Apricot water relation and fruit growth under progressive water stress conditions

Apricot (Prunus armeniaca L.) is among the most cultivated fruit worldwide, appreciated for its taste and appearance. Previous studies on the application of regulated deficit irrigation (RDI) strategies have demonstrated how this species can successfully respond to water stress, also increasing some qualitative traits. This work aims to investigate the physiological response of plants in absence of irrigation water during the last weeks before harvest. A total of 12 plants were considered in this study, 6 subjected to water stress and 6 control, divided in two blocks per treatment. In the “stress” treatment the irrigation was withheld on June 28 (108 days after full bloom, DAFB) and remained so until harvest, at 131 DAFB, while control trees were irrigated according to ETc. Stem and leaf water potentials as well as leaf gas exchange were measured at 108 and at 131 DAFB and fruit vascular flows data were registered every 15 min at 115 and 128 DAFB. Leaf water potential did not show differences between the two treatments, while stem water potential reached statistically significant lower values at harvest (131 DAFB). In the plants subjected to water stress, the photosynthetic rate was not affected, while transpiration and stomatal conductance presented statistically significant lower values at harvest. Control plants were able to transpire more, with higher xylem and phloem inflow. However, fruit quality traits were similar in the two treatments, with the only difference in the chlorophyll degradation level, meaning that stress conditions slightly delayed fruit ripening. These results lead to the conclusion that apricot can afford important water shortages without negative impacts on productivity, while increasing its water use efficiency.