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

Five-year old 'Hosui' Asian pear (Pyrus serotina Rehder) trees growing in drainage lysimeters and trained onto a Tatura trellis were subject ed to three different irrigation regimes. Weekly water use (WU) was ca lculated using the mass-balance approach. Soil-water content of contro l lysimeters was kept at pot capacity, while deficit irrigation was ap plied before [regulated deficit irrigation (RDI)] and during the perio d of rapid fruit growth [late deficit irrigation (LDI)]. Soil-water co ntent was maintained at almost-equal-to 50 % and 75 % of pot capacity for RDI and LDI, respectively. Deficit irrigation reduced mean WU duri ng RDI and LDI by 20%. The reduced WU was caused by lower stomatal con ductance (g(s)) on deficit-irrigated trees. RDI trees had more-negativ e diurnal leaf water potentials (psi(l)). The psi(l), g(s), and WU rem ained lower for 2 weeks after RDI was discontinued. RDI reduced shoot extension and summer pruning weights, whereas winter pruning weights w ere not different between treatments. Except for the final week of RDI , fruit growth was not reduced, and fruit from RDI grew faster than th e control during the first week after RDI. In contrast, fruit volume m easurements showed that fruit growth was clearly inhibited by LDI. Fin al fruit size and yield, however, were not different between treatment s. Return bloom was reduced by RDI but was not affected by LDI.