Modulation of competition between fruits and leaves by flower pruning and water fogging, and consequences on tomato leaf and fruit growth

The effects of water fogging and reducing plant fruit load were studied in a tomato crop grown in a glasshouse under Mediterranean summer conditions. The objective of these treatments was to reduce competition between leaves and fruits for carbohydrates and water. Flower pruning increased plant leaf area and increased fruit, stem, lamina and petiole dry mass (DM). This ind icates that leaf area growth was limited during the summer due to competiti on between fruits and leaves for assimilates. In contrast, reducing the air vapour pressure deficit (VPD) by water fogging had no effect on plant leaf area or aerial plant DM. Interestingly, there was a significant interactio n between plant fruit load and VPD: the higher the leaf: fruit ratio the gr eater the responses to a reduction in VPD (increase in fruit DM, fruit diam eter, fruit and leaf expansion rate). The data suggest that under high frui t loads, water and carbohydrates limit growth under Mediterranean summer co nditions. However, reducing VPD was not always sufficient to enhance fruit and leaf growth. This might be due to the lower leaf area under high fruit load. In contrast, reducing VPD under low fruit load triggered higher rates of leaf and fruit expansion; this is probably linked to a greater availabi lity of water and carbohydrates. (C) 2001 Annals of Botany Company.