Aim: To screen and evaluate the biocontrol potential of Paenibacillus strains against disease complex caused by Meloidogyne incognita and Fusarium oxysporum f. sp. lycopersici interactions. Methods and Results: Paenibacillus strains were collected from rotten ginseng roots. The strains were tested under in vitro and pots for their inhibitory activities, and biocontrol potential against disease complex caused by M. incognita and F. oxysporum f. sp. lycopersici on tomato. In in vitro experiments, among 40 tested strains of Paenibacillus spp., 11 strains showed antifungal and nematicidal activities against F. oxysporum f. sp. lycopersici and M. incognita, respectively. Paenibacillus polymyxa GBR-462; GBR-508 and P. lentimorbus GBR-158 showed the strongest antifungal and nematicidal activities. These three strains used in pot experiment reduced the symptom development of the disease complex (wilting and plant death), and increased plant growth. The control effects were estimated to be 90-98%, and also reduced root gall formation by 64-88% compared to the untreated control. Conclusion: The protective properties of selected Paenibacillus strains make them as potential tool to reduce deleterious impact of disease complex plants. Significance and Impact of the Study: The study highlights biocontrol potential of Paenibacillus strains in management of disease complex caused by nematode-fungus interaction.
In the present work 25 strains of Paenibacillus polymyxa isolated from rotted ginseng roots were screened for their antimicrobial activity against Phytophthora capsici in vitro. Based on antimicrobial activity, 15 strains categorized as strongly antimicrobial, among them GBR‐462 was found as the most active, and five strains each as weekly antimicrobial and no antimicrobial. Antimicrobial activity was influenced by the initial inoculum density, as strains of P. polymyxa with a strong antimicrobial activity (including P. polymyxa GBR‐462) showed the antimicrobial activity against P. capsici and could form biofilm only when they were applied at the higher initial inoculums, 108 cfu/ml. No inhibitory effect was noted on the mycelial growth and zoospore germination of the pathogen when applied at the lower inoculum density of 106 cfu/ml of P. polymyxa GBR‐462. However, sporangium formation and zoospore release was significantly inhibited at the lower inoculum density. Also light and electron microscopy revealed the structures of sporangia aberrant with no or few healthy nuclei, indicating sporangium and zoospore formation inhibited at the lower inoculum density. Application of P. polymyxa GBR‐462 into potted soil suppressed disease progression as well as disease severity; disease severity was reduced by 30% as compared to untreated pots, suggesting P. polymyxa GBR‐462 could be a potential biocontrol agent against Phytopthora capsici.
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