Evaluation of spring safflower genotypes by using tolerance and sensitivity indices to terminal heat stress

Introduction To plant breeding in relation to high temperature tolerance, and for determining the differences between resistant genotypes, several indices in the basis of crop yield in normal and stressed conditions were be introduced. With regard to importance of genetic breeding for higher yield and stability in exposure to terminal heat stress in warm region of Iran, and little studies about tolerance of safflower cultivars, this study was carried out by measuring tolerance and sensitivity indices. Safflower is one the most important oil crops in regions that have dry and warm winters like to Khuzestan province of Iran. This crop are relatively tolerant to environmental stresses. But it is reported there are significant differences between different cultivars. The study was conducted to evaluate the difference between safflower cultivars in Ahvaz region. Materials and Methods To comparison of safflower cultivars by indices of tolerance and sensitivity to terminal heat stress, present study was carried out in Ramin Agriculture and Natural Resources University of Khuzestan, at 2016-2017. A split plot design in the basis of Randomized Complete Blocks Design (RCBD) with four replications was used for the study. Experimental factors was included four sowing date (11 November, 2 December, 5 January and 3 February) were placed in main plots, and safflower cultivars (sina, goldasht, soffeh, Esfahan local (kooseh) and faraman) were placed in subplots. In this study, several indices with regard to researcher’s reports were calculated and used for determining the difference between safflower cultivars. Statistical analysis was done using by SAS v. 9.1 software. Results and Discussion The results of statistical analysis showed that investigated cultivars had significant differences in terms of Stress Sensitivity index (SSI), Tolerance Index (TI), Productivity Mean (PM), Harmonic Mean (HM), Yield Stability Index (YSI), (GPM), Stress Tolerance Index (STI), Stress Damage Index (SDI), and Modified Stress Tolerance for appropriate conditions (MSTI1), Modified Stress Tolerance for no appropriate conditions (MSTI2), and Yield Reduction Index (YRI). However, differences between cultivars in terms of Ranking Index (RI) and Yield Index (YI) were not significant. Therefore, STI was the best index for evaluating tolerance and sensitivity of safflower cultivars to terminal heat. On the basis of STI, most tolerate and sensitive cultivars were goldasht and Esfahan local (kooseh), respectively. Conclusion The results showed that safflower cultivars had significant differences in terms of tolerance indices calculated in the study. In the basis of Stress Tolerance Index (STI), goldasht cultivar had highest tolerance (lowest sensitivity) and local Esfahan cultivar (kooseh) had lowest tolerance (highest sensitivity) to terminal heat stress. Generally, in regions exposed to environmental stress, best cultivars are the cultivars that in normal conditions have high yield and in stressed conditions have no significant reduction f yield (group-A in Fernandez classification). In this study, stress tolerance index (STI) had good ability for determining of these cultivars. Key words: Comparison, cultivar, grain yield, sowing date, stress tolerance index