Nitrate supply increases the resistance of cucumber to Fusarium wilt disease by regulating root exudation

Yield losses caused by Fusarium wilt pose a risk to global food security. Nitrogen fertilizer regime affected the soil bacterial community and could reduce the occurrence of diseases. However, there are unresolved questions regarding the effects of single or combined applications of different nitrogen forms on disease development. Here, using the split-root system, we explored the impact of two forms of nitrogen (nitrate and ammonium) on the cucumber’s resistance to Fusarium. We found that nitrate supply altered the rhizosphere bacterial taxa, which could inhibit the Fusarium. Moreover, metabolomic analysis demonstrated that rhizosphere bacterial taxa gradients along the lateral distance from the root are associated with the release of root exudates. Our research revealed that ammonium-induced root exudates included several compounds, specifically gluconic acid, sorbitol, and sorbose, which were shown to be preferred by pathogen. These metabolites might negatively affect the growth of beneficial bacterial taxa. We found that nitrate enhanced the release of root exudates, such as guanidinosuccinic acid and behenic acid, that inhibited pathogen growth and recruited beneficial bacterial taxa. In summary, our results highlighted that nitrate supply can shape the spatial patterns of the rhizosphere microbial community by regulating the composition of root exudates to inhibit the growth of the pathogen, thereby reducing disease occurrence. This study provides a novel insight into how nitrogen forms affect rhizosphere microbial assembly to promote plant health.