P. KISHORE VARMAVANAPALLI VASANTHI2023-12-182023-12-182023-12-18D6444https://krishikosh.egranth.ac.in/handle/1/5810203705Present study was undertaken to evaluate antagonistic potential of microbial consortia against groundnut stem rot. A total of sixteen fungal and fourteen bacterial bioagents were collected from Department of Plant Pathology, Agricultural College, Bapatla and Agricultural Research Station, Kadiri. Three fungal bioagents-T19007 (80.00%), T19012 (69.26%), T19015 (82.59%) and, three bacterial bioagents- PGP-1 (60.37%), PGP-2 (58.89%) and PGP-13 (73.33%) were found potential in vitro inhibiting S. rolfsii radial growth. The volatiles and non volatiles produced by six potential bioagents inhibited the radial growth of pathogen to varying extents. Volatile metabolites from isolates, PGP-1 and PGP-2 completely inhibited the radial growth of the pathogen.The nonvolatile metabolites (culture filtrate) of T19015 were found to be effective with 79.81 to 83.33% inhibition when tested at 10-30% concentration against S.rolfsii in vitro. Based on 16S-23S rRNA gene sequencing and their analysis through BLASTn search in NCBI database, the potential isolate PGP-13 was identified as Bacillus subtilis with 99.20% similarity. While the characterization of potential fungal isolates through Internal Transcribed spacer (ITS) region gene sequencing revealed that T19007 and T19012 isolates were closely related to Trichoderma asperellum with 95.67% and 98.37% similarity, whereas T19015 was closest match with Trichoderma spp. with 100% similarity. Biochemical characterization of all 14 bacterial isolates revealed that four isolates were tested positive for IAA production and only one isolate produced HCN and none of the isolates were tested positive to siderophore production, cellulase and chitinase activity. While, eight among sixteen fungal isolates were tested positive for cellulase activity and all the isolates were found negative to chitinase activity. The compatibility studies among three potential bacterial antagonists (PGP-1, PGP-2 and PGP-13) revealed that PGP-2+PGP-13 isolates were compatible with each other and two combinations (T19012+ T19015, T19007+ T19015) among three potential fungal antagonists were compatible. Whereas compatibility between potential fungal and bacterial antagonists revealed that the fungal isolate T19012 isolate was compatible with two bacterial isolates PGP-2 and PGP-13. The most suitable and effective isolates were developed into talc-based formulations, and their comparative biocontrol efficacy was assessed in a greenhouse condition. All of the treatments outperformed the pathogen-inoculated control in terms of preventing disease, promoting plant growth, and germination. When seeds were treated with a combination of bioagents rather than a single inoculant, the maximum levels of plant growth and disease control were attained. Fungal consortia (T19012+T19015), when used as a seed treatment alone or in combination with soil application, were found to be more effective than individual and other consortium treatments, potentially offering an alternative to fungicide treatment.EnglishThesis