Influence of Water Stress in Autumn on Flower Induction and Fruiting in Young Pomelo Trees (Citrus grandis (L.) Osbeck).

Abstract

Young pomelo trees grown in concrete pots in a plastic house were water-stressed for different durations from early September to late December, 1990. The cyclical stress treatments were established by withholding water from the potted trees until the leaf water potentials reached-24 to-28 bars (7 to 13 days after irrigation) at which time they were re-irrigated. Maximum day and minimum night temperatures in the plastic house were adjusted to about 25° and 10°C, respectively, from early December, 1990, to early April of the following year. 1. Trees, subjected to water stress from early September hardly grew in the fall, whereas those stressed from early October and the control trees sent forth several shoots per tree. The number and length of the spring shoots which sprouted in the following year were not significantly different among the treatments. 2. The number of inflorescences, flower buds, and flowers which opened, increased as the duration of water stress was extended. Anthesis was advanced in trees from which fall shoots failed to sprout but not in trees that produced fall shoots. The stress treatments had no effect on the % fruit set which ranged from 0.1 to 1.1 for leafless flowers and 4.8 to 6.0 for leafly ones. 3. Comparison of analyses made in late December between leaves of stressed trees with and without fall shoots revealed that leaf sugar content increased while starch content decreased, the magnitude of the difference being proportional to the duration of the stress period. Leaf N content was significantly higher in stressed trees compared to unstressed ones. No significant difference in C : N ratio in leaves was observed in late December among the treatments.