Bioprospecting actinobacteria of Assam for some rice disease management and growth promotion

Abstract

Actinobacteria, an important group of Gram positive bacteria are potent newlineproducers of wide variety of secondary metabolites with diverse biological activities newlineincluding biocontrol and plant growth promotion abilities. The members of the genus newlineStreptomyces are especially prolific as they alone constitute 50% of the total soil newlineactinobacteria and 18% of all biologically active secondary metabolites(nearly 7600 out newlineof 43,000) known so far. The present investigation was undertaken to explore potent newlineactinobacterial strains to contain two major rice diseases viz. sheath blight (ShB) and newlinebacterial leaf blight (BLB). Total seventy five isolates of actinobacteria were isolated newlineand their morphological, biochemical and molecular characterization were carried out. newlineAmong twelve antagonistic actinobacterial isolates observed in vitro, isolate Act 116 newlineand Act 119 recorded the maximum inhibition of ShB pathogen Rhizoctonia solani and newlineBLB pathogen Xanthomonas oryzae pv. oryzae by 66.7% and 26.3%, respectively. newlineScanning electron microscopy of these two isolates showed rectiflexible and newlineretinaculiaperti type of polysporous spore chains. Molecular identification of Act116 newlineand Act 119 done through 16S rRNA gene sequencing revealed the strains as newlineStreptomyces corchorusii and S. sasae, respectively. The partial gene sequences of the newlinetwo isolates were submitted to NCBI GenBank (GenBank No.KY393359.1 and GenBank newlineNo. MH988751.1). The pot culture and field experiments showed significant reduction newlineof per cent disease index (PDI) of ShB and BLB of rice (cv. Mahsuri) in strain Act newline116 and Act 119 treated plants. The application of actinobacteria Act 116 and Act newline119 as seed treatment, root dip and foliar spray could reduce PDI of ShB and BLB to newline24.6% and 30.8%, respectively over control (70.4 and 66.7 PDI, respectively). These newlinecombinations were also resulted in significant plant growth promotion. In field newlineexperiments, the microbial population increased in treated plots compared to control. newlineSignificant uptake of nitrogen, phosphorous and potash were observed in actinobacteria newlinetreated plots compared to control. The crude bioactive compounds extracted were newlineanalyzed through LCMS and revealed the possible presence of antibiotic compounds newlinelike Difloxacin, Dicloxacillin, Nystatin, Tetracycline and Doxycyline. Hence, it can be newlineinferred from the present study that actinobacterial strains Act 116 and Act 119 have newlinesignificant biocontrol potential against the two major rice diseases ShB and BLB, newlinerespectively and can be efficient candidates for management of other plant diseases newlinealso. newline