Microbial communities and high trophic level nematodes in protected argan soil show strong suppressive effect against Meloidogyne spp.

Abstract

In many agroecosystems, soil suppressiveness to root knot nematodes (RKN) is of great interest in defining the biological agents controlling population density, especially with growing concerns about the environmental and human health impacts of chemicals. In this study, we evaluated the suppressiveness to spp. in two land use soils: a protected argan soil from the Souss Massa National Park (SMNP), Morocco, and a conventional soil from an adjacent non-protected area. Using next-generation sequencing (NGS) technology, we characterized the fungal and bacterial communities in these soils for the first time. Nematodes belonging to different trophic guilds were also analyzed to further understand ecological factors that enable suppressive organisms to function and persist in the soil. The experiment was conducted in a greenhouse with tomato plants grown in untreated and autoclaved soils, each inoculated with 800 infective juveniles (J2). We found that omnivore-predator nematode abundance, structure, and maturity indices were higher in the protected soil indicating the presence of a well-structured soil food web and a stable ecosystem. After sixty-seven days, RKN population density and gall index were reduced by 79.6 % and 81.5 % in the protected soil, respectively. 50 % autoclaved protected soil was also suppressive, but not 75 % and totally autoclaved soil. In contrast, conventional soil amplified the RKN population by 1319 %. More than 6770 bacterial and 558 fungal taxa were detected in this study, with Firmicutes, Actinobacteria, Mortierellales, Orbiliales, Agaricales, Diversisporales, and Pleosporales being consistently associated with RKN suppression. We found that fungal diversity was higher in SMNP-protected soil. In conclusion, soil protection enhances soil ecosystem resilience and that protected argan soils can serve as a valuable source of biological agents for the sustainable management of phytoparasitic nematodes.