Response of Melon Powdery Mildew to a Biocontrol Agent Bacillus velezensis M10 and Paraffin Oil

Abstract

The powdery mildew caused by air borne pathogen (Podosphaera fusca) is an important disease of cucurbits including melon (Cucumis melo L.) plants. Three antagonistic bacterial strains (M4, M10 and M11); isolated from the melon plants were tested for antagonistic activity against P. fusca and soil-borne pathogens of melon plants (Monosporascus cannonballus, Fusarium oxysporum f. spp. melonis, F. solani and Phomopsis spp.). All the three strains were identified as Bacillus velezensis based on sequence analysis of gyrase subunit A (gyrA) gene sequence. The bacterial strains showed significant antagonistic activity against soil and air borne pathogenic fungi. Among all strains, M10 showed a broad spectrum of mycelial growth inhibition against phytopathogenic fungi. The tested culture broth did not affect the pollen fertilization, flowering, fruit rot occurrence and fruit set development during blooming and cultivation season of the melon plants. The M10 culture broth stored for 3 and 6 months displayed biocontrol efficiency of 73.2 and 72.3%, respectively. Application of mixed solution of M10 culture broth + paraffin oil strongly suppressed the incidence and spread of powdery mildew. These results suggested that the combination of paraffin oil and B. velezensis M10 culture broth is an ecofriendly approach and possess strong biocontrol potential against melon powdery mildew and can also be used as antifungal agents for several plant pathogens. © 2021 Friends Science Publishers