Evaluation of Yield-Based Drought Tolerance Indices for Screening Safflower Genotypes

Drought tolerance is not often considered an independent trait by plant breeders because the collective result of many traits of a plant with positive or negative interactions may be fairly general and polygenic in nature. The objective of this study was to evaluate six drought tolerance indices, namely the stress susceptibility index (SSI), yield stability index (YSI), tolerance index (TOL), mean productivity (MP), geometric mean productivity (GMP), and stress tolerance index (STI), to be used in screening safflower (Carthamus tinctorius L.) genotypes. For this purpose, 64 genotypes were grown during two growing seasons (2011-2012) under both normal and drought-stress field conditions at the Research Farm of Isfahan University of Technology located at Lavark, Najaf-Abad, Iran. The drought tolerance indices were calculated based on seed yield under drought stress and nonstress conditions. Results of combined analysis of variance showed the significant influences of drought stress on seed yield as well as significant differences among genotypes for seed yield and the indices. Results of calculated correlation coefficients and multivariate analyses showed that GMP and STI indices were able to discriminate between drought-sensitive and -tolerant safflower genotypes. Cluster analysis using the drought-tolerance indices divided the 64 genotypes into tolerant and susceptible groups. Based on multivariate analyses using the indices singly or in combinations, it was possible to identify the most yield-stable genotypes across the environments. Overall, we concluded that GMP and STI indices can be efficiently exploited not only to screen drought tolerance but also to identify superior genotypes for both stress and nonstress field conditions in safflower.