Exogenous ABA Treatment Facilitates Date Fruit Ripening

The date palm (Phoenix dactylifera L.) is a subtropical monocot tree(Nixon, 1951). Date fruit development and ripening requires very high temperature and low relative humidity (Lobo et al., 2013). In habitats where these terms are inadequately supplied, delay in fruit ripening results in deterioration of large yield portions. The main objective of the current study is to uncover mechanisms regulating date fruit ripening. Based on the role of the plant hormone abscisic acid (ABA) in the regulation of non-climacteric fruit ripening, we hypothesized that ABA might play a role in the regulation of date fruit ripening. Monitoring ABA levels along the course of fruit development reveals a constant increase in endogenous ABA levels at the fruit-pericarp, starting from 16 weeks post-pollination (WPP), as fruit colour changes from green-to-yellow. Exogenous ABA application to the developing fruit 16 WPP enhanced chlorophyll degradation, facilitating the transition from green-to-yellow, compared to control fruits. In addition, the ABA treatment facilitated sugar accumulation, as indicated by an earlier increase in the pericarp Brix value, compared to control fruit. Interestingly, post-harvest ABA treatment facilitated the ripening of mature date fruit, as indicated by a significantly faster occurrence of peel browning and fruit flesh softening, compared to control fruits. These results suggest that ABA plays a pivotal role in the regulation of date fruit ripening. Fine-tuning of ABA applications may provide practical tools to control date fruit maturation and ripening under sub-optimal conditions, thus reducing yield losses and harvesting costs, and improving fruit quality.