Effects of Foliar Application of Salicylic Acid on Improvement of Drought Tolerance in Madagascar Periwinkle

This study was conducted to evaluate the effects of exogenous applications of salicylic acid on improvement of drought tolerance in Madagascar periwinkle (Catharanthus roseus L.). The experiment was arranged as factorial based on a completely randomized design (CRD). Salicylic acid concentrations of 0, 0.5, 1, 1.5 mM were foliar sprayed on pot plants treated with three levels of irrigation including 30%, 60%, and 100% Field Capacity). Application of salicylic acid was repeated three times with three-day interval, while plants were exposed to drought stress for four weeks. The traits such as flower number, flower diameter, fresh weigh of individual flower, shoot number, and water use efficiency (WUE) were evaluated in this study. Based on the results, the effect of salicylic acid on severe deficit irrigation (30% PC) was significant, and the highest number of flowers at this level was observed in foliar application of 0.5 and 1 mM salicylic acid. Also, the highest fresh weight of single flower and number of sub-branches were obtained in application of 0.5 mM salicylic acid under severe deficit irrigation. In addition, exogenous salicylic acid at all levels significantly improved the flower diameter, which could have a major impact on the aesthetic properties of this plant under deficit-irrigation conditions. In total, due to availability of salicylic acid and easy use, foliar application of salicylic acid at 0.5 mM concentration would be recommended to improve Madagascar periwinkle drought tolerance under severe deficit irrigation.