Effect of irrigation withhold at different growth stages on grain yield and stress tolerance indices in three safflower cultivars

Effect of irrigation withhold at different growth stages on grain yield and drought tolerance indices in three safflower cultivars was studied in experimental field of Seed and Plant Improvement Institute, Karaj, Iran, in 2002-2004 cropping seasons. The experimental design was split plot arrangement in randomized complete block design with three replications. Drought stress levels; S1 (blooming and seed development), S2 (blooming and flowering), S3 (blooming), S4 (flowering), S5 (seed development) and S6 (control) were assigned to main plots, and safflower cultivars; Arak 2811, Isfahan local and FO2 were randomized in sub-plots. Combined analysis of variance demonstrated that the highest grain (1258 kg.ha-1) and oil (377 kg.ha-1) yields belonged to Isfahan local in non-stress conditions which was not significantly different from grain and oil yield under S5 drought stress treatment. To evaluate the responses of cultivars to drought stress, different drought tolerance indices, including Stress Susceptibility Indices (STI), Tolerance index (TOL), Mean Productivity (MP), Stress Tolerance Index (STI) and Geometric Mean Productivity (GMP) were calculated. Correlation coefficients showed strong relationship between grain yield in stress and non stress conditions as well as SSI, TOL and GMP indices. MP, GMP, and STI identified Isfahan local as tolerant, and Arak 2811 as susceptible cultivars to drought stress. TOL and SSI also confirmed that Isfahan local as tolerant cultivar for drought stress conditions.