Evaluation of seed associated endophytic bacteria from tolerant chilli cv. Firingi Jolokia for their biocontrol potential against bacterial wilt disease

Abstract

In this study, the seed endosphere of a bacterial wilt tolerant chilli cv. Firingi Jolokia was explored in order to find effective agents for bacterial wilt disease biocontrol. A total of 32 endophytic bacteria were isolated from freshly collected seeds and six isolates were selected based on R. solanacearum inhibition assay. These isolates were identified as Bacillus subtilis (KJ-2), Bacillus velezensis (KJ-4), Leuconostoc mesenteroides (KP-1), Lactococcus lactis (LB-3), Bacillus amyloliquefaciens (WK-2), and Bacillus subtilis (WK-3) by 16S rRNA gene sequencing. In the in planta R. solanacearum inhibition assay carried out by seedling root bacterization method, Bacillus subtilis (KJ-2) exhibited highest biocontrol efficacy of 86.6 % on 7th day post R. solanacearum inoculation and a minimum biocontrol efficacy of 52.9 % was noted for Leuconostoc mesenteroides (KP-1). GC-HRMS analysis detected several known antimicrobial compounds in the extract of the culture supernatant of Bacillus subtilis (KJ-2); which may contribute to inhibition of R. solanacearum. In the growth promotion assay conducted using these isolates, only two of them namely Bacillus subtilis (KJ-2) and Bacillus amyloliquefaciens (WK-2) showed growth promotion in true leafed tomato plants. All the selected seed endophytic isolates were able to control bacterial wilt of tomato at the seedling stage and Bacillus subtilis (KJ-2) was found to be most effective in controlling the disease. The results of the present study highlighted that seed endosphere of bacterial wilt tolerant cultivar is a rich source of R. solanacearum antagonizing bacterial isolates.