Plant growth-promoting traits of Streptomyces with biocontrol potential isolated from herbal vermicompost

Three strains of Streptomyces (CAI-21, CAI-26 and MMA-32) were earlier reported by us as having potential for biocontrol of charcoal rot of sorghum, caused by Macrophomina phaseolina (Tassi) Goid., and plant growth promotion (PGP) of the plant. In the present investigation, the three Streptomyces were characterised for their physiological traits (tolerance of salinity, temperature, pH and resistance to antibiotics) and further evaluated in the field for their PGP of rice, grown by a system of rice intensification methods. All three Streptomyces were able to grow in NaCl concentrations of up to 12% (except MMA-32), at pH values between 5 and 13 and temperatures between 20 and 40 degrees C. They were highly resistant to ampicillin and trimethoprim (>800 ppm), sensitive to chloramphenicol, kanamycin and nalidixic acid (50-100 ppm) and highly sensitive to streptomycin and tetracycline (5-25 ppm). When evaluated for their PGP activity on seedlings of rice, % germination and shoot and root lengths were significantly enhanced over the control. In the field, the Streptomyces strains significantly enhanced the panicle length, filled grain numbers and weight, panicle weight, 1000 seed weight, tiller numbers, total dry matter, root length (39-65%), root volume (13-30%), root dry weight (16-24%), grain yield (9-11%) and stover yield (11-22%) over the control. In the rhizosphere soil (0-15 cm from root) at harvest, the population of actinomycetes was significantly enhanced as was microbial biomass carbon (27-83%) and nitrogen (24-43%), dehydrogenase activity (34-152%), available P (13-34%) and N (30-53%) and % organic carbon (26-28%). This study further confirms that the selected Streptomyces have PGP properties.