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Abstract
Selection for drought tolerance typically involves evaluating genotypes for either high yield potential or stable performance under varying degrees of water stress. Field Studies were conducted in 1992 and 1993 to assess methods for evaluating genotypes with combined high yield potential and stability, in both years, 12 spring wheat (Triticum aestivum. L.) genotypes were grown under two irrigation levels (well-watered and stressed) imposed between tillering and anthesis with a line-source sprinkler irrigation system. Drought susceptibility index (the ratio of the yield of genotype in drought to the yield of the same genotype in well watered conditions standardized by the mean yield of all genotypes in drought and well watered conditions) and relative yield (yield of an individual genotype under drought divided by the yield of the highest yielding individual genotype in a population under drought) values were used to describe yield stability and yield potential of the 12 spring wheat genotypes. There were year-to-year variations in drought susceptibility index (DSI) and relative yield (RY) values within genotypes and changes in genotypic rankings within years. The DSI values ranged from 0.42 to 1.24 in 1992 and from 0.51 to 1.59 in 1993. The mean RY were 0.79 and 0.86 in 1992 and 1993, respectively. The DSI did not provide a good indication of yield potential as some genotypes has DSI < 1 but RY lower than average under water-stressed conditions. The RY (higher than average) under water stress was a good indicator of yield potential of a genotype per se but gave no indication of yield stability. The plots of DSI vs. RY values were found useful in identifying genotypes with high yield potential and relatively stable yield performance under different moisture regimes.