Biological Control of Fusarium sp. NBRI-PMSF12 Pathogenic to Cultivated Betelvine by Bacillus sp. NBRI-W9, a Potential Biological Control Agent

Betelvine is prone to several fungal diseases including leaf spots, foot and root rot caused by Fusarium spp. due to humid conditions prevailing in fields. In the present study, a potent antagonistic bacterial endophyte and a virulent fungal pathogen were selected after rigorous screening of isolates from different betelvine varieties to provide an efficient biocontrol strategy in cultivation of betelvine. Wild varieties of crops are a rich source of untapped endophytes. Of the four betelvine varieties used for isolations and screening, the wild variety was richest in endophytic populations. Using 16S rRNA sequencing, the selected antagonist was identified as Bacillus sp. (NBRI-W9). The pathogen, virulent against cultivated varieties, was identified as Fusarium sp. (NBRI-PMSF12) using ITS 1 and 2 region sequencing. Under in vitro and field conditions, NBRI-W9 was able to induce early rooting, provide plant growth promotion, increase leaf size and yield (leaf number) and provide biocontrol against the Fusarium sp. infection. NBRI-W9 treatments showed bacterial colonization on the leaf surface preferably in the vicinity of pearl glands and the collenchyma region in scanning electron microscope (SEM) studies. NBRI-W9 was observed to directly enter the leaf by degrading cell walls and colonize the subcellular layers. SEM analysis showed direct confrontation of NBRI-W9 with Fusarium on the leaf surface and in the collenchyma region as one of the probable modes of biocontrol.