Drought Tolerance Indices, their Relationships and Manner of Application to Wheat Breeding Programs (original) (raw)

Terminal moisture stress in irrigated wheat farms causes a significant reduction in quantity and quality of grain yield in Iran. In order to identify wheat varieties tolerant to late season shortage of water, and also to find how drought resistance indices should be applied in screening practices, this study was performed in a temperate region wheat breeding program of Iran for irrigated wheat. In this study 291 advanced breeding lines and cultivars of hexaploid wheat were planted in two field trials, one under normal irrigation and another one under water deficit. The normal trial received 6 times furrow irrigation from 3 rd May until 21 st June, while the water stressed trial received only one irrigation in spring at the anthesis stage. Drought resistance indices including stress susceptibility index (SSI), tolerance index (TOL), mean productivity (MP), stress tolerance index (STI) and geometric mean productivity (GMP) were calculated for all investigated entries. Correlation coefficients among these indices were calculated and interpreted. STI and GMP were found to be the better indices than the other three for screening drought tolerant wheat varieties in breeding programs. In spite of this, the STI value was still significantly affected by higher yield in one of the normal or stressed conditions. To overcome this inefficiency a 2-step screening strategy was applied. At first grain yield in both conditions along with STI was used for clustering of evaluated genotypes to ensure grouping of genotypes based on high yield in both environments and a higher STI value. Using this method, approximately four genotype groups (A, B, C and D) were determined, which led to the selection of 50 desired genotypes. Then SSI index was used to reselect the more drought tolerant genotypes. This method led to a final selection of 33 breeding lines. This strategy is proposed to be applied in wheat breeding programs whose objective is drought tolerance.

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