Studies on shoot, flower and fruit development in litchi and strategies for improved litchi production.

摘要

This paper reviews management practices at important litchi developmental phases for sustainable production. These phases include: postharvest flush growth, an important phase for fostering high quality bearing shoots for the next season; the transition from vegetative growth to reproductive growth, a phase to control growth of new vegetative flush; panicle growth, a phase that determines flower quality; blooming, a phase for pollination and fertilization; and finally fruit development with yield and quality formation. High quality shoots are the basis for productivity. A "high quality" shoot includes three interrelated characters. Firstly, it is strong with plenty of healthy leaves. Secondly, it has a build-up of carbohydrate reserve. Thirdly and most importantly, it matures at the right time, which is crucial for flower induction. The time window for flower induction is a function of flush maturity and chilling period. Prevention of immature flush in winter is the key to obtain reliable flowering. Various methods of controlling flush cycle, including girdling, water withholding, growth retardants and flush killers have been applied to promote flowering. Yet, a clear understanding of the regulatory mechanisms of flush cycle is still in need. Carbohydrate reserves in shoots serve as an important resource for flowering and fruit set. Flowering in cultivars like 'Feizixiao' bearing large panicles is nutritionally costly and depletes carbohydrate reserve in shoots, resulting in poor fruit set. Reducing panicle size by panicle pruning in these cultivars improves pollen or embryo sac viability and promotes fruit set. High initial fruit set is crucial for productivity as it suppresses competing summer flush, which can lead to massive fruit drop. Effective pollination is the key for initial set, and introducing honey bee colonies to orchard is very helpful. Diseases and pests induce excessive fruit drop and should be well controlled during fruit growth. Auxin-like chemicals are applied especially in stress conditions to improve fruit retention. Sufficient irrigation and supply of minerals during fruit growth are fundamental to large fruit size. Colouration of litchi can be promoted by bagging. The treatment also protects fruit from damage of pests and saves sprays of pesticides.