CHOOSING EVALUATION ENVIRONMENTS TO INCREASE WHEAT-GRAIN YIELD UNDER DROUGHT CONDITIONS

A key question in genetic improvement of yield under drought stress is how to choose environments to evaluate and identify genotypes that yi eld well under drought. The objective of this study was to compare var ious moisture regimes as evaluation environments for wheat (Triticum a estivum L. emend. Thell.) germplasm, based on performance of specific genotypes and on expected genetic advance from direct and indirect sel ection. The test included 12 new, experimental spring bread wheat geno types selected for high yield under both full and reduced irrigation i n Mexico and four cultivars selected in and adapted to each of the fol lowing moisture regimes: (i) full irrigation (FI), (ii) late season dr ought (LD), (iii) early season drought (ED), (iv) residual moisture (R M), and (v) sporadic drought. All genotypes were yield tested for 2 yr under four moisture regimes: (i) FI (five irrigations), (ii) LD (two early season irrigations), (iii) ED (one early and two late season irr igations), and (iv) RM (one early season irrigation). Estimates of exp ected selection response indicated that indirect selection under FI wo uld result in greater yield gains under drought than would direct sele ction in any of the drought environments. However, under all drought c onditions, certain of the new, experimental genotypes produced yields that were numerically, though not always statistically, higher than ge notypes selected only under FI. Evaluation under both optimum and drou ght conditions appears to be an effective method to take advantage of the increased selection response under FI while preserving alleles for high yield under drought.