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Abstract
The present work was undertaken with an objective to study the effect of culture filtrates and secondary metabolites of three Streptomyces spp. from black pepper rhizosphere having promising biocontrol and growth promoting traits on different developmental stages of pathogens like Phytophthora capsici and Sclerotium rolfsii. The study also focuses on identification of compounds responsible for the antimicrobial and growth promotive activity. Crude culture filtrate of IISRBPAct1 and IISRBPAct25 were found inhibitory to mycelial growth of P. capsici. Diluted culture filtrate of IISRBPAct1 (2 %) and IISRBPAct25 (5 %) were found inhibitory to the sporangia formation. Crude culture filtrate of IISRBPAct1 can completely inhibit the zoospore germination while it was inhibited to 98.6 % and 87 % by 10 % diluted extracts of IISRBPAct1 and IISRBPAct25 respectively. IISRBPAct1 showed 51.27 % inhibition of mycelial growth of S. rolfsii, while IISRBPAct25 and IISRBPAct42 showed 57.63 % and 26.90 % inhibition respectively. IISRBPAct1 is highly inhibitory to sclerotial formation even at 1 % concentration. The secondary metabolites of the three isolates were extracted in three solvent systems and their activity profile was detected and characterized by HPTLC. High resolution UPLC- (ESI)-QToF-MS analysis of the extracts revealed the presence of a vast array of antifungal compounds that supports the antimicrobial activity of culture filtrate and metabolites of the isolates.