Studies on in vitro production of antimicrobial substances by Azotobacter chroococcum isolates/mutants

An attempt was made to study the in-vitro production of antimicrobial/antif ungal substances by various strains of Azotobacter chroococcum against vari ous plant pathogens. In addition, nature and role of these substances were studied on the germination and reduction in disease tinder) by Rhizoctonin solani in mustard crop. About 37 % of Azotobacter chroococcum isolates/muta nts showed a zone of inhibition against Rhizoctonia solani and 25 % against Xanthomonas campestris. Approximately 16% of isolates/mutants of A. chrooc occum were siderophore positive (sid(+)). The antimicrobial substances in A zotobacter were found to be extracellular, proteinaceous in nature and seem to be associated with some complex material also. Seed germination of must ard Brassica juncea (L.) cv. 'RH 30' increased when treated with A. chrooco ccum isolate/mutants (29, 18 and mala 27) alone and in combination with pla nt pathogens, i.e., Rhizoctonia solani and Xanthomonas campestris. A soil p ouch experiment conducted on B. juncea (L.) under pot house conditions show ed that root rot caused by R. solani was significantly reduced by all the s elected Azotobacter isolates/mutants. However, percent disease index was mi nimum with A. chroococcum 29, which was sid(-) also indicating that siderop hore production alone might not have a role in decreasing plant pathogenici ty.