From the Archives of the Rare Fruit Council of Australia, inc.
by A. J. Joubert, Citrus and Subtropical Fruit Research Institute, Nelspruit, South Africa

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Fruit Crack in Lychees

Litchi chinensis

One of the most common problems in litchi production is the large percentage of fruit that crack during the ripening process. The causes of fruit crack cannot be attributed to a single factor, and the phenomenon can differ from orchard to orchard or from one region to the next. Fruit crack occurs during the third stage of fruit development. This is after cell division has ceased in the pericarp (skin) and cell stretching takes place.

It has been established that cell division in the skin ceases about 70 days after fertilisation. From this stage until the end of the fruit growth period, i. e. after another 35 days (Stage III), cell stretching takes place in the skin. During this period, the edible portion (aril) that grows between the seed and the skin, enlarges very rapidly, causing tremendous inner tension against the skin which then has to stretch very quickly.

Skin strength, i. e. resistance to cracking, is determined by the number of cells formed during the first 10 weeks of fruit development. Since the litchi skin has this weak characteristic, it is essential that optimum conditions for cell division be created during fruit growth Stages I and II. Any lack, for example, of water or nutrients at this stage, will hamper cell division and too few cells will be formed. The tension in the cells during Stage III will then be very high, resulting in skin crack. It is notable that the skin cracks after long, wet spells when much water is taken up. The skin cracks according to an easily identifiable pattern across the length (tip) of the fruit.

A second cause of fruit crack is skin damage during Stage III when only cell stretch takes place. Damaged cells cannot recover during this period and since the cells are dead at that time, they will also not be able to stretch and the skin will tear as the tension (pressure) of the enlarging aril increases inside the skin. This tension causes the skin to crack at damaged or weak spots. The most common factors that play a role in this regard are insect, hail and sunburn damage when relative humidity is low.

Browning is a symptom of cell necrosis which starts in the internal cell layers (mesocarp) of the skin once cell division has stopped and the cell begin to stretch. In an advanced stage, the browned cells die and dry out. It has been established that browning is not caused by insect damage or fungal diseases. However, as yet, the primary cause of browning has not been established, but the following factors could be directly involved:

Early ageing and dying of the cells due to an imbalance in nutrients.
The tremendous cell tension in the pericarp that could cause cell damage.
High temperatures together with low humidity during the fruit growth period.
Secretion of volatile, harmful substances by the actively-developing aril that could adversely affect the ageing pericarp cells.

To summarise, browning is a condition of early cell deterioration and necrosis. To prevent fruit crack, it is recommended that litchis be grown in such a way that all the deleterious factors can be restricted or eliminated.

(Reprinted from Farming in South Africa 1983). Extract from Sunshine Coast Sub Tropical Fruits Association Newsletter May, 1986.

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Joubert, A. J. "Fruit Crack in Lychees." Archives of the Rare Fruit Council of Australia.Citrus and Subtropical Fruit Research Institute, Nelspruit, South Africa. May. 1986. Web. 28 Mar. 2015.

Published 28 Mar. 2015 LR
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