Efficacy of Photorhabdus luminescens Supernatant in Controlling Meloidogyne incognita: A Potential Biocontrol Strategy for Root-Knot Nematodes

Root-knot nematodes, Meloidogyne incognita, pose significant challenges to agricultural productivity worldwide. Exploring biological control agents against these nematodes is crucial for sustainable agriculture. This study evaluates the nematicidal properties of different components of Photorhabdus luminescens subsp. luminescens, a symbiotic bacterium known for its biocontrol potential. We isolated and characterized symbiotic bacteria and assessed the nematicidal activity of P. luminescens subsp. luminescens culture broth, cell pellet suspension, and cell-free supernatant against M. incognita eggs and juveniles. The experiments involved varying concentrations (10, 25, and 50%) and exposure periods. Egg hatchability and juvenile mortality were assessed in vitro, and statistical significance was determined using one-way ANOVA and Probit analysis for LC50 calculations. The cell-free supernatant of P. luminescens demonstrated the highest efficacy in suppressing egg hatchability and inducing juvenile mortality across all tested concentrations. Specifically, a 50% supernatant concentration achieved 100% juvenile mortality and significantly reduced egg hatchability (p < 0.001). Lower concentrations of supernatant also displayed substantial nematicidal activity, far outperforming the cell pellet suspension and culture broth. The LC50 values further substantiated the potency of the supernatant, with a dramatic decrease from 10.78% at 12 h to 1.78% at 24 h, indicating a time-dependent release of active compounds. The findings highlight the potent nematicidal activity of the P. luminescens supernatant, offering a promising biocontrol strategy against M. incognita. This study supports further exploration and optimization of P. luminescens-based products as sustainable solutions for managing root-knot nematodes in agriculture.