ISOLATION AND ASSESSMENT OF ANTAGONISTIC ABILITY OF SEVERAL BENEFICIAL BACTERIA FROM POMELO ORCHARD SOIL IN VINH LONG PROVINCE AGAINST Fusarium solani AND Sclerotium rolfsii

Abstract

The study isolated 20 root-associated Bacillus strains from 150 soil samples collected in pomelo orchards in Bình Minh Ward, Vĩnh Long Province. In vitro antagonism assays against Sclerotium rolfsii, causal agent of root rot, identified six strains - VLND‑0202, VLND‑0802, VLND‑0901, VLND‑1202, VLND‑1301, VLND‑2002 - that exhibited antagonistic activity above 70%. Further evaluation of these six strains against Fusarium solani, responsible for yellow‑leaf root rot, selected three strains (VLND‑0802, VLND‑1202, VLND‑1301) with strong antagonism at 9 days post inoculation, achieving inhibition efficiencies of 58.50%, 60.50%, and 66.50%, respectively. Moreover, all three selected root bacterial strains demonstrated phosphate‑solubilizing ability; at 7 days after placement, they formed uniform phosphate‑degrading clear zones of 10 mm diameter. These effective strains will be taxonomically identified and further tested for biocontrol efficacy under greenhouse conditions