Russian wheat aphid (RWA) is a devastating pest on barley grown in the intermountain regions of the western U.S. All barley cultivars presently in commercial production are susceptible to RWA feeding damage. Typical RWA feeding damage to the leaf results in chlorotic flecking and characteristic longitudinal white, yellow, or red chlorotic streaks with convolute rolling of the leaf. Rolling of the leaf reduces photosynthetic area, provides an optimum environment for aphid reproduction, protects the aphids from contact insecticides and natural predators, and at heading, can prevent spike extrusion, resulting in obstruction of flowering and decreased seed set.
All available accessions of Hordeum vulgare in the USDA-ARS National Small Grains Collection have been screened in the greenhouse for resistance to RWA. Thirty-eight lines have been identified as resistant and an additional 67 as moderately resistant to moderately susceptible (1). Robinson et al.(2) reported a single dominant gene for RWA resistance in barley line S 13. Genetic analysis of parents, F 1, and F2 from the cross Morex/ PI 366450 indicated multiple gene control for RWA resistance in barley accession PI 366450 (1). STARS9301B (PI 573080) is a RWA resistant selection out of PI 366450.
Crosses were made between Morex, a susceptible malting barley cultivar, and STARS-9301B. Genetic analysis was performed on parents, Fl, F2, and BC populations as well as 232 F2 derived F3 families. Segregation in the F2 and BC populations indicated multiple gene control. Thirteen F3 families were found to be homozygous resistant and 12 homozygous susceptible, indicating that two genes control RWA resistance in STARS-930113. Chi-square analysis of the F2 and BC to either parent suggested mutual epistasis between one additive gene which is more expressed, and one dorninant gene which is less expressed.