- J H Lonsdale
- Department of Microbiology and Plant Pathology, University of Pertoria, Pretoria 0002
- 1988
South Africa produces less than 5000 tons of litchis per annum of which less than half is exported (Swarts, 1985). One of the main reasons for this, is the rapid loss of marketability of litchis after harvest. The litchi skin soon dries out after harvest and becomes brown and brittle. The fruit is also susceptible to postharvest decay caused by a variety of micro-organisms. Roth (1963) examined the micro-organisms involved in the decay of litchi fruit and found that bacteria, yeasts and several other fungi were present in the proportion 3:96:1.
Due to high air tariffs, most of the South African litchis are exported to overseas markets by ship. As a result of this, fruit is stored for up to 30 days before reaching the consumer (Swarts and Anderson, 1980). For a postharvest treatment to be effective, it must therefore protect the fruit from decay for up to 30 days.
Summary:
- South Africa produces less than 5,000 tons of litchis annually, with less than half exported, largely due to rapid postharvest loss of marketability caused by skin drying and fungal decay.
- Postharvest decay in litchis is mainly caused by fungi, with nine primary fungal pathogens identified including Aspergillus species, Botryodiplodia theobromae, Colletotrichum gloeosporioides, Cylindrocarpon tonkinense, and Pestalotia species.
- Bacteria and yeasts also contribute to decay, but fungi are the main culprits; infection often enters through tiny lesions caused by fruit fly stings.
- Symptoms of fungal infections include lesions, discoloration, cottony mycelium growth, and fruit rot that often starts at the stalk end or as circular patches.
- Effective postharvest disease control depends on timing; diseases from field infections are harder to control postharvest than those arising during or after harvest.
- Physical control includes low temperature storage which slows fungal growth but can cause chilling injury if below 7°C for too long; refrigeration reduces decay but does not prevent browning.
- Packaging in polyethylene bags helps reduce browning, rotting, and weight loss.
- Gamma irradiation has shown promise but is not widely studied for litchis.
- Chemical treatments involve dips in fungicides such as benomyl, dicloran, prochloraz, and sodium-o-phenyl phenate (SOPP), with hot treatments (52°C) more effective than cold.
- Fungicide mixtures tend to provide better disease control than single fungicides.
- Some antibiotics and nickel salts also show potential for controlling specific fungal pathogens.
- Postharvest control strategies are not yet fully registered for commercial use in South Africa.
Indirect control of fruit flies, which create infection entry points, may help reduce decay.