EFFECT OF WATER AVAILABILITY ON THE PEDONCULAR FLOW AND THE GROWTH OF PEACH-TREES

The aim of this study was to determine the flows that account for fruit growth in the peach tree (Prunus persica (L) Batsch, cv Dixired) under different conditions of water availability. Young peach trees were grown in pots and were either watered continuously (control plants) or irrigated with reduced amounts of water (stressed plants). Variations in trunk diameter were recorded using LVDT (linear variable differential transformer) gauges and were used as an index of the water stress level. On each treatment the diameter variations were also recorded on some of the fruits with the same gauges. The fruits without continuous recording were measured with a digital caliper. The transpiration rate was found by regular weighing of picked fruits or by recording diameter variations using LVDT gauges. The average weight increase on stressed fruits was 62% of the control. Massic pedoncular flow was defined as the fresh weight increase plus the transpiration. Respiration losses were quantitatively negligible. During the period under study, the peach transpiration was about 70% of the pedoncular flow. When the tree was not stressed, the pedoncular flow, which was computed hourly, was positively linked to the climatic demand for water. It was minimum in the early morning and maximum in the mid-afternoon. The daily pedoncular flow increased from less than 1 g to about 30 g during the last month before maturity. The pedoncular flow in the stressed tree was negatively linked to the climatic demand for water during the photoperiod. The cumulated massic pedoncular flow of a stressed peach was 66% of the control. Compared with the control, there was a highly significant linear relationship between the decrease of the massic pedoncular flow of the water-stressed peach and the increase in the maximum daily shrinkage of its trunk.