Pg. 23-31 How can tree starch reserves help us to better understand our trees?

Like in all woody plants, carbohydrates are also important in the growth of litchi trees. Starch concentrations of main branches of Mauritius litchi trees were determined as part of an orchard management program to increase yield and fruit size. Starch content varied from year to year and within a year, reflecting alternate bearing and tree phenology. Vegetative growth in autumn, flower panicle development and rapid fruit growth resulted in a decrease of starch reserves, whereas rest phases, such as the period prior to flower panicle development and periods between vegetative flushing, caused starch reserves to increase again. Starch concentrations after harvest and during flower induction were found to be positively correlated with yield of the following season. The period between harvest and flower induction is a very important period where orchard management can influence starch concentrations and therefore help the trees to increase their capacity to flower.

Summary:

• Carbohydrate reserves, specifically starch concentrations in main branches, play a crucial role in litchi tree growth, yield, and fruit size.
• Starch levels fluctuate throughout the year, reflecting tree phenology and alternate bearing, with depletion during vegetative growth, flowering, and rapid fruit development, and accumulation during rest phases.
• Higher starch concentrations after harvest and during flower induction correlate positively with better yields in the subsequent season.
• The study was conducted on 18-year-old Mauritius litchi trees in Nelspruit over multiple years, showing consistent seasonal patterns of starch fluctuation linked to vegetative and reproductive growth stages.
• Years with high yields (on-years) show lower starch reserves after harvest, causing delayed post-harvest vegetative flushes and reduced flowering, while low yield years (off-years) have higher starch reserves, explaining alternate bearing cycles.
• Management practices such as timely nitrogen fertilization, pruning, irrigation, and use of growth regulators (like Ethapon) during two critical periods (harvest to February and March to flower panicle emergence) can improve starch reserves and reduce alternate bearing.
• Late autumn vegetative flushing should be controlled to prevent starch depletion and negative effects on flowering.
• The study suggests optimizing orchard management based on starch reserve dynamics can increase tree productivity and yield over time.
• These findings align with international research on carbohydrate dynamics in fruit trees and provide a basis for improved litchi orchard management in South Africa.