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 indicates that leaf area growth was limited during the summer due to competition 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 interaction between plant fruit load and VPD: the higher the leaf: fruit ratio the greater the responses to a reduction in VPD (increase in fruit DM, fruit diameter, fruit and leaf expansion rate). The data suggest that under high fruit loads, water and carbohydrates limit growth under Mediterranean summer conditions. 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 availability of water and carbohydrates. (C) 2001 Annals of Botany Company.