The map covers 1291 cM with an average density of 14 cM. The interval mapping method was used to identify the quantitative trait loci (QTLs) for resistance to BaYMV. A new QTL for resistance to the BaYMV was located in the terminal region of chromosome 7HS, explaining 20-25% of the phenotypic variance, in addition to those in the terminal region of chromosome 3HL and centromeric region of chromosome 4H. The three QTLs accounted for 55-57% of the total phenotypic variance. The location of the QTLs on chromosomes 4H and 3HL corresponded well to that of rym1 and rym5 which were previously mapped for resistance to BaYMV in Mokusekko 3 using morphological and isozyme markers. Based on these results, the effect of pyramiding of these resistance factors into modern barley cultivars by marker-assisted selection is was examined.