POSTHARVEST WATER-STRESS OF AN EARLY-MATURING PLUM

Postharvest water stress was imposed on a May harvested plum (Prunus s alicina Lindl. cv. Red Beaut) over a three year period. Control trees were irrigated at approximately 100% ET. One stress treatment (T1) rec eived 50% of the water applied to the control. The second stress treat ment (T2) was subjected to cycles of on-and-off irrigation which varie d from year to year. AH treatments were fully irrigated at about 100% ET through harvest. Treatment T1 received about 30 cm less irrigation water than the control and showed no decrease in yield, fruit weight o r fruit quality over all three years. Treatment T2 received about the same amount: of water as T1 in the first two years of the experiment a nd also showed no decrease in productivity. in the third year, T2 was irrigated only for a single three week period after harvest which save d over 60 cm of applied water. The trees were extensively defoliated b y the end of the season, showed some shoot and scaffold dieback, and h ad reduced yields in the following year. Double fruit formation was lo w in all treatments and Was not increased by stress. Stem water potent ial (SWP) measurements followed a consistent seasonal pattern in the c ontrol. In the final year of the experiment, SWP during the postharves t period correlated well with yield in the following spring. This sugg ests SWP might be useful for monitoring stress, thus preventing a loss in productivity while saving some water.