Kannan, C.Sowmya, V.2023-12-152023-12-152023-09-26https://krishikosh.egranth.ac.in/handle/1/5810203530Rice stem rot and false smut diseases are caused by Sclerotium hydrophilum and Ustilaginoidea virens are major threat to the rice cultivation in almost all the major rice growing regions of the country. Detailed investigations were carried out on symptomatology, cultural and morphological characters of the pathogen, and their molecular identity through ITS primers and sequences were subjected to sanger sequencing and submitted to NCBI revealed similarity with Sclerotium hydrophilum SHPS1 and Ustilaginoidea virens UVPS1 (Accession number: OP480227, OP480796). Rhizosphere microflora were isolated and studied cultural, morphological and biochemical parameters and tested their antagonistic activity against the test pathogens under in-vitro and glass house conditions in susceptible rice varietiey TN1. Among fourteen isolates, P14 showed maximum production of IAA (7.37 μg/ ml), PS (67.26 μg/ml), siderophores (49.02 % siderophore units), biofilm production (1.35 OD600nm), and HCN (0.047 OD620nm). Molecular identification of potential isolate, nucleotide sequencing, NCBI BLAST, and phylogenetic analysis confirmed the identity of the bioagent as Pseudomonas otitidis POPS 1 (Accession number: ON782043). The antagonistic activity of isolated potential Pseudomonasisolate P14 along with standard bioagents viz., Trichoderma isolate (TAIK1) Bacillus isolate (BIK3) and Pseudomonas isolate (PIK1) collected from ICAR-IIRR culture collections were tested for their efficacy against S. hydrophilum and U. virens, their interaction was observed using scanning electron microscope (SEM). Phytohormones released from the bioagents were analysed using LC-ESI MS/MS. Potential isolate POPS1 along with TAIK1, BIK3 and PIK1 were screened for phytohormones secretion into their growth media. The selected potential bioagents (POPS1, TAIK1, BIK3, and PIK1) were tested against S. hydrophilum and U. virens under glass house conditions in rice susceptible variety TN1. The results showed that among different treatments, combination of four bioagents consortia was most effective in promoting plant growth viz., shoot length and root length in TN1 variety at two seasons (Rabi 2020-21 and Kharif 2021-22). Furthermore, secondary metabolites of PIK1 were extracted and characterized. A novel compound, 2-Methyl Pyrazine (2MP), was identified and confirmed using Nuclear magnetic resonance (NMR) spectroscopy and High-resolution mass spectrometry (HR MS). The purified 2MP and 6-Pentyl Pyrone (6PP) from TAIK1 were tested for their bio efficacy against S. hydrophilum and U. virens under in vitro conditions. To enhance the efficacy of the bioagents and metabolites, micro and nano encapsulated formulations were developed using extrusion, emulsification, and spray drying methods. The most efficient method was standardized, resulting in microencapsulated spores of TAIK1 and bacterial cells of PIK1, as well as nanoencapsulated 6PP and 2MP. The encapsulated formulations were then tested under in-vitro and in-vivo conditions against stem rot and false smut diseases using rice variety TN1 in a glasshouse. The stability and long-term storage ability of the microencapsulated formulations were demonstrated, with minimal decrease in population density over 90 days. The combination of microencapsulated TAIK1 and PIK1 exhibited the highest plant growth promotion and yield parameters. Nanoencapsulated 6PP showed strong inhibition of pathogen growth. The study also investigated changes in physiological parameters, soil enzymes, and chemical properties upon bioformulations treatment. Significant improvements were observed in plants treated with microencapsulated formulations, and there was a positive correlation between soil properties and plant growth promotion, and a highly negative relation with PDI percent of stem rot disease, indicated that change in soil properties upon encapsulated formulations has an impact on pathogen development and disease severity. Moreover, the research explored the impact of false smut disease and microencapsulated bioagent treatment on grain quality and panicle topology. The combination of MET + MEP treatment showed the most significant changes in these parameters. The whole-genome sequencing of PIK1 provided insights into its multifaceted activities and identified genes associated with various functions, including phytohormone production,secondary metabolite secretion, CRISPR/Cas genes, adhesion, detoxification, virulence-related, some volatiles and toxins, and antibiotic resistance. In conclusion, TAIK1 and PIK1 show promising potential as biocontrol agents against S. hydrophilum and U. virens in rice. The encapsulation of these bioagents enhances their efficacy, with nanoencapsulated 6PP being particularly effective in disease suppression. However, further research is needed for the commercial production and application of nano-encapsulated metabolite formulations at the farmer level. This thesis contributes valuable knowledge to the field of agricultural biocontrol and opens new avenues for sustainable disease management in rice cultivationEnglishThesis