Nematicidal and plant growth-promoting potential of the cell-free culture supernatant of Bacillus megaterium in tomato under Meloidogyne incognita infection: an in vitro and in vivo study.

This study evaluated the nematicidal efficacy and plant growth-promoting potential of the cell-free bacterial culture supernatant (BCS) of Bacillus megaterium in mitigating Meloidogyne incognita-induced stress in Solanum lycopersicum under both in vitro and in vivo conditions. Mortality bioassay revealed that cell-free BCS induced a clear dose- and time-dependent nematicidal response, with maximum juvenile mortality of 100% observed at 100% concentration within 96 h (p < 0.001). B. megaterium was characterized for plant growth-promoting and biocontrol traits including indole-3-acetic acid (IAA) synthesis, ammonia production, phosphate solubilization, hydrogen cyanide (HCN) production and protease activity. The experiments conducted on 10-day-old seedlings (in vitro) and 45-day-old plants (in vivo) revealed that nematode infestation impaired morphological attributes, reduced photosynthetic pigments and elevated stress indices. However, cell-free BCS treatment markedly reduced galling, enhanced growth parameters, lowered stress markers and modulated antioxidant responses along with increased levels of secondary metabolites. Confocal microscopy analyses revealed enhanced cell viability and increased glutathione accumulation in cell-free BCS treated seedlings. This study provides new insights into morphological, biochemical and physiological responses of M. incognita-stressed S. lycopersicum treated with cell-free BCS and highlights the potential of B. megaterium as a sustainable biocontrol and plant growth- promoting agent under controlled conditions.