Screening of plant growth promoting rhizobacteria for antifungal activity against Fusarium oxysporum

Aim: New species of Plant Growth Promoting Rhizobacteria (PGPR), with varying growth promoting and biocontrol ability are often being discovered. They facilitate plant growth either directly by secreting nutrients and hormones or indirectly by providing defence mechanism to the plant. The present study was undertaken to isolate PGPR from the rhizosphere of Solanum lycopersicum and Arachis hypogaea, and test their growth promoting ability and antifungal activity against Fusarium oxysporum. Methodology: PGPRs were isolated from the rhizosphere of S. lycopersicum and A. hypogaea by serial dilution of the rhizospheric soil and identified by 16s rDNA sequencing. The isolates were analysed for antifungal activity against F. oxysporum, indole 3-acetic acid (IAA) production and phosphate solubilisation. For the growth promotion assay, aseptically grown Vigna radiata seedlings were dipped separately in isolated bacterial suspension of PGPR (10(9) CFU ml(-1)) and planted in autoclaved soil. Plants were irrigated with 50% Hoagland solution for every 48 hr and maintained at 25 +/- 2 degrees C with 16/8 hr of light and dark photoperiod. Growth promotion was examined in terms of differences in shoot length, root length, fresh weight and dry weight after 12 days of treatment. Results: Six isolates were found to have antifungal activity towards plant pathogen, F oxysporum. Five isolates showed similarity to Pseudomonas aeruginosa (B7-1, B11-5, B3-1, Rh-1, Rh-2) and one to Pseudomonas putida (B53). All six strains were able to produce IAA, where B53 and B13-1 showed the highest production compared to other strains. P. putida B53 demonstrated the highest plant growth promotion activity by significantly (p<0.05) increasing the growth of V. radiata plants as evidenced by increase in shoot length, root length, fresh and dry weight. Interpretation: The results obtained from the present study supports that PGPRs like Pseudomonas sp. could serve as potential eco-friendly bio-fertilizer and bio-fungicide.