WATER-USE, GROWTH, AND FRUIT YIELD OF HOSUI ASIAN PEARS UNDER DEFICIT IRRIGATION

Five-year old 'Hosui' Asian pear (Pyrus serotina Rehder) trees growing in drainage lysimeters and trained onto a Tatura trellis were subjected to three different irrigation regimes. Weekly water use (WU) was calculated using the mass-balance approach. Soil-water content of control lysimeters was kept at pot capacity, while deficit irrigation was applied before [regulated deficit irrigation (RDI)] and during the period of rapid fruit growth [late deficit irrigation (LDI)]. Soil-water content was maintained at almost-equal-to 50 % and 75 % of pot capacity for RDI and LDI, respectively. Deficit irrigation reduced mean WU during RDI and LDI by 20%. The reduced WU was caused by lower stomatal conductance (g(s)) on deficit-irrigated trees. RDI trees had more-negative diurnal leaf water potentials (psi(l)). The psi(l), g(s), and WU remained lower for 2 weeks after RDI was discontinued. RDI reduced shoot extension and summer pruning weights, whereas winter pruning weights were not different between treatments. Except for the final week of RDI, fruit growth was not reduced, and fruit from RDI grew faster than the control during the first week after RDI. In contrast, fruit volume measurements showed that fruit growth was clearly inhibited by LDI. Final fruit size and yield, however, were not different between treatments. Return bloom was reduced by RDI but was not affected by LDI.