Antagonistic Potential of Salt Tolerant Bacteria and Optimization of Their Culture Conditions for Enhancement of the Activity

Abstract

The antagonistic potential of bacteria is being applied to biocontrol the infectious diseases caused by pathogenic fungi in plants that are one of the major threats to the growth and productivity of crop plants. In the present study, bacterial strains were isolated from soil samples collected from the rhizosphere of Sorghum (Sorghum bicolor) and Wheat (Triticum aestivum). Microscopic analysis revealed that all three bacterial isolates were Gram-positive, rod-shaped and spore-forming. The isolates Bacillus subtilis BP171 and Bacillus amyloliquefaciens BP124 demonstrated salt tolerance up to 12% while Bacillus subtilis BP67 tolerated up to 10% of NaCl. All the three strains were screened against seven test pathogenic fungi like Bipolaris sorokiniana, Fusarium oxysporum, Aspergillus sp., Penicillium sp., Rhizoctonia solani, Aspergillus niger, and Fusarium sp. for their antagonistic activity. BP124 was found to be the most potent in comparison to BP67 and BP171. Bacillus amyloliquefaciens BP124 demonstrated significantly highest (p<.0001) inhibition percentage against Fusarium sp., (61%) and Fusarium oxysporum (60%). The optimization of various parameters like pH, temperature, inoculum size, agitation, carbon sources, and nitrogen sources was carried out to enhance the antagonistic potential of bacterial isolates. The results revealed that the bacterial isolates were able to demonstrate significantly highest (p<.0001) antagonistic potential when inoculum size required for the growth was 1ml, agitation rate at 150 rpm, while the medium of pH at 7.0 and 30o C incubation temperature. Starch as carbon source and peptone as nitrogen source supported significantly highest (p<.0001) antagonistic activity against all the fungal pathogens for all the bacterial isolates. Therefore, the study showed that appropriate and optimum fermentation conditions can be of great importance in enhancing the antagonistic potential of bacterial isolates.