Biological Control of Fusarium oxysporum, the Causal Agent of Fusarium Basal Rot in Onion by Bacillus spp.

Abstract

<i>Fusarium oxysporum</i> is the main pathogen causing Fusarium basal rot in onion (<i>Allium cepa</i> L.), which incurs significant yield losses before and after harvest. Among management strategies, biological control is an environmentally safe and sustainable alternative to chemical control. In this study, we isolated and screened bacteria for antifungal activity against the basal rot pathogen <i>F. oxysporum</i>. Isolates 23-045, 23-046, 23-052, 23-055, and 23-056 significantly inhibited <i>F. oxysporum</i> mycelial growth and conidial germination. Isolates 23-045, 23-046, 23-052, and 23-056 suppressed the development of Fusarium basal rot in both onion seedlings and bulbs in pot and spray inoculation assays. Isolate 23-055 was effective in onion seedlings but exhibited weak inhibitory effect on onion bulbs. Based on analyses of the 16S rRNA and <i>rpoB</i> gene sequences together with morphological analysis, isolates 23-045, 23-046, 23-052, and 23-055 were identified as <i>Bacillus thuringiensis</i>, and isolate 23-056 as <i>Bacillus toyonensis</i>. All five bacterial isolates exhibited cellulolytic, proteolytic, and phosphate-solubilizing activity, which may contribute to their antagonistic activity against onion basal rot disease. Taken together <i>B. thuringiensis</i> 23-045, 23-046, 23-052, and 23-055 and <i>B. toyonensis</i> 23-056 have potential for the biological control of Fusarium basal rot in onion.