Pg. 41-43 The importance of Carbohydrate Reserves on Lychee Production

Carbohydrates have been considered to be important in the productivity of lychee (litchi), and are a useful index of potential yield. However, it is not known which plant parts reflect the reserves that are 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 Queensland, Australia (lat 27°S) were uprooted and dissected into nine parts just after panicle emergence in July and August for determination of starch concentration. 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 from 1 to 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 only accounted for 35% of the tree’s dry weight. In contrast, the 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.

The greatest seasonal fluctuations in starch concentration occurred in the small branches with a two to ten 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 twig (two to nine fold difference), medium branches (one to three fold difference) and large branches (one to two fold difference). In contrast, starch in the leaves, trunk and major roots was relatively stable.

Small and medium branches from 1 to 5 cm in diameter should be used for sampling the carbohydrate status of lychee, since they contained about half of the tree’s starch and also indicated the reserves that were used for new leaf and fruit growth, and potential yield.

Summary:

• Carbohydrates, especially starch reserves, are crucial for the productivity of lychee trees and serve as a useful index for potential yield.
• The study examined starch concentration and total reserves in different parts of six-year-old lychee trees from various cultivars grown in subtropical Queensland, Australia.
• About half of the tree’s starch reserves were found in small and medium branches (1 to 5 cm diameter), despite these branches comprising only 35% of the tree’s dry weight. This is due to their high starch concentration (8.1 to 9.6%).
• Leaves accounted for about a quarter of the tree’s biomass but contributed only about 8% of starch reserves due to their low starch concentration (~2.2%).
• The trunk and roots contained about a sixth of starch reserves with starch concentrations between 2.8 to 7.2%, making up about a fifth of the tree’s dry weight.
• Seasonal changes in starch concentration were most pronounced in small branches, fluctuating two to tenfold depending on vegetative growth and fruiting stages.
• Starch declined during or just after vegetative growth (February to June), peaked before flowering (September), and declined during fruit development towards harvest (December-January).
• Similar but less pronounced fluctuations were seen in twigs, medium and large branches, while leaves, trunk, and major roots showed relatively stable starch levels.
• The small and medium branches are the best plant parts to sample for assessing carbohydrate status and potential yield.
• The starch reserves in branches are likely the source for new leaf and fruit growth, indicating their importance in lychee production and yield potential.
• The study suggests that carbohydrate reserves near growing shoots better reflect the tree’s status than starch in trunk or roots.
• These findings help inform management practices for optimizing lychee yield through understanding and monitoring carbohydrate reserves.