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 yield well under drought. The objective of this study was to compare various moisture regimes as evaluation environments for wheat (Triticum aestivum L. emend. Thell.) germplasm, based on performance of specific genotypes and on expected genetic advance from direct and indirect selection. The test included 12 new, experimental spring bread wheat genotypes selected for high yield under both full and reduced irrigation in Mexico and four cultivars selected in and adapted to each of the following moisture regimes: (i) full irrigation (FI), (ii) late season drought (LD), (iii) early season drought (ED), (iv) residual moisture (RM), 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 irrigations), and (iv) RM (one early season irrigation). Estimates of expected selection response indicated that indirect selection under FI would result in greater yield gains under drought than would direct selection in any of the drought environments. However, under all drought conditions, certain of the new, experimental genotypes produced yields that were numerically, though not always statistically, higher than genotypes selected only under FI. Evaluation under both optimum and drought 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.