evaluation of physiological indices for improving water deficit tolerance in spring safflower

in order to evaluate the physiological indices in relation to the screening of spring safflower genotypes for drought tolerance and productivity, seed and oil yields and yield components were measured for five genotypes including local arak, local esfahan, sina, kh23 – 57 and goldasht. the study was conducted in a loam soil in east azarbaijan, iran, during three successive years (2005-2007). water treatments consisted of non-stressed and water deficit imposed from flowering (80% flowering) to maturity. several physiological indices including relative water content (rwc), stomatal conductance (kl), leaf temperature, osmotic adjustment, and specific leaf weight (slw) were measured. considering the significant decrease of seeds in capitulum, 1000 seeds weight, harvest index (hi), seed and oil yields due to water deficit, it seems that drought decreased seed and oil yields mainly via declining these components of yield. since rwc and kl decreased and leaf temperature, osmotic adjustment, and slw were increased significantly by water deficit, therefore these indices could reflect the stress effects during seed filling period. among rwc, kl, leaf temperature and osmotic adjustment, significant correlations were seen. also significant positive correlations were found among kl, rwc and slw with seed and oil yield. screening spring safflower genotypes by the abovementioned characteristics may lead to economically acceptable yields under water deficit condition. among the genotypes, goldasht, with 1,412 and 358 kg ha-1 seed and oil yields, respectively, had the lowest yield, associated with lower values of rwc, kl and osmotic adjustment. other genotypes had similar seed and oil yields, while local arak had the higher amounts of seed and oil yields, associated with higher values of rwc, kl and osmotic adjustment. it is concluded that local esfahan, sina, kh23-57, and especially local arak genotypes, can be used for cultivation in khosro shahr and areas with similar climate (cold and semi-arid in koppen climate classification) under normal and late season drought conditions.