Contribution of soil free-living nematode communities to suppression of Meloidogyne incognita in organic fields

Predatory and omnivorous nematodes are known as potential biological control agents for root- knot nematodes (RKN). However, it is still unclear whether free-living nematodes (FLN) communities, including microbial-feeding nematodes, contribute to RKN suppression. To evaluate their contribution, a pot experiment was conducted using soils containing either 1) microbes or 2) microbes and FLN. After six weeks of green pepper growth, we analysed the level of Meloidogyne incognita infection and the bacterial community with next-generation sequencing (NGS). The same analysis was conducted after an additional 1-month incubation. Meloidogyne incognita densities were significantly lower in soils with FLN than in those with microbes only. Moreover, M. incognita multiplication was suppressed even in the absence of predators and omnivores, highlighting the importance of microbial-feeding nematodes. NGS results showed that some bacterial genera had a significant negative correlation with M. incognita density, suggesting that bacterivores altered bacterial communities to promote microbial suppression of M. incognita.