Diallel Analysis of Wheat Grain Protein Content and Yield in F1 and F2 Generations under Contrasting Nitrogen Conditions

Grain yield and grain protein content (GPC) of bread wheat are crucial determinants of its profitability and product quality. In general, low levels of nitrogen fertilizer result in a lower protein content in wheat grains and lower grain yield. The main objective of this investigation was to get information on gene action, heritability and expected genetic advance from selection (GA) for GPC and grain yield/plant (GYPP) under contrasting soilnitrogen conditions. Diallel crosses in F 1 and F 2 generations among six contrasting wheat parents in GPC and GYPP were evaluated in field experiments across two seasons in a split plot design under two N levels, i.e. low-N (0kg N/fed) and high-N (75kg N/fed). In both F 1 's and F 2 's, the magnitude of dominance (H 1 ) was much greater than that of additive (D) component for GPC under both high N and low N and GYPP under high-N, while the opposite was true for GYPP in F 1 's under low-N, where the additive was greater than dominance variance and GYPP in F 2 's under low-N, where the additive and dominance components were approximately equal. The average degree of dominance (H 1 /D) 1/2 in F 1 's was in the range of over-dominance, except for GYPP under low-N, which showed partial dominance, but in F 2 's was in the range of partial dominance for GYPP under both high and low N and GPC under high N, while GPC under low N showed no dominance. Narrow-sense heritability (h 2 n ) in F 1 's and F 2 's was generally of low magnitude; it ranged in F 1 's from 6.18% (GPC under low-N) to 20.41% (GYPP under high-N); the exception was GYPP under low-N, where h 2 n was of high magnitude (67.14%) and ranged in F 2 's from 10.86% for GPC under low N to 46.90% for GYPP under low-N. The h 2 n was higher under low--N for GYPP and under high-N for GPC. In F 1 's, the values of GA were higher under low-N than under high-N for GYPP, but were higher under high-N than low-N for GPC. In F 2 's, the values of GA for both traits were higher under low-N than under high-N, suggesting that it is better to practice selection in F 2 's for both traits under low-N conditions to obtain higher values of selection gain.