Evaluating the Contribution of Ionic and Agronomic Components toward Salinity Tolerance in Safflower

Safflower (Carthamus tinctorius L.) is a versatile crop species that is well adapted to arid and semiarid conditions. Limited information is available on the response of safflower genotypes to salinity stress under field conditions. The objective of this study was to investigate the effects of field salinity on seed yield, yield components, and leaf ionic concentrations in different safflower genotypes. A 2-yr field experiment was conducted in normal (E1) and saline (E2) field conditions using 64 safflower genotypes. Plant height, number of capitula per plant, number of seeds per capitulum, 1000-seed weight, seed yield, biological yield, and harvest index were determined in this study. Leaf concentrations of Na+ and K+ were also measured and the K+/Na+ ratio calculated. Results indicated that under salinity all the traits significantly decreased except tissue Na+ content and harvest index. Linear regression and genotype-by-traits analyses revealed a strong inverse association between leaf Na+ concentration and salinity tolerance. Results of stepwise multiple regression analysis showed that plant height, number of capitula per plant, biological yield, harvest index, and leaf Na+ content were the strongest predictors of seed yield, collectively explaining 97% of the variation in seed yield under saline conditions. Therefore, the only ionic predictor of salinity tolerance in the regression model, leaf Na+ concentration, can be suggested as an effective indirect screening criterion for salinity tolerance in safflower. The mechanisms of Na+ homoeostasis, including Na+-specific transport or K+/Na+ co-transport, could also be explored using the most contrasting genotypes with respect to salinity stress.