Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) has caused significant losses to wheat and barley in many parts of the world. Two RWA resistant lines with flat leaves were crossed with each other and with two RWA susceptible lines producing rolled leaves when infested with RWA. F1, F2 and BC1F1 seedling leaves were classified according to their leaf shape as flat, longitudinally folded, or rolled after artificial infestation. Leaf chlorosis in the phenotypes of F2 plants was also recorded.
The F2 populations of flat×rolled crosses segregated in 9:3:4 (flat:folded:rolled) ratios, suggesting a two dominant gene model for control of leaf shape. Folded leaves appeared only in F2 seedlings. The F1 seedlings of flat×flat cross showed only flat leaves, while the F2 population segregated in a 13:3 (flat:rolled) ratio. Chlorosis ratings and leaf shape scores of F2 seedlings were not independent. F2 seedlings with lower chlorosis scores were more likely to have flat leaves; however, some susceptible F2 seedlings also had flat leaves. Resistant F2 seedlings may have rolled leaves. It was concluded that recording leaf shape is not a reliable visual rating method to evaluate host plant response to RWA, because the inheritance of resistance and leaf shape in wheat are under two different gene systems.