Abstract
BaYMV resistance genes, rym5 and rym3, were pyramided using esterase isozyme genes (Est1-Est2-Est4), whose loci had been reported to be tightly linked with rym5. BaYMV reaction was also evaluated in the field contaminated with BaYMV strain I (to which cultivars with rym5 and rym3 are resistant) or III (to which cultivars with rym5 is susceptible). Malting barley cultivars having rym5 with esterase isozyme pattern Ca-null-Nz (Mokusekko-type) were crossed with the cultivars having rym3 with Pr-Fr-Su (Prior-type). Selection of resistant lines in the field contaminated with BaYMV I with the esterase isozyme genotype of Pr-Fr-Su (Prior-type) gave lines with rym3. Selection of resistant lines in the field contaminated with BaYMV III with esterase isozyme genotype of Ca-null-Nz (Mokusekko-type) gave lines pyramided with rym5 and rym3, in which the crossing-over rate was about 4.9%. During the selection by agronomic characters, the frequency of rym3 was lowered significantly.
