Biocontrol Potential of Culture Filtrates of Sclerotium cepivorum Against Onion White Rot Disease

The present work was purposed to investigate the efficacy of culture filtrates periodic produced by Sclerotium cepivorum in vitro (15, 30, 45, 60 and 75 days) against onion white rot disease under laboratory and in vivo in the greenhouse along with how much effect on plant growth parameters. The incubation period needed for S. cepivorum to produce secondary metabolites was found as an important factor in control strategy using culture filtrate treatments. Results suggested that culture filtrates produced at different incubation periods, decreased linear growth, number and percentage of germination of well-developed sclerotia of the fungus also, increased the mean time of sclerotia onset. The least disease severity (16.67 %) was recorded with the treatment of culture filtrate 15 days old compared to infected control (91.67 %) and other used treatments. Sclerotia were not able to germinate with 15 days old filtrate at 100 % concentration for 72 hours of soaking. Screening of secondary metabolites by gas chromatography-mass spectrophotometry (GC-MS) revealed 30 compounds categorized into alkaloids, organosilicon, antioxidants, lipids, esters, alcohols and fatty acids. Under greenhouse experiment, treatment with 15 days old culture filtrate gave the best results in reducing disease severity, improving plant growth and increasing peroxidase and polyphenol oxidase enzyme activities compared with other treatments. Secondary metabolites of S. cepivorum in 15 days old filtrate could be a powerful alternative way to chemical fungicides. Further investigations are suggested to know which metabolite compound/s responsible about control process.