Cucumber Fusarium wilt, induced by
Fusarium oxysporum f. sp.
cucumerinum (FOC), causes severe losses in cucumber yield and quality. Nitrogen (N), as the most important mineral nutrient for plants, plays a critical role in plant–pathogen interactions. Hydroponic assays were conducted to investigate the
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Cucumber Fusarium wilt, induced by
Fusarium oxysporum f. sp.
cucumerinum (FOC), causes severe losses in cucumber yield and quality. Nitrogen (N), as the most important mineral nutrient for plants, plays a critical role in plant–pathogen interactions. Hydroponic assays were conducted to investigate the effects of different N forms (NH
4+ vs. NO
3‒) and supply levels (low, 1 mM; high, 5 mM) on cucumber Fusarium wilt. The NO
3‒-fed cucumber plants were more tolerant to Fusarium wilt compared with NH
4+-fed plants, and accompanied by lower leaf temperature after FOC infection. The disease index decreased as the NO
3‒ supply increased but increased with the NH
4+ level supplied. Although the FOC grew better under high NO
3− in vitro, FOC colonization and fusaric acid (FA) production decreased in cucumber plants under high NO
3− supply, associated with lower leaf membrane injury. There was a positive correlation between the FA content and the FOC number or relative membrane injury. After the exogenous application of FA, less FA accumulated in the leaves under NO
3− feeding, accompanied with a lower leaf membrane injury. In conclusion, higher NO
3− supply protected cucumber plants against Fusarium wilt by suppressing FOC colonization and FA production in plants, and increasing the plant tolerance to FA.
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