Exploring actinomycetes and endophytes of rice ecosystem for induction of disease resistance against bacterial blight of rice

Biocontrol agents and plant growth promoting microbes have emerged as promising tools for the management of plant diseases and in sustainable crop production. The present study was made to explore the potential metabolites of actinomycetes and endophytes of rice (Oryza sativa L.) and to assay the induced defence reactions in rice plants against bacterial blight (BB) of rice (Xanthomonas oryzae pv. oryzae). In-vitro studies revealed that few promising rhizospheric Streptomyces (S. fimicarius and S. laurentii) and endophytes (Pseudomonas putida and Metarhizium anisopliae) could suppress Xoo effectively in dual culture assay. P. putida + S. fimicarius + S. laurentii showed the highest (58.71%) inhibition of BB. Multiple growth promoting characteristics were assayed for these effective isolates. The effectiveness of the cell suspension (107 cfu/ml) of P. putida, M. anisopliae, S. fimicarius and S. laurentii in suppressing BB of rice was tested in planta by applying as seed treatment, root treatment, soil treatment and spray application. Lowest disease incidence was observed in plants treated with the combination of P. putida + S. fimicarius + S. laurentii (10.29%) as compared to other treatments. To understand the resistance mechanisms of rice plants against Xoo, few effective secondary metabolites were assayed where the total phenol content of the treated plants showed higher concentration (2.52%). Antibiotics were recorded at a higher peak of retention time, such as pyrisulfoxin B (12.26 min), APHE 4 (13.42 min), kanamycin C (22.22 min), nitracidomycin B (15.40 min), clavulanic acid (7.89 min), neothramycin A (16.22 min), nitracidomycin A (17.78 min) and furaquinocin E (24.74 min).