Exemplifying rhizobacteria for growth stimulation and disease suppression in finger millet

Abstract

Of 111 rhizobacteria isolated from finger millet, 30 isolates exhibiting antagonism against Pyricularia grisea (22.22–44.44%) and Rhizoctonia solani (22.22–38.89%) were selected for functional characterization and in vitro interaction with pathogens. Appraisal of rhizobacteria for antimetabolites revealed HCN production by 3, ammonia production by all (0.80–4.39 µmol/ml) and H2S production by 5 isolates, while all produced siderophore (25.89–93.96%), 20 salicylic acid (3.12–54.46 µg/ml), 19 tested positive for glucanase, 17 for protease and 12 for amylase production. Culture filtrate of all the isolates inhibited growth of Rhizoctonia solani (23.33–81.11%) and Pyricularia grisea (19.35–53.22%). Role of thermostable metabolites in antagonism was observed with 21 isolates against Rhizoctonia solani (11.11–50.0%) and 24 against Pyricularia grisea (8.33–46.66%). Volatile antimetabolites of all the isolates retarded and inhibited growth of Pyricularia grisea (5.88–84.71%) and Rhizoctonia solani (5.5–83.33%), besides affecting mycelial quality and sclerotiation in Rhizoctonia solani. Metabolic extracts of 9 antagonists in ethyl acetate restricted the growth of Pyricularia grisea (8.88–20.80%) and of 10 inhibited Rhizoctonia solani (10.12–23.30%). Enlightening the involvement of bacterial growth regulators in plant growth stimulation, all isolates tested positive for IAA production (1.9–28.8 µg/ml in absence and 9.9–45.7 µg/ml in presence of tryptophan), 19 secreted ACC deaminase and 19 solubilized phosphate, while only 5 exhibited Zn-solubilization potential. Increase in plant height, root length, their fresh weight and chlorophyll content was recorded with seed priming under glasshouse condition.