Carbohydrate reserves in lychee trees (Litehi chinensisSonn.)

Abstract

Carbohydrates have been considered important in the productivity of lychee (Litchi chinensis Sonn.), but it is not known which plant parts best reflect the reserves available for new growth. Six year old lychee trees (cvs Tai So, Bengal, Brewster, Souey Tung, Haak Yip, Kwai May Pink, Salathiel and Wai Chee) growing in subtropical Australia (lat. 27°S) were uprooted and dissected into nine parts just after panicle emergence in July and August for determination of starch concentration. The pools of starch in a flowering and a vegetative tree (eight year old Kwai May Pink lychee), the effect of cincturing on starch reserves of cv. Bengal, and seasonal changes in starch concentration in four orchards (cvs Tai So at two sites, Bengal and Kwai May Pink) over a single year were also examined. In the destructive harvests of the lychee cultivars, about half of the tree’s starch reserves were found in the small and medium branches 1-5 cm in diameter. This was due to their high concentration of starch (8.1 to 9.6% compared with 2.2 to 7.8% in the other plant parts) since they accounted for only 35% of the tree’s dry weight. In contrast, leaves accounted for about a quarter of the tree’s biomass, but contributed only about 8% of the starch reserves because the starch concentration was only 2.2%. The trunk and the roots contained about a sixth of the tree’s starch reserves, with starch concentrations of 2.8 to 7.2%, but only a fifth of the tree’s dry weight. Starch concentrations were higher in all parts of a flowering tree with floral buds just visible than in a vegetative tree with early to mid-flush development. Cincturing after the maturation of the post-harvest vegetative flush in April increased starch concentrations in tissues above the cut and decreased it below the cincture. The greatest seasonal fluctuations in starch concentration occurred in small branches with a 2-10 fold difference, depending on the amount of vegetative growth and fruiting. Starch generally declined during or just after vegetative growth from February to June, reached a maximum in September before anthesis, and then declined during fruit development with harvests in December or January. Similar, but less dramatic changes occurred in the twigs (2-9 fold difference), medium branches (1-3 fold difference) and large branches (1-2 fold difference). In contrast, starch in the leaves, trunk and major roots was relatively stable. Small and medium branches 1-5 cm in diameter should be used for sampling the carbohydrate status of lychee, since they contain about half of the tree’s starch and also indicated the reserves used for new leaf and fruit growth.