Litchi fruit abscission: its patterns, effect of shading and relation to endogenous abscisic acid

Abstract

In litchi (lychee), three waves of fruit drop were generally designated when the intensity of abscission was expressed as a relative rate. An additional wave of pre-harvest drop was detected in cultivars with aborted seeds. Fruit drop accentuated by shading treatment indicates that reduced incident solar radiation by overcast weather in the post-bloom period could be a major hindrance to the set. High leaves-to-panicle ratio was found to be needed for a normal set. Shading reduced photosynthesis but also enhanced the abscisic acid levels in the fruits. The abscisic acid levels were positively correlated with abscission, regardless of whether it was caused by non-pollination or by shading. Seed abscisic acid peaks were concomitant with the waves of fruit-drop. It is suggested that abscisic acid promotes litchi fruit abscission antagonistically to the role of auxin.