Potential of Pseudomonas and Bacillus Isolates as Biocontrol Agents Against Fusarium Wilt of Eggplant

ABSTRACT

Plant growth-promoting rhizobacteria (PGPR) are beneficial bacteria found on plant roots that induce growth by a wide variety of mechanisms. Ten isolates of Pseudomonas and Bacillus were isolated from eggplant rhizosphere soil and evaluated for their volatile compound efficacy against mycelial growth of Fusarium oxysporum f. sp. melongenae (Fomg) and tested for their ability to colonize eggplant (Solanum melongena L.) roots in vitro. PGPR strains inhibited mycelial growth of the target pathogen and the percentage of inhibition varied from 38% to 72% by means of inhibitory activities. Pseudomanas aeruginosa (P07–1) and P. putida (P11–4) were determined to be successful colonizers in eggplant seedlings. Also, a pot experiment was conducted to assess the induced resistance to Fusarium wilt of eggplant by PGPR strains. Among the PGPR isolates, P. aeruginosa (P07–1), P. putida (P11–4), P. aeruginosa (85A-2), Bacillus amyloliquefaciens (76A-1) and B. cereus (B10a) significantly reduced Fusarium wilt disease incidence by up to 85%. However, their combination was not more effective in suppressing the disease than the application of those isolates alone. The induction of peroxidase (POX, EC 1.11.1.7) and polyphenol oxidase (PPO, EC 1.14.18.1) enzymes was found to be significantly higher in comparison with the control group. Similarly, the proline levels in eggplants showed an increasing trend with the above isolates. However, catalase (CAT, 1.11.1.6) activity was not found to significantly contribute to the induced resistance mechanism. This study revealed that the promising PGPR isolates could be potentially very useful for the biocontrol of Fomg via enhancing disease resistance in eggplant plants.

Keywords:

• PGPR
• Pseudomonas spp.
• Bacillus spp.
• Fusarium wilt
• defense enzymes
• eggplant