The mechanism of enhancing drought tolerance threshold of pepper plant treated with putrescine and salicylic acid

Pepper is a warm-season crop and water deficit is considered as dominant issue in pepper cultivation. Using plant growth regulators in different steps of plant growth and development could be as useful strategy to overcome adverse effects of abiotic stresses. In order to investigate the morpho-physiological responses of pepper plant to putrescine (Put) and salicylic acid (SA) foliar application and deficit irrigation (DI) strategy, the split plot experiments were laid out based on randomized complete blocks design at University of Zanjan. The highest values of leaf area and total yield were recorded in sprayed plants by Put at 1.5 mM under DI0% (5842 cm2 and 9.6 ton ha-1). SA at 1.5 mM was the best treatment to increase vitamin C content of pepper fruits. Free proline content increased by 41.34% in sprayed plants by Put at 1.5 mM (7.5 & mu;m g � 1 FW) compared to control. SA treatment increased number of pepper fruits, size of harvested fruits and total produced yield by regulation of stomatal conductance and increasing leaf chlorophyll content of pepper plants under drought stress conditions. Also, Put foliar treatment increased drought tolerance rate of pepper plant by increasing free proline content, peroxidase enzyme activity and water use efficiency and also applying this treatment could significantly reduce electrolyte leakage rate. So, SA and Put foliar application at 1.5 mM concentration could be recommended as widely used technique to overcome adverse effects of drought stress on pepper plants cultivated in arid and semi-arid regions.