GENETIC-ANALYSIS OF CARBON-ISOTOPE DISCRIMINATION AND AGRONOMIC CHARACTERS IN A BREAD WHEAT CROSS

Carbon isotope discrimination (Delta) has been suggested as a selection criterion to improve transpiration efficiency (W) in bread wheat (Triticum aestivum L.). Cultivars 'Chinese Spring' with low Delta (high W) and 'Yecora Rojo' with high Delta (low W) were crossed to develop F-1, F-2, BC1, and BC2 populations for genetic analysis of Delta and other agronomic characters under well-watered (wet) and water-stressed (dry) field conditions. Significant variation was observed among the generations for Delta only under the wet environment. Generation x irrigation interactions were not significant for d. Generation means analysis indicated that additive gene action is of primary importance in the expression of Delta under nonstress conditions. Dominance gene action was also detected for Delta, and the direction of dominance was toward higher values of Delta. The broad-sense and the narrow-sense heritabilities for Delta were 61% and 57% under the wet conditions, but were 48% and 12% under the droughted conditions, respectively. The narrow-sense heritabilities for grain yield, above-ground dry matter, and harvest index were 36%, 39%, and 60% under the wet conditions and 21%, 44%, and 20% under dry conditions, respectively. The significant additive genetic variation and moderate estimate of the narrow-sense heritability observed for Delta indicated that selection under wet environments should be effective in changing Delta in spring bread wheat.