Evaluation of drought tolerance in an interspecific hybrid and some genotypes of safflower using drought resistance indices

This study was performed in order to evaluate the drought tolerance of some safflower genotypes in a field experiment carried out at the research farm of Isfahan University of Technology located at Lavark, Najaf-Abad, Iran (40 km south west of Isfahan, 32º 32´ N, 51º 23´ E, 1630 m asl). In this study, five genotypes including A82) interspecific hybrid), landrace Kooseh, Goldasht, C111 and Ac-stirling were evaluated in a randomized complete block design with three replications at two moisture levels (normal and 90% water-depletion), separately. Seven drought tolerance indices including Stress Tolerance Index (STI), Tolerance Index (TOL), Stress Susceptibility index (SSI), Mean Productivity (MP), Geometric Mean Productivity (GMP), seed yield in stress (Ys) and non-stress (Yp) environments were calculated for each genotype based on seed yield under stress and normal conditions. The results analysis of variance showed that there were significant differences among the genotypes for all traits. The drought stress had significant effect on head diameter, number of heads per plant, number of seeds per head, seed weight per head and seed yield. Mean comparisons showed that control genotypes were significant differences for all studied traits except seed weight per and seed yield traits with the genotype A82 under non stress and stress conditions. Principal component analysis (PCA), indicated that the first and second components justified 91% of variations between drought tolerance indices. First vector showed 67% of the variations and was recognized as yield potential component and drought tolerance indices (MP, GMP, STI) and the second rector justified 24% of total variations which would be named as “drought susceptible components (TOL and SSI indices). Biplot analysis also indicated that STI, MP, GMP were more reliable indices to identify drought tolerant safflower genotypes and discriminated Goldasht genotype and genotype A82 as the most drought tolerant. The indices STI, GMP, MP identified the Goldasht  and A82 genotype as a drought resistant genotype and this genotype was obtained from interspecific crosses between cultivated safflower (Carthamus tinctorius L.) and wild species (C. oxyacanthus). This genotype had the highest grain yield under stress and non-stress conditions. Therefore, it could be used in safflower breeding programs to improve drought tolerance.