Low water stress conditions in table olive trees (Olea europaea L.) during pit hardening produced a different response of fruit and leaf water relations

The scarcity of water for agricultural use is producing a generalization of deficit irrigations in most of the fruit trees. Regulated deficit irrigation in olive trees is scheduled with a period of water stress during the pit hardening phase with low or, even, no decrease in yield. During this phenological stage, fruit is a great sink of assimilates and competes with vegetative growth, producing a significant change in the water relation of the tree. The aim of this work is to study the water relations in leaves and fruits in a period of drought during the phenological stage of pit hardening in a mature (43-year-old) table olive orchard. Water relations of leaves and fruits were compared between a Control of fully irrigated trees and Stressed trees (with a period of drought from 1 week after the beginning of pit hardening until 1 week before harvest). The water stress conditions were considered as low level, according with the stem water potential data. Leaf water relations were quickly affected with a reduction of midday stem water potential and turgor pressure at 14 days after the beginning of the drought (DABD). Leaf osmotic adjustment was measured only at the end of the drought cycle (63DABD). On the other hand, fruit water relations were affected slowly and only osmotic potential was reduced at 14DABD. Such variations produced a change in the source of water flow from xylem to phloem according to the variations in leaf–fruit water potential. The pattern of adaptation of leaves and fruit during the drought cycle and the relationship between them is discussed.