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Drip-irrigated Bulida apricot trees (Prunus armeniaca L.) on Real Fino apricot rootstock were submitted, for 4 consecutive years, to water stress by withholding irrigation at different phenological periods: during the period of flowering-fruit set which lasted around 1 month (T-1 treatment); during stages I + II of fruit growth (including the initial exponential phase and the lag phase of the double-sigmoid curve), which lasted around 2 months (T-2 treatment); during stage III of fruit growth (second exponential phase) lasting around 1 month (T-3 treatment); immediately after harvest for one and a half months (T-4 treatment); and for 2 months during late postharvest, immediately following the T-4 treatment (T-5 treatment). These stress treatments were compared with a control treatment (T-0), irrigated throughout the year and receiving an amount of water equivalent to 100% of the crop evapotranspiration (ETc) demand. The greatest reduction in volumetric soil water content, leaf water potential and leaf conductance with respect to the control values was observed in plants from T-4 and T-5 treatments. A clear distinction could be made between the main periods of shoot and fruit growth in apricot trees, which may be considered an advantageous characteristic for the application of deficit irrigation. Trunk circumference growth and canopy shaded area were unaffected by irrigation treatments. Stressed fruits from the T-2 treatment had a lower diameter during the water stress period, although they showed a compensatory growth rate after irrigation, reaching a similar size to fruits from the control treatment at harvest. Two critical periods for withholding irrigation were found. The first corresponded to the second rapid fruit growth period (T-3 treatment), in which the water stress induced a reduction in yield due to a smaller fruit size at harvest. In addition, fruits from this treatment ripened earlier. The second critical period was immediately postharvest (T-4 treatment), in which water stress induced a significant decrease in fruit yield the following year, due to an increase in young fruit drop which lead to a lower final fruit set. |
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