Abstract
Vermicompost has become a promising alternative to chemical pesticide because of its disease suppression effect during these decades. However, the mechanisms by which vermicompost suppress plant disease are not well-understood. Antifungal compounds, which are released by beneficial organisms in the vermicompost, may play an important role in inhibiting plant pathogens; however, these mechanisms have not been widely examined. In this study, Sterilized Water Extracts of bamboo vermicompost (SWE), using a 0.22-μm cellulose acetate filter, significantly (P Rhizoctonia solani AG1-IB on a Potato Dextrose Agar (PDA) plate. This suggests that antifungal compounds are present in bamboo vermicompost. The ethanol acetate (EtOAc) crude extracts of bamboo vermicompost showing antifungal activity were further separated. Two compounds were isolated from the EtOAc fraction of bamboo vermicompost and characterized as ergosterol peroxide (1) and (22E, 24R)-5α,8α-epidioxyergosta-6,9(11),22-trien-3β-ol (2). Their chemical structures and mass spectra were determined by nuclear magnetic resonance and mass spectrometry analyses. Ergosterol peroxide tested at 150, 300, 600, and 900 μg showed 13%, 22%, 34%, and 53% mycelial growth inhibition against R. solani AG1-IB, respectively. Because EtOAc crude extracts of the initial substrate materials of bamboo vermicompost did not inhibit mycelium growth of R. solani AG1-IB, antifungal compounds in the vermicompost may be released by microbes but not from the original substrates during vermicomposting.
Highlights
Seedling damping-off diseases caused by Rhizoctonia solani are economically important in a broad range of crops worldwide [1] [2]
Antifungal compounds, which are released by beneficial organisms in the vermicompost, may play an important role in inhibiting plant pathogens; these mechanisms have not been widely examined
We examined the effects of water extracts of bamboo vermicompost, sterilized with a Corning 0.22-μm cellulose acetate filter (SWE), on R. solani AG1-IB mycelium growth on potato dextrose agar (PDA)
Summary
Seedling damping-off diseases caused by Rhizoctonia solani are economically important in a broad range of crops worldwide [1] [2] This pathogen is difficult to control because of its ability to persist under adverse soil conditions, as it contains structures such as sclerotia that survives for several years in the absence of host crops and exhibits saprophytic activity, a wide host range, and versatility [3]. Several antagonistic bacteria and fungi, such as Bacillus subtilis, Streptomyces spp., Trichoderma sp., and Aspergillus sp., were isolated from vermicompost and shown to suppress soil-borne plant pathogens [8] [9] [10]. These microbes are well-known to produce diversity bioactive compounds including antifungal compounds. Houz.) showed the ability to suppress cucumber damping-off caused by R. solani AG1-IB [11]
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