ISOLATION, SCREENING AND CHARACTERIZATION OF AZOTOBACTER FROM RHIZOSPHERIC SOILS FOR DIFFERENT PLANT GROWTH PROMOTION (PGP) & ANTAGONISTIC ACTIVITIES AND COMPATIBILITY WITH AGROCHEMICALS: AN IN VITRO STUDYJ. Sai Prasad, R. Subhash Reddy, P. Narayan Reddy and A. Uma Rajashekar
Plant Growth Promoting Rhizobacteria (PGPR) are known to influence plant growth by various direct or indirect mechanisms. In search of efficient PGPR strains with multiple activities, a total of twenty four (24) Azotobacter isolates of plant growth promoting rhizobacteria from rhizospheric soils of Rajendranagar were isolated and identified based on their morphological, physiological and biochemical characteristics using standard methods. These test isolates were screened in vitro for PGPR properties like phosphate solubilization, siderophore, IAA, HCN productions, antagonistic activity against Rhizoctonia solani, Sclerotium rolfsii and compatibility with commonly used pesticide molecules. The results revealed that 91.66% Azotobacter isolates showed positive for ammonia production, 58.3% for phosphate solubilization, 83.33% for siderophores, 54.16% for HCN and 29.16% for IAA productions. Out of 24 Azotobacter isolates 3 isolates CBuAB1, CBpAB2, SBpAB1 showed inhibition potential against both Rhizoctonia solani and Sclerotium rolfsii. The maximum per cent inhibition against Rhizoctonia solani was showed by CBuAB1, CBpAB2, CRpAB1 and ABpAB1 with 36.05%. The maximum per cent inhibition against Sclerotium rolfsii was showed by SBpAB2 (38.25%). The isolate that showed maximum inhibition potential against Rhizoctonia solani was also inhibitory to Sclerotium rolfsii to a lesser extent based on per cent inhibition and vice versa. Hence it can be inferred that the Azotobacter isolates CBuAB2, CRuAB2, CRpAB1, CRpAB2, SBuAB2, SBpAB2, SRuAB1, ARuAB1 and ARpAB1 could be considered for their bio control activity. Among the pesticides tested Azoxystrobin (fungicide), Imidacloprid (insecticide) were found to inhibit Azotobacter at recommended / half recommended dosage. However other fungicides, insecticides and all herbicides were compatible with all the isolates tested. Out of the 24 isolates tested for their compatibility with the four each of the fungicides, insecticides, herbicides based on their PGPR attributes and antagonistic activity, the isolate of Azotobacter isolate CBuAB1 showed potential as PGPR.
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