Pg. 26-27 Pheno/Physiological Patterns of Litchi Trees

This paper is a report on phenological studies conducted with litchi trees and some associated physiological patterns related to the phenology.

In the phenology studies the cyclic occurrence of events of tree and fruit development such as bud development, flowering, vegetative flushes, fruit set, fruit development, root growth, etc., were recorded. The determination of the seasonal pattern of starch accumulation and utilization was combined with this study to establish physiological indicators within the litchi tree.

The litchi tree phenology differs substantially from many other subtropical tree crops in that leaf growth flushes always precede flowering and fruit development, thus eliminating much of the competition between leaf development and fruiting. The new leaves from the first flush are in fact able to contribute to the carbohydrate energy requirement of the flowering process, and later, the leaves of both flushes contribute to fruit development.

The most important physiological process of the litchi tree (and in fact in all plants) is that of photosynthesis which involves the harnessing of light energy for the initial production of sugars from carbon dioxide and water. This supplies the plant with a source of chemical energy and basic building units for the reactions that take place.

The litchi tree stores most of its carbohydrate reserves as starch in its thinner branches of 10 mm to 50 mm diameter (Menzel et al., 1995). This also differs from other tree crops, e.g. mango trees, where starch reserves are stored mainly in the roots, main stem and frame branches (Davie et al.,1995). The litchi tree appears to have a relatively small root structure. Studies by Menzel et al. (1995) on excavated litchi trees indicated that the ratio of root dry material to aerial dry matter is of the order of 1 :6 (i.e. 1 kg roots for every 6 kg of plant matter above ground level) while the ratio with mango trees is about 1 :3,5 (Davie et al., 1995).

Summary:

• The paper reports on phenological studies of litchi trees, focusing on cyclic events such as bud development, flowering, vegetative flushes, fruit set, fruit development, and root growth.
• The study combines phenology with analysis of seasonal starch accumulation and utilization in the tree’s branches to establish physiological indicators.
• Litchi tree phenology differs from many other subtropical fruit trees because leaf growth flushes always precede flowering and fruit development, reducing competition between leaf growth and fruiting.
• New leaves from the first flush support the carbohydrate energy demands of flowering, and leaves from both flushes contribute to fruit development.
• Photosynthesis is the key physiological process providing energy and building blocks for the tree’s activities.
• Litchi trees store most carbohydrate reserves as starch in thinner branches (10-50 mm diameter), unlike some other trees like mango that store starch mainly in roots and main stems.
• Litchi trees have relatively small root systems; the root dry mass is about one-sixth of the aerial dry matter.
• Phenology was regularly recorded over four years from different farms and climatic conditions to account for variability.
• The main cultivars studied were HLH Mauritius and Madras Red, with additional cultivars included where available.
• Phenological events showed shifts between years, locations, and cultivars, with climate playing a major role. Shifts in harvest dates could be up to four months depending on conditions.
• The phenology for HLH Mauritius shows: leaf flush peak April-June, full flowering in September, fruit set starts in August, rapid fruit development October to mid-November, and harvest in December. Root growth peaks between December and March.
• Starch levels in branches start very low after harvest, take two months to recover coinciding with root growth and leaf flushes, peak before flowering, dip sharply during high energy-demand flowering, recover post-flowering to a maximum just before high demand from developing fruit depletes reserves again.
• The Madras cultivar shows a higher peak starch concentration earlier but fails to recover starch reserves as much as HLH Mauritius, which may contribute to its later fruit maturation.
• The phenology combined with starch patterns can guide management practices like timing fertilization, girdling, and water stress application.
• Recommendations include creating detailed farm-specific phenology charts, cautious management of nitrogen fertilization and water stress timing so as not to impair starch reserve recovery, and studying mineral nutrient uptake timing for optimal tree physiology.