Pg. 16-23 Effect of fungicides and disinfectants in the prevention of litchi pericarp browning and control of postharvest diseases

Pericarp browning, desiccation and decay are the most important postharvest problems affecting litchi fruit exported from South Africa. The standard approach for preserving the quality of litchi fruit involves the use of sulphur dioxide SO₂-fumigation. This study compared the efficacy of 18 disinfectants and 9 fungicides with SO₂-fumication and an untreated control in preserving the marketability of stored litchi fruit. All nine fungicides and 18 of the disinfectants improved, to various degrees, the marketability of litchi fruit compared to the untreated control. The disinfectant, OA5 DP, and fungicide, prochloraz, demonstrated superior efficacy to SO₂-fumigation in preserving overall fruit marketability, whereas the disinfectant Frigate^®, and fungicide benomyl, were equally effective as SO₂-fumigation. Five quaternary ammonium containing disinfectants, OA5 DP, Terminator^®, Formula 10^®. Sporekill^®, and Desogerm® two chlorine-based products. Harvest Wash^®, and HTH^®, and the fatty amine ethoxylate, Frigate^® reduced the incidence of fruit infection, comparable with SO₂ fumigation. Similar results were obtained from benomyl, copper oxychloride, guazatine, iprodione and prochloraz.

Summary:

• The study addresses the major postharvest problems in litchi fruit exported from South Africa: pericarp browning, desiccation, and decay.
• The standard preservation method is sulfur dioxide (SO₂) fumigation, but this has drawbacks including bleaching effects, aftertaste, ineffectiveness against some fungi, worker health risks, and EU residue limits.
• The study compared 18 disinfectants and 9 fungicides against SO₂ fumigation and an untreated control for their ability to preserve litchi fruit marketability during storage.
• All fungicides and most disinfectants improved fruit marketability compared to untreated controls.
• The disinfectant OAS DP and fungicide prochloraz showed superior efficacy to SO₂ fumigation, while disinfectant Frilate and fungicide benomyl were equally effective as SO₂ fumigation.
• Five quaternary ammonium disinfectants, chlorine-based products, and a fatty amine ethoxylate significantly reduced fruit infection incidence comparable to SO₂.
• Some fungicides like kresoxim-methyl eradicated Phomopsis sp., a common pathogen, and delayed pericarp browning and desiccation.
• High concentrations of certain fungicides (copper oxychloride, iprodione, kresoxim-methyl, thiabendazole) accelerated browning and desiccation, indicating concentration-dependent effects.
• Disinfectants generally improved marketability but their efficacy depends on concentration; higher concentrations sometimes caused bleaching or accelerated browning.
• The study emphasizes the potential of disinfectants as alternatives to SO₂ fumigation if used at appropriate concentrations, balancing efficacy with environmental and safety considerations.
• The effectiveness of treatments varied by cultivar and storage conditions, and extended storage at ambient temperature increased pericarp browning and fungal growth.
• The results support developing alternatives to SO₂ fumigation to reduce health risks and comply with residue limits while maintaining litchi quality during export storage.