Conditioning of Soil Nematode Communities by Preceding Plants Enhanced Crop Resistance Against Invasion by Root-Knot Nematodes

Plants and local soil microbiota self-organize as holobionts, thereby increasing resistance to pathogens. However, the local factors that contribute to self-organization are not well understood. We hypothesized that top-down control of the rhizobiome by local soil nematode communities could suppress pathogens, depending on how preceding plants condition the nematode community. In five pot experiments, we inoculated fallow soil microbiomes and conditioned nematode communities to tomato or potato seedlings growing in sterile sand, to test the resistance of the assembled holobionts to root-knot nematode invasion. Tomato resistance increased with nematode communities conditioned by tomato plants compared to oilseed rape or fallow soil, while inoculation of nematode communities alone, without a soil microbiome, did not decrease root invasion. In contrast, nematode communities conditioned by tagetes enhanced resistance compared to nematode communities from tomato without a soil microbiome. Nematodes from crotalaria decreased invasion of potato roots more than nematodes from black oat or fallow soil, especially with co-inoculation of a soil microbiome. Solely inoculating the microbiome conferred no resistance. In conclusion, soil nematodes play a role in the local self-organization of crop holobionts depending on the preceding plants. Crop rotation schemes may be used to fortify crops against soil-borne pathogens.