Protective effect of Bacillus species associated with Rumex dentatus against postharvest soil borne disease in potato tubers and GC-MS metabolite profile.

Potato is constantly exposed to various kinds of phytopathogens which cause diseases during the developmental stage and post-harvest storage. This investigation was designed to assay the anti-phytopathogen activity of bacterial endophytes and their suppressive effects on rot disease in potato. The study also aimed to screen isolates for their plant growth-promoting traits and establish GC-MS-based metabolite profile of the potent isolate. Endophytes were isolated from Rumex dentatus and identified based on 16S rRNA gene. They were screened in dual culture assay against fungal phytopathogens and the potent isolate was tested for its capability to suppress Fusarium rot disease in potato tubers. The mechanism of action of endophytes on the phytopathogens was assessed using scanning electron microcopy. Isolates were also screened in vitro to assay their capability to produce phytohormones, hydrolytic enzymes, and to solubilize phosphates. Endophytic isolates produced proteases with a diameter of halo zone ranging from 7 to 32 mm. Bacillus sp. KL5 exhibited the highest production of indole acetic acid (IAA) with the amount of 104.28 µg/mL and was the most potent antagonist of Fusarium oxysporum and Verticillium dahliae with an inhibitory percentage of 61.53 and 100%, respectively. It showed a reduction of potato rot disease severity by more than 50%. GC-MS of active fractions of KL5 showed the presence of dibutylphthalate and 2,4-di-tert-butylphenol as major metabolites. From this study, it is evident that endophytic Bacillus species from R. dentatus are potent antagonists of F. oxysporum and V. dahliae. Bacillus sp. KL5 is a potent inhibitor of pathogenic F. oxysporum in potato tubers and can be developed as a biocontrol agent.