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Subject: Plant Pathology × Author: Gogoi, Nripen Kumar × End date: 2022 × Start date: 2020 × Type: Thesis × Thesis Type: Ph.D ×
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    ThesisItemOpen Access
    BIOPROSPECTING ACTINOBACTERIA OF ASSAM FOR SOME RICE DISEASE MANAGEMENT AND GROWTH PROMOTION
    (2020-01) Gogoi, Nripen Kumar; Bora, L.C.
    Actinobacteria, an important group of Gram positive bacteria are potent producers of wide variety of secondary metabolites with diverse biological activities including biocontrol and plant growth promotion abilities. The members of the genus Streptomyces are especially prolific as they alone constitute 50% of the total soil actinobacteria and 18% of all biologically active secondary metabolites(nearly 7600 out of 43,000) known so far. The present investigation was undertaken to explore potent actinobacterial strains to contain two major rice diseases viz. sheath blight (ShB) and bacterial leaf blight (BLB). Total seventy five isolates of actinobacteria were isolated and their morphological, biochemical and molecular characterization were carried out. Among twelve antagonistic actinobacterial isolates observed in vitro, isolate ‘Act 116’ and ‘Act 119’recorded the maximum inhibition of ShB pathogen Rhizoctonia solani and BLB pathogen Xanthomonas oryzae pv. oryzae by 66.7% and 26.3%, respectively. Scanning electron microscopy of these two isolates showed rectiflexible and retinaculiaperti type of polysporous spore chains. Molecular identification of ‘Act116’ and ‘Act 119’ done through 16S rRNA gene sequencing revealed the strains as Streptomyces corchorusii and S. sasae, respectively. The partial gene sequences of the two isolates were submitted to NCBI GenBank (GenBank No.KY393359.1 & GenBank No. MH988751.1). The pot culture and field experiments showed significant reduction of per cent disease index (PDI) of ShB and BLB of rice (cv. Mahsuri) in strain ‘Act 116’ and ‘Act 119’ treated plants. The application of actinobacteria ‘Act 116’ and ‘Act 119’ as seed treatment, root dip and foliar spray could reduce PDI of ShB and BLB to 24.6% and 30.8%, respectively over control (70.4 and 66.7 PDI, respectively). These combinations were also resulted in significant plant growth promotion. In field experiments, the microbial population increased in treated plots compared to control. Significant uptake of nitrogen, phosphorous and potash were observed in actinobacteria treated plots compared to control. The crude bioactive compounds extracted were analyzed through LCMS and revealed the possible presence of antibiotic compounds like Difloxacin, Dicloxacillin, Nystatin, Tetracycline and Doxycyline. Hence, it can be inferred from the present study that actinobacterial strains ‘Act 116’ and ‘Act 119’ have significant biocontrol potential against the two major rice diseases ShB and BLB, respectively and can be efficient candidates for management of other plant diseases also.