Evaluation of antagonistic activity of DAPG-producing fluorescent pseudomonads from rhizospheres of Solanaceous crops for biocontrol of bacterial wilt

Pseudomonads produce a wide array of antimicrobial compounds including 2,4-diacetylphloroglucinol (DAPG), which possess a broad-spectrum antagonistic effect against phytopathogens. Rhizospheric soil samples were collected from the Solanaceous crops for isolation of fluorescent pseudomonads (FPs). Out of the 32 fluorescent bacterial isolates, 21 showed antagonistic activity against Ralstonia solanacearum (NAIMCC-B-01630) with the highest zone of inhibition at 38.33 mm. Among them, 11 bacterial isolates depicted the production of DAPG in Kings' B medium. DAPG production was detected by TLC and quantified through HPLC analysis. Moreover, the bacterial isolate OD13 exhibited higher DAPG production. Further, the presence of the DAPG-encoding phlD gene within the size of 629 bp and 725 bp was also validated through amplification. These bacterial isolates belonged to the genera Pseudomonas as confirmed by morpho-physiological characterization using the VITEK 2 system. The higher DAPG-producing bacterial isolate was identified as Pseudomonas aeruginosa by polyphasic approach with GenBank accession number OQ781265. Thus, the DAPG-producing rhizospheric Pseudomonas strains can be used as biocontrol agents for bacterial wilt. However, field study is highly essential before its successful application.