Response of Water-stressed Young Peach Trees to Foliar Applications of Ascorbic Acid

Limited water availability is a concern for fruit tree growers and nurseries in many regions in many part of the world In recent years, the exogenous (foliarly spray) application of biochemicals or natural chemicals has been proved to increase water stress tolerance in several crops. The effect of exogenous foliar applications of ascorbic acid (AA) on gas exchange, water relations, and chlorophyll fluorescence was assessed in one-year-old peach trees in order to confer resistance to water stress. Trees were grown under two water conditions: water-stressed trees and well-watered trees (control; watered to field capacity every three days). Two cultivars, Scarletprince and Carotiger, grafted onto Guardian^TM rootstock were used. Ascorbic acid at 250 ppm concentration was tested. Five treatments were applied: 1) control without AA spray application (untreated control); 2) control with AA; 3) water-stressed trees without spray application; 4) water-stressed trees treated with AA only once (this application was done when soil volumetric water content in the pots of water-stressed trees fell below 50% of the values observed in the control trees); and 5) water-stress trees treated with AA twice (trees received the same application as treatment four plus another application one week later). All trees were watered to field capacity two weeks after the first application. Responses after AA application were different in each cultivar. Ascorbic acid increased CO₂ assimilation and stomatal conductance in water-stressed 'Scarletprince' trees that received only one spray application. A second application did not improve gas exchange parameters in 'Scarletprince' trees. Nevertheless, all sprayed 'Scarletprince' trees had CO₂ assimilation and stomatal conductance similar to control trees upon rewatering, but water-stressed trees that had not received AA did not recover photosynthetical functions. Also, stem water potential in AA-sprayed water-stressed 'Scarletprince' trees was similar to control trees whereas non-sprayed water-stressed trees had significantly lower values than control trees. On the other hand, gas exchange parameters were not affected by the AA treatments in 'Carotiger' during the water stress period but their performance after rewatering was better than the trees that were not AA sprayed. Neither water stress nor the ascorbic acid treatments affected the efficiency of photosynthetic apparatus based on chlorophyll fluorescence measurements in any of the cultivars. In summary, these initial results indicate that exogenous applications of AA could be used as a friendly environmental management tool for trees to cope with suboptimal water conditions.