083 FRUIT HYDRAULIC BUDGETS IN FRENCH PRUNE (PRUNUS DOMESTICA L. CV. FRENCH) AND THEIR EFFECTS ON FRUIT GROWTH AND CRACKING

Abstract

End cracking of French prune fruits occurs when previously water stressed trees are irrigated during early July. Fruit phloem, xylem and transpiration flows (P, X and T, respectively) were measured diurnally during 72 h periods in mid June, early July and mid July (before, during and after the crack-susceptible period). Midway through each 72 h period, the previously stressed trees were irrigated. In mid June, X was larger than P, whereas P was larger than X during early July. In mid July, P and X were similar. In early July, the period preceding irrigation was characterized by an ourflow of phloem sap during the day and phloem inflow during the night. After irrigation, larger phloem inflows were observed and no phloem outflow occurred. Fruit transpiration rates were highly correlated with VPD. They exhibited a gradual decrease during the season, reaching minimum values during early July, before increasing again. The sum of P and X was virtually identical for the three periods i.e. stronger P's compensated for weaker X's and vice versa. Our results suggest that properties intrinsic to the fruit play the primary role in modulating water and photosynthate movements between the tree and the fruit. The possible role of these properties on fruit growth and cracking will be examined.