Assessing the Role of Melia azedarach Botanical Nematicide in Enhancing the Structure of the Free-Living Nematode Community

In a greenhouse experiment, we studied the impact of Melia azedarach ripe fruit water extract (MWE), Furfural (a key ingredient of M. azedarach), and the commercial nematicide Oxamyl (Vydate® 10 SL) on the soil free-living nematode community. Treatments were applied every 20 days for two months, and soil samples were collected 3 days after the last application (3DAA) and at the end of the cultivation period (34DAA). We assessed short- and long-term effects on nematode community structure, metabolic footprint, genus composition, and interaction networks. Oxamyl and Furfural significantly reduced bacterial and fungal feeder populations. MWE had no impact on free-living nematode populations. Oxamyl and Furfural-treated soil samples were dominated by Rhabditis at 3DAA and Meloidogyne spp. at 34DAA. On the contrary, MWE-treated soil showed a balanced distribution, with Rhabditis, Panagrolaimus, Mesorhabditis, and Diploscapter being equally abundant. MWE treatment exhibited higher diversity indices (Shannon and Simpson) and equitability. Network analysis showed that the Oxamyl network had the highest fragmentation, while the MWE and Furfural networks had higher cohesion compared to the control. Mesorhabditis spp. in the MWE network played a crucial role, being directly connected to the omnivore genera Thonus and Aporcelaimellus. Our results indicated that continuous MWE application, besides controlling Meloidogyne spp., could enhance the structure and stability of the soil-free-living nematode community.