In vitro activity of Bacillus and Trichoderma species in the management of crucial bacterial plant diseases

This study aimed to screen isolates of Bacillus and Trichoderma spp. for antagonistic activity against Ralstonia solanacearum, Xanthomonas campestris pv campestris, and Pseudomonas sp. in vitro. Twenty-eight Trichoderma and nineteen Bacillus isolates were used as antagonists. Molten nutrient agar was seeded with 2×108 CFU/ml of each pathogen, and the paper disc method was used to test the efficacy of the antagonists. Filter paper discs (5mm diameter) soaked for 10 minutes in Bacillus broth and 5mm discs of actively growing Trichoderma on potato dextrose agar were placed on the seeded media. Antagonistic activity was assessed by measuring the radius of the pathogen's zone of inhibition (ZOI) by the antagonist. The 10 Bacillus and 11 Trichoderma isolates that were tested had varied antagonistic activity against the pathogens. Trichoderma isolate T1 was the most potent in inhibiting the growth of R. solanacearum, with a mean ZOI measuring 13.5mm. In contrast, Bacillus isolate CB64 was the best antagonist, with a mean ZOI measuring 4.3mm. Trichoderma isolate T28 and Bacillus isolate CA5 showed the highest ZOI of 15.2mm and 6.6mm, respectively, against X. campestris. The antagonists screened gave lower activity against Pseudomonas sp. compared to other pathogens.