Antifungal activity of Streptomyces sp. SLR03 against tea fungal plant pathogen Pestalotiopsis theae

Objectives: The search for new biocontrol agents, especially from natural sources, to control plant pathogens is a key area in tea plant protection research. Methods: Starch casein nitrate (SCN) agar was used to isolate the actinomycetes from the soil samples. These isolates were tested with modified version of the dual-culture method for antagonistic activity against Pestalotiopsis theae. The most bioactive isolate of actinomycets has been identified by biochemical, phisological, and morphological characterisation. Bioactivity of Streptomyces sp. SLR03 metabolites was measured in vitro and in vivo. The extract was eventually analyzed by GC-MS. Results: For the first time, an attempt has been made to isolate actinomycete species with bio-control potential from the river soil samples. A total of one hundred and seven actinomycete strains isolated and were evaluated for antagonistic potential against Pestalotiopsis theae using a dual-culture assay. Among the strains isolated, one strain SLR03 that showed potential and it was characterized. Further, the strain SLR03 was evaluated for antagonistic activity against P. theae both in vitro and in vivo. In in vitro assay, 86.15% and 93.85% mycelial growth inhibition was observed with cell-free filtrate and ethyl acetate extract of Streptomyces sp. SLR03, respectively. The ethyl acetate extract was further evaluated for its biocontrol activity against P. theae, it exhibited 80.39% reduction of disease incidence compared to the control. Further, the ethyl acetate extract were analyzed using GC-MS. The GCMS chromatogram exhibited 24 intense peaks consistently with 19 different compounds, 10 of which contain antifungal activity. Conclusions: This present study illustrates that Streptomyces sp. strain SLR03 is a prospective candidature for forthcoming biological control programme. (C) 2020 The Author(s). Published by Elsevier B.V. on behalf of King Saud University.