Characterization of plant growth-promoting and disease suppressing abilities of certain actinomycetes isolated from groundnut rhizosphere
S. JACOB (1), H. K. Sudini (1). (1) ICRISAT, Hyderabad, India
Actinomycetes are widely used bacterial biocontrol agents in plant disease management. The present study focused on isolation and characterization of certain actinomycetes from groundnut rhizosphere for growth-promotion and pathogen suppressiveness. Dual culture studies were conducted to assess the antifungal abilities against aflatoxin producing fungi (<i>Aspergillus flavus</i>) and stem rot pathogen (<i>Sclerotium rolfsii</i>). Sixteen isolates showing high antagonism were further characterized for biocontrol and growth-promotion in groundnut. <i>In-vitro</i> antifungal assays indicated that 50% inhibition was exhibited by 10 isolates against <i>S. rolfsii</i> and more than 40% inhibition was shown by five isolates against <i>A. flavus</i>. Two superior isolates (RP1A-12 and RP1A-15) were selected based on fungal antagonism and crop growth promotion. Culture filtrates of RP1A-12 and RP1A-15 exhibited good antagonism against test pathogens, with crude extract of RP1A-15 showing complete inhibition of the mycelia at 1.5%. The HPLC chromatograms of RP1A-15 and RP1A-12 crude extracts showed eight and three peaks respectively. Separation of eight compounds in RP1A-15 was obtained with silica gel flash column chromatography. Bio-efficacy studies were conducted on the obtained fractions and results suggested one fraction significantly delayed the germination of sclerotia of <i>S. rolfsii</i>. Identification of these two isolates using 16S rRNA sequencing and bio-active fraction using LC-MS, NMR are in progress.
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