Isolation and evaluation of bacterial endophytes against Sclerospora graminicola (Sacc.) Schroet, the causal of pearl millet downy mildew

Background Pearl millet remains prone to many diseases; among them downy mildew caused by Sclerospora graminicola (Sacc.) Schroet is economically more important. The use of endophytic bacteria for management of downy mildew of pearl millet as eco-friendly approach is increasing attention as sustainable alternative to pesticides. The objective of the present study was to isolate endophytic bacteria from roots of pearl millet cultivars and assess for biocontrol activity against Sclerospora graminicola. Results Thirty pearl millet root bacterial endophytes (PMRBEs) were isolated and screened in vitro for biocontrol activities such as: siderophore production, hydrogen cyanide (HCN) production and 1-amino cyclopropane-1-carboxylate (ACC) deaminase activity. Sixteen isolates possessed siderophore production potential, 3 isolates were found to be HCN producers, and 30% of the bacterial endophytes showed a good growth on ACC supplemented plates. On the basis of biocontrol activities, promising endophyte PMRBE6 was selected for seed treatment as well as a foliar spray to manage downy mildew of pearl millet in screen house experiment. The isolate PMRBE6 was found to be effective in managing downy mildew disease. Grain yield, test weight, plant height and average number of productive tillers were found to be maximum on inoculation of seeds of different pearl millet cultivars with PMRBE6, and the results were statistically significant as compared to control. Conclusions On the basis of biochemical characterization and partial 16S rRNA sequencing, the isolate PMRBE6 was identified as Bacillus subtilis strain PD4 (Accession no. MN400209). Pearl millet root bacterial endophyte (PMRBE6) exhibiting biocontrol activities could be exploited in friendly, sustainable organic agriculture.