Fruit cracking in litchi (Litchi chinensis): An overview

Abstract

Litchi (Litchi chinensis Sonn.), an arillate fruit species of China origin, possessed a unique structure comprising thin and leathery pericarp that enclosed the aril as its edible part. Fruit cracking is a serious physiological disorder in litchi that occurs during its growth and development, and causes significant loss of economic yield. Fruit cracking in litchi coincides with a period characterized by high day temperature (35-40°C) and low relative humidity (60%). It entails the implicated roles of both internal and external factors. Besides climatic effects, abnormal development of the skin during early fruit growth promotes the disorder. In this context, a concept, ball skin versus bladder effect was theorized to describe the relationship between a pre-grown skin and a growing aril. To further conceptualize the problem, Zig-zag Unfolding model was developed which decipher the role of spongy tissue in pericarp extensibility necessary for preventing pericarp cracking. Cracking occurs during the final stage of fruit growth when the aril develops and exerts pressure on the inactively growing pericarp. Thus, a balance between turgor pressure from the expanding aril and the mechanical structure and elasticity of skin is indispensable to prevent fruit cracking. Fruit cracking can be controlled by application of calcium nitrate (0.5 - 1%), borax (0.4 - 0.8%), Zn (0.4%), GA3 (10 ppm) alone or in combinations assured with timely irrigation, mulching, bagging of fruit bunches, use of shade nets and growing cracking resistant cultivars.