Biological control of onion white rot disease using potential Bacillus subtilis isolates

Abstract

Abstract Background Onion (Allium cepa L.) is a very important vegetable crop all over the world, particularly in Egypt for local consumption and exportation. White rot disease is the most serious disease of Allium spp. caused by the soil-borne fungus Sclerotium cepivorum Berk. Results In this investigation, five tested isolates of Bacillus subtilis showed an antagonistic effect and significantly reduced the linear growth of the pathogen in vitro. B. subtilis isolates no. 2 and 4 caused the highest reduction of S. cepivorum growth, 75.78 and 74.33%, respectively, while isolate no. 3 was the least effective one, causing 66.67% growth reduction. Under field conditions at two successive seasons (2019/20 and 2020/21), all tested bioagent treatments reduced the percentage of infection than Folicure as an officially recommended fungicide. B. subtilis isolate no. 2 showed the highest efficacy (78.57 and 77.78%) followed by isolates no. 4 (74.29 and 72.22%), while B. subtilis isolate no. 3 showed the lowest efficacy (42.86 and 50.00%), respectively, for both successive seasons. All treatments increased dry onion bulb yield and improved its quality than the untreated control plants. The chemical changes of total carbohydrates, total nitrogen contents, total soluble solids (TSS %) and enzymes activity related to defense mechanisms in treated plants by biological treatments were considered. Conclusion This study aimed to find effective biological agents of B. subtilis isolates against the white rot of onion and evaluate their effect on yield parameters, components and quality.