Barley germplasm STARS-9577B lacks a Russian wheat aphid resistance allele at a quantitative trait locus present in STARS-9301B
Russian wheat aphid (RWA; Diuraphis noxia Kurdjumov) infestations of barley (Hordeum vulgare L.) have reduced yield and quality in the United States since 1986. Resistant germplasm lines, including STARS-9577B, have been used for cultivar development. Our objective was to map quantitative trait loci (QTL) for RWA resistance in STARS-9577B and compare them to previously mapped loci. A set of 185 F2:3 families from ‘Morex’/STARS-9577B was tested in replicated trials in the greenhouse based on a 1 to 9 visual rating of chlorosis. Morex is a susceptible six-rowed malting barley. Polymerase chain reaction–based markers polymorphic between STARS-9577B and Morex were used to create a 146 marker linkage map. Quantitative trait loci analysis located two loci for resistance, one on the short arm of chromosome 1H and the other on the long arm of 3H. The 1H locus was associated with a B-hordein marker, showed additive gene action, and explained 19% of the variation. The 3H locus was associated with marker EBmac0541, showed partial dominance and explained 47% of the variation. Combined, the two loci explain 55% of the phenotypic variation for RWA reaction. Results showed that STARS-9577B lacks a resistance allele at one of the QTL found in STARS-9301B, which may explain the consistently higher RWA score (lower resistance) of 3 in STARS-9577B versus the lower score (higher resistance) of 2 in STARS-9301B, indicating that the QTL on chromosome 2H is an important factor in determining resistance.