Effects of Foliar Application of Salicylic Acid on Growth and Physiological Attributes of Cowpea under Water Stress Conditions

The possible alleviating effects of salicylic acid on protection of cowpea (Vigna unguiculata) cv. Parastu under water stress conditions were investigated in the University of Zanjan Agriculture Research Station during 2008. Water stress was imposed by withholding irrigation at 50% flowering (flowering water stress, FWS) and when 50% of the pods grew 2-3cm (pod-formation water stress, PFWS). Salicylic acid (SA) was sprayed when plants had approximately ten fully expanded leaves with different concentrations of 0, 150, 300, 450 and 600 μM. Water stress was found to affect net photosynthesis rate, relative water content and Chlorophyll index. Proline content and leaf temperature increased in response to water stress. In both water stress treatments, plants treated with 300μM SA showed the highest values for net photosynthesis rate, transpiration rate and proline concentration. In FWS, the lowest leaf temperature was recorded in the control plants. However, in PFWS, leaf temperature was not affected by SA treatment. In FWS condition, the application of 300 μM SA showed the highest leaf area. It seems that the application of SA in 300 μM concentration may improve plant functions in both normal and stress conditions.