Pg. 36-40 Biological Control of Litchi Fruit Diseases

Microbial epiphytes isolated from chemically sprayed and unsprayed litchi trees, yielded three promising antagonists, later identified as Bacillus stearotermophilus, Bacillus megaterium and Bacillus licheniformis. These isolates effectively inhibited Phomopsis sp, Pestalotia sp, Alternaria alternata, Penicillium sp. and seven unidentified litchi post-harvest pathogens, when evaluated in vitro. Optimisation studies revealed that post-harvest decay was more effectively reduced with B megaterium applied as a fine spray compared to dip application. It was found that 10⁸ cells/ml B licheniformis was the most effective antagonist concentration to reduce post-harvest decay, while all concentrations (10⁶, 10⁷ and 10⁸ cells/ml) were equally effective in reducing post-harvest infections. Additives (Agral 90 and L-alanine and glucose) were equally effective in enhancing the ability of B stearotermophilus to reduce litchi post-harvest fruit infection. Antagonists applied as a dip singly or in a mixture were more effective in reducing decay, post-harvest infection and fruit browning, than a warm water Benlate treatment. B subtilis (originally isolated from the avocado phylloplane) was also more effective in reducing litchi post-harvest fruit infection when compared to the Benlate chemical treatment.

Summary:

• The study isolated microbial epiphytes from chemically sprayed and unsprayed litchi trees, identifying three promising Bacillus antagonists: Bacillus stearothermophilus, Bacillus megaterium, and Bacillus licheniformis.
• These Bacillus isolates effectively inhibited multiple litchi post-harvest pathogens in vitro, including Phomopsis sp, Pestalotia sp, Alternaria alternata, Penicillium sp., and seven unidentified pathogens.
• Optimization studies showed that Bacillus megaterium applied as a fine spray reduced post-harvest decay more effectively than dip application.
• Bacillus licheniformis at a concentration of 10⁸ cells/ml was most effective in controlling decay, whereas all tested concentrations (10⁶, 10⁷, 10⁸ cells/ml) were equally effective against post-harvest infections.
• Additives such as Agral 90, L-alanine, and glucose did not significantly enhance the efficacy of Bacillus stearothermophilus in reducing infections.
• Antagonists applied either singly or in mixture as dips were more effective at reducing decay, infection, and fruit browning than warm water Benlate (chemical) treatments.
• Bacillus subtilis, isolated from avocado phylloplane, was less effective at controlling decay but reduced secondary infections better than Benlate chemical treatment.
• The study found biological control using these Bacillus species to be a promising alternative to chemical fungicides like Benlate, which have environmental and market concerns.
• Effective biological control was closely linked to antagonist concentration and application method, with fine spray delivery preferred for Bacillus megaterium.
• The research emphasized the importance of using naturally occurring antagonists from the target crop for consistent effectiveness.
• Ultimate commercial adoption would require registration of Bacillus antagonists and further evaluation of post-harvest application methods for consistency.
• The study relates the findings to similar successes in biological control for avocado and mango post-harvest diseases.
• Biological control offers a sustainable disease management strategy amid rising restrictions on agrochemical use in fresh produce export markets.