The root-knot nematode (RKN) causes significant yield loss in tomatoes. Understanding the interaction of biocontrol agents (BCAs)-nematicides-soil microbiomes and RKNs is essential for enhancing the efficacy of biocontrol agents and nematicides to curb RKN damage to crops. The present study aimed to evaluate the in vitro effectiveness of BACa and nematicide against RKN and to apply the amplicon sequencing to assess the interaction of Bacillus velezensis (VB7) and Trichoderma koningiopsis (TK) against RKNs. Metagenomic analysis revealed the relative abundance of three phyla such as Proteobacteria (42.16%), Firmicutes (19.57%), and Actinobacteria (17.69%) in tomato rhizospheres. Those tomato rhizospheres treated with the combined application of B. velezensis VB7 + T. koningiopsis TK and RKN had a greater frequency of diversity and richness than the control. RKN-infested tomato rhizosphere drenched with bacterial and fungal antagonists had the maximum diversity index of bacterial communities. A strong correlation with a maximum number of interconnection edges in the phyla Proteobacteria, Firmicutes, and Actinobacteria was evident in soils treated with both B. velezensis VB7 and T. koningiopsis TK challenged against RKN in infected soil. The present study determined a much greater diversity of bacterial taxa observed in tomato rhizosphere soils treated with B. velezensis VB7 and T. koningiopsis TK than in untreated soil. It is suggested that the increased diversity and abundance of bacterial communities might be responsible for increased nematicidal properties in tomato plants. Hence, the combined applications of B. velezensis VB7 and T. koningiopsis TK can enhance the nematicidal action to curb RKN infecting tomatoes.

Meloidogyne incognita, the root-knot nematode (RKN), a devastating plant parasitic nematode, causes considerable damage to agricultural crops worldwide. As a sedentary root parasite, it alters the root’s physiology and influences the host’s phytohormonal signaling to evade defense. The sustainable management of RKN remains a challenging task. Hence, we made an attempt to investigate the nematicide activity of Bacillus velezensis VB7 to trigger the innate immune response against the infection of RKN. In vitro assay, B. velezensis VB7 inhibited the hatchability of root-knot nematode eggs and juvenile mortality of M. incognita by 87.95% and 96.66%, respectively at 96 hrs. The application of B. velezensis VB7 challenged against RKN induced MAMP-triggered immunity via the expression of transcription factors/defense genes by several folds pertaining to WRKY, LOX, PAL, MYB, and PR in comparison to those RKN-inoculated and healthy control through RT-PCR. Additionally, Cytoscape analysis of defense genes indicated the coordinated expression of various other genes linked to immune response. Thus, the current study clearly demonstrated the effectiveness of B. velezensis VB7 as a potential nematicide and inducer of immune responses against RKN infestation in tomato.

The soil microbiome is crucial for maintaining the sustainability of the agricultural environment. Concerning the role of diverse mycobiomes and their abundance toward the suppression of root-knot nematode (RKN) infection in vegetable crops, our understanding is unclear. To unveil this issue, we examined the fungal microbiome in tomato rhizosphere augmented with bioagents challenged against RKN at taxonomic and functional levels. Composition of the mycobiome in tomato rhizosphere treated with Bacillus velezensis VB7 and Trichoderma koningiopsis TK differed significantly from the infected tomato rhizosphere. The abundance and diversity of fungal species, however, were significantly higher in the combined treatments of bioagents than for individual treatments. Fungal microbiome diversity was negatively correlated in the RKN-associated soil. Network analysis of the fungal biome indicated a larger and complex network of fungal biome diversity in bioagent-treated soil than in nematode-associated tomato rhizosphere. The diversity index represented by that challenging the RKN by drenching with consortia of B. velezensis VB7 and T. koningiopsis TK, or applying them individually, constituted the maximum abundance and richness of the mycobiome compared to the untreated control. Thus, the increased diverse nature and relative abundance of the mycobiome in tomato rhizosphere was mediated through the application of either T. koningiopsis TK or B. velezensis VB7, individually or as a consortium comprising both fungal and bacterial antagonists, which facilitated engineering the community composition of fungal bioagents. This in turn inhibited the infestation of RKN in tomato. It would be interesting to explore further the possibility of combined applications of B. velezensis VB7 and T. koningiopsis TK to manage root-knot nematodes as an integrated approach for managing plant parasitic nematodes at the field level.