Morphological and Physiological Response of Helianthus annuus L. to Drought Stress and Correlation of Wax Contents for Drought Tolerance Traits

Sunflower is the fourth most important oil seed crop of the world. Drought is a major limiting factor severely influencing the production sunflower. Cuticular wax is the outermost defensive layer which protect the plants from abiotic stress. In present investigation, ten sunflower genotypes were grown in growth chambers along with their controls. At the age of thirty days, drought stress was applied to these genotypes for ten days to study the impact of dehydration stress on different drought tolerance traits. Further, we studied the association of epicuticular wax load on drought-related traits, i.e., morpho-physiological traits, photosynthetic pigments, osmolyte contents and enzymatic activities both under stress and normal conditions. It was observed that sunflower genotypes subjected to drought stress enhanced wax load compared to normal plants. However, drought stress reduced leaf area, relative water contents, leaf water potential, osmotic adjustment and chlorophyll contents. In addition, proline, glycine betaine contents and antioxidant enzymatic activities of SOD, POD and CAT increased when plants were subjected to drought condition. Regression analysis indicated that osmolytes and antioxidant enzymatic activities showed positive correlation with wax quantity, whereas physiological traits showed negative correlation with wax load indicating elevation in wax quantity, reduced transpiration rate, leaf water potential and residual transpiration under drought condition. Based on findings, it can be concluded role of wax quantity can be exploited to develop genotypes with enhanced wax content to tolerate the drought stress and identification of drought resistant sunflower genotypes.