Gene Action and Selection Grain Yield Response for and Morpho-Physiological Yield Components in Spring Wheat

The present research programme includes studies on gene action, combining ability, heterosis, and heritability for grain yield and morpho-physiological yield components from F₁ and F generations of a diallel cross involving 9 varieties of spring wheat. Detailed gene actions for yield and yield components were studied in four selected crosses. Relationships between grain yield and yield components were studied in the diallel crosS, Fa and BlF (Biparental Intermating Progenies) of the four crosses. This also ineludes study on responses to selection for grain yield and yield components in F.a on F generation. In both Fi and Fa generations of the diallel cross, additive and nonadditive gene actions were involved in controlling spikes per plant, grains per spike, 100-grain weight, plant height, biological yield and grain yield. Grain yield and biological yield were predominantly controlled by nonadditive gene action, while other were mainly controlled by additive gene action. Study of GCA (General Combining Ability) effects suggests that Jaral, Sonalika and Nobre were good general combiners for grain yield and some of the yield components. These parents had good agronomic performances. There were also a good number of crosses having significant estimates of both SCA (Specific Combining Ability) effects and heterosis in F₁ and F generations. The heterosis of the crosses in Fi generation was positively correlated with the genetic divergence between their parents. All characters including grain yield were highly heritable in broad sense. In narrow sense, spikes per plant, grains per spike, 100-grain weight, plant height and harvest index were medium to highly heritable. But biological yield and grain yield were poorly heritable. Gene actions studied in the four crosses showed differences in genetic control of the characters among the crosses. In Nobre/Kalyansona, there was significant estimates of additive gene action for grain yield. In Nobre/Condor and Janak/Sonalika, grain yield was mainly controlled by dominance gene action. Taichung 29/Fima 77 indicated presence of duplicate epistasis for grain yield and other yield components. Study of relationships between yield and yield components in a diallel cross suggests that biological yield and harvest index were most important yield components. Other characters, spikes per plant, grains per spike, 100-grain weight and plant height contributed to grain yield indirectly through biological yield and harvest index. Correlation studies in Fas and BlPs suggest that yield components were related to grain yield through their developmental relationships. But primary yield components were related between themselves through linkage effects in both coupling and repulsion phases. Responses to selection in Fa generation over Fa of the four crosses suggest that direct selection for grain yield was more efficient than indirect selection through yield components. These findings indicated that selection in spring wheat for high yield can be kept limited to direct use of grain yield as a parameter.