Acidotolerant Streptomyces sp. MBRL 10 from limestone quarry site showing antagonism against fungal pathogens and growth promotion in rice plants

Abstract Acidotolerant Streptomyces sp. MBRL 10 isolated from limestone deposit site on Gauze’s medium No. 1 (pH 5.3) showed significant antagonism against the tested fungal pathogens. It exhibited the highest mycelial growth inhibition by diffusible and volatile compound(s) production against Rhizoctonia solani . Culture filtrates also exhibited significant inhibition zone but the inhibition activities vanished when sterilized. The strain produced chitinase, β-1,3-glucanase, lipase, protease and ammonia but not β-1,4-glucanase. It could produce 25 μg/ml of indole acetic acid, solubilize up to 140 μg/ml of phosphate with a concomitant decrease in pH of the medium. The bioactive actinomycete strain produced hydroxamate type of siderophore. Casamino acid was found to be the best medium for siderophore production (87% siderophore units). MBRL 10 showed the highest rice seedlings vigor index corresponding to an inoculum size of 0.3 × 10 8  cfu/ml. Strain treated rice seeds at an inoculum size of 0.3 × 10 8  cfu/ml showed higher germination percentage and significantly enhanced ( P  ⩽ 0.05) the growth of seedlings. Strain treated rice seedlings challenged with pathogens also exhibited higher germination percentages and significantly enhanced ( P  ⩽ 0.05) growth over seedlings challenged with pathogen alone in the absence of the bioinoculant. Rice plants treated with the strain significantly promote ( P  ⩽ 0.05) the growth under nethouse conditions.