Isolation, characterization and antifungal activity of Bacillus antagonistic bacteria from decomposing solid organic waste against Alternaria alternata and Fusarium oxysporum

Abstract

Plant diseases and pathogens affect agricultural crop production and sustainable development worldwide. Although chemical tools for controlling the diseases in crops are available, many of them exhibit serious impacts, especially on human and animal health and environmental pollution. Biological control could be an alternative approach towards managing disease in crops that promotes eco-friendly agricultural practices for sustainable environments. Alternaria and Fusarium diseases are a major source of loss to farmers all over the world; they affect many vital vegetable and food crops. This study sought to evaluate the in vitro antifungal properties of bacterial strains isolated from solid organic waste, green household waste and poultry droppings against Alternaria alternata and Fusarium oxysporum phytopathogenic fungi. The antagonist Bacillus bacteria were screened based on in vitro direct confrontation with A. alternata and F. oxysporum; among 110 isolates, 9 strains were selected for their antifungal potential against F. oxysporum and A. alternata. Using the 16S rRNA gene, the selected Bacillus bacteria were identified at the species through molecular identification as B. siamensis, B. amyloliquefaciens and B. subtilis. All antagonist strains were characterized for their possible mechanisms of biocontrol traits involved in these antifungal activities. Results showed that all selected Bacillus bacteria were found to be pectinase and amylase producers. However, only eight bacteria were found to produce proteases. Bioassays with the cell-free supernatants (CFSs) produced from B. amyloliquefaciens, B. siamensis and B. subtilis showed a significantly inhibited growth of F. oxysporum and A. alternata. Identifying effective biocontrol agents is challenging, especially in resource-limited settings, and their efficacy varies due to environmental and strain-specific factors. The findings indicate that antifungal compounds from B. siamensis, B. amyloliquefaciens and B. subtilis could be an alternative approaches as biocontrol agents to fungal diseases, improving crop yields and sustainable agriculture.