Diallel Analysis of Wheat streak mosaic virus Resistance in Winter Wheat

Wheat streak mosaic virus (WSMV) (Family: Potyviridae; Genus: Tritimovirus ), disseminated naturally by the wheat curl mite ( Aceria tosichella Keifer), is an important disease of wheat ( Triticum aestivum L. em Thell.) worldwide. Breeding for resistant cultivars remains the best strategy to control the disease. Nine winter wheat genotypes with differential reaction to WSMV were crossed in a complete diallel mating design to determine the combining ability of WSMV resistance. Parents, F 1 , and reciprocal crosses were inoculated at the seedling (2–3 leaves) stage with a WSMV‐SD isolate and evaluated for reaction under greenhouse conditions. Disease reaction was assessed twice (at 1‐wk intervals) by a 1‐to‐5 scale (1 = no visible symptoms to light green streaks, 5 = severe yellow streaks and necrosis). Data were analyzed according to Griffing's Method 3 and Model 1, where one set of F 1 and reciprocal F 1 are included. Highly significant genotype effects ( P < 0.01) were observed for WSMV resistance. General combining ability (GCA) and specific combining ability (SCA) effects for WSMV resistance were highly significant ( P < 0.01), indicating that both additive and nonadditive genetic effects are involved in the inheritance of WSMV resistance. The reciprocal effects were not significant ( P > 0.05). The ratio of combining ability variance components [(2σ 2 GCA )/(2σ 2 GCA + σ 2 SCA )] was small (0.1), indicating that nonadditive (i.e., dominance and epistasis) gene effects were more important than additive gene effects in controlling WSMV resistance in these crosses; therefore, progeny performance cannot be adequately predicted from GCA effects alone.