The relationship between fruit and leaf growth in lychee (Litchi chinensis Sonn.)

The relationship between fruit and leaf growth was investigated in lychee (Litchi chinensis Sonn.) in a series of experiments in subtropical Australia (lat. 27degreesS). Particles were removed at flowering to encourage new leaf growth on half the branches of each tree during fruit development. Some of the trees were pruned every week to prevent all vegetative growth, to test the effect of flower removal alone without subsequent leaf growth. In other experiments, the effect of pruning 50% of the branches was studied, but the pruning was scattered across the tree, rather than on one side. The yields of pruned trees with or without leaf flushes were more than 50% of the yield of the control plots in ten out of eleven cases, indicating that new leaves on one branch did not usually compete with fruit on adjacent branches. Concentrations of starch declined from flowering to harvest, and were higher in the branches than in the leaves, twigs, trunk and roots. In contrast, the effects of pruning were generally small. Concentrations of starch in the branches were sometimes higher when leaf or fruit growth was suppressed after pruning compared with branches with new growth. There were also slightly higher concentrations of starch in branches with leafy shoots than in those carrying fruit. These results suggest that the new leaves and fruit are more dependent on current assimilation than on stored reserves. New leaves on one branch do not reduce fruit growth in adjacent branches.