Antifungal potential of extracts produced from decomposed agricultural wastes by Bosea thiooxidans

Abstract

This work aimed to produce antifungal bioactive compounds from agro-wastes using cellulolytic bacteria, and to evaluate their in vitro and in vivo antifungal activities against faba bean damping off disease caused by Rhizoctonia solani. To achieve this purpose, a total of 34 rhizospheric bacterial isolates were screened for their abilities to degrade cellulosic compounds. The bacterial isolate which gave the best cellulolytic activity was identified as Bosea thiooxidans, according to its morphological, biochemical characteristics, and according to its 16S rRNA sequencing. Five native plants remains including; Pomegranate peel, chili waste, prickly peel, olive leaves and garlic stalks, were hydrolyzed by the selected cellulolytic B. thiooxidans strain UAB7, and their extracts were tested for in vitro antifungal potential against a number of fungal phytopathogens mainly; Rizoctonia solani, Fusarium moniliform; Pythium sp. and Phytophothora sp. Extracts of the decomposed garlic and olive wastes gave inhibition percentages ranging from 25-100%, against the tested fungal pathogens. Transmission electron microscopy (TEM) showed cyto-morphological alterations and empty cavities in hyphae of the treated R. solani. Moreover, qualitative and quantitative analyses of the phenolic compounds present in the tested extracts were carried out. Results showed that among the tested phenolic compounds, kaempferol and phenanthrene were more abundant in the decomposed garlic and olive extracts, respectively. The fermented garlic and olive extracts were evaluated for their in vivo potency to suppress the damping off disease of faba bean caused by R. solani. Faba bean plants treated with the fermented garlic and olive extracts demonstrated significantly better disease suppression, compared to the infested control. Furthermore, bands recovered through the electrophoretic patterns of the superoxide dismutase and peroxidase isozymes in the infested control plants, showed wide differentiation in their intensities and forms, compared to the healthy and the treated plants.