Alternative N-forms cause differential response to the soil-borne disease Fusarium oxysporum f. sp. melongenae in eggplant (Solanum melongena L.)

Mineral nutrition may strongly influence plant resistance or susceptibility to disease onset and progression, affecting plant growth and crop yield. Nitrogen (N) affects the plant-microbe interaction by modulating the production of antimicrobial compounds or defense-related enzymes and proteins that can boost or alleviate disease development.A comparative analysis of alternative N-forms (NO3- and NH4+) was conducted on the tolerant eggplant line AM199 during infection by Fusarium oxysporum f. sp. melongenae (Fom), a soil-borne pathogen. At 14 Days After Inoculation (DAI), NO3--fed plants exhibited significantly reduced disease symptoms and incidence over time compared to NH4+-fed plants, which showed more evident symptoms. Root transcriptomic comparative analysis elucidated the AM199 defence mechanisms at the early stage of Fom-infection (4 h after inoculation; T1) and the cross-talk between plant responses to the pathogen and the alternative N-forms supplied at long-term (14 days after Fom-inoculation; T2).At T1, we detected a rapid activation of genes involved in early defense, such as chitinases, proteinase inhibitors, cytochrome P450s, and receptor kinases, many of which mediate hypersensitive response and salicylic acid signaling. Furthermore, the plant pathogen recognition complex (LYK), involved in plant-pathogens interactions, was highly upregulated following inoculation. This activation, along with the induction of an Arabinogalactan protein (AGP) and an Aspartic protease (AP), which are involved in cell-to-cell communication signaling, as well as the enhancement of pathogen-associated molecular patterns (PAMP), contributed to an immediate response to Fom infection. In NO3--fed plants, the initial response to pathogen infection was followed by a stronger defense reaction compared to NH4+-fed plants. This was marked by higher expression levels of genes associated with Reactive Oxygen Species (ROS) and Resistance (R) responses, as well as the upregulation of genes involved in cell wall development, including cellulose biosynthesis (CSLG1, CSLH1) and membrane sterol production (SQE2), suggesting a potential thickening of the cell wall to hinder fungal invasion.Our study provides new valuable insights into the molecular mechanisms induced by Fom infection under alternative N-forms supply, contributing to the identification of improved fertilization strategies for disease management in eggplant, in support of more sustainable and low-impact agriculture.