Efficiency of bacterial biosurfactant for biocontrol of Rhizoctonia solani (AG-4) causing root rot in faba bean (Vicia faba) plants

Biosurfactants are a structurally diverse group of surface-active compounds produced by microorganisms, with numerous applications in different fields. In the present study, we evaluated the antifungal activity of a biosurfactant produced by Bacillus licheniformis against Rhizoctonia solani AG-4 that causes root rot in two cultivars of Vicia faba (Nubaria 1 & Sakha 1). Molasses and yeast extract as carbon and nitrogen sources exhibited maximum emulsification activity and fungal growth inhibition. Treatment with biosurfactant decreased the disease incidence from 62.11 to 20.00% in cv. Nubaria 1 and from38.93 to 16.51% in case of cv. Sakha 1. Results revealed that growth parameters, photosynthetic pigments and endogenous phytohormones were markedly inhibited in faba bean, particularly in cv. Nubaria 1 plants, due to the root rot disease. Moreover, infection with R. solani caused an increase in lipid peroxidation content, non-enzymatic (phenolic and flavonoids compounds) and enzymatic antioxidants contents (phenylalanine ammonia lyase) as compared with healthy control plants. Biosurfactant application to the healthy and infected plants enhanced all the mentioned parameters except the lipid peroxidation content which showed significant reduction. Electrophoretic patterns of peroxidase, polyphenol oxidase and superoxide dismutase isoenzymes showed wide variations in their intensities and densities among all treatments. Peroxidase and polyphenol oxidase showed increased activities in cv. Sakha 1 by BS application. It appears that application of bacterial biosurfactant was able to enhance the biological control of root rot disease of faba bean plants.