Boonyaves K.Sanghirun J.Suwitchayanon P.Supaibulwatana K.Mahidol University2026-02-062026-02-062026-01-01Journal of Plant Interactions Vol.21 No.1 (2026)17429145https://repository.li.mahidol.ac.th/handle/123456789/114526Fungal diseases threaten global food security, causing up to 40% yield losses. Nitrogen availability shapes plant immunity, yet the detailed morphological, physiological, and molecular understanding of its role in plant–pathogen interactions remains limited. We examined chili pepper infected with Colletotrichum fructicola under varying nitrogen supplies. Disease severity increased with higher nitrogen, with the largest lesions observed at 30 mM, while pigment levels were nitrogen-dependent. Lower leaves accumulated more nitrate, correlating with greater lesion expansion. Analysis of publicly available Arabidopsis datasets identified response to nitrogen compound, stress, and hormone signaling as conserved fungal responses. In chili pepper, expression analysis of selected genes involved in nitrogen metabolism, hormone signaling, and stress responses revealed induction of most genes, including WRKY25 and TT8, under low nitrogen upon infection. These findings suggest that nitrogen status is associated with changes in defense-related responses, highlighting nitrogen management as a potential factor influencing crop resilience to fungal pathogens.Agricultural and Biological SciencesArticleSCOPUS10.1080/17429145.2025.26115032-s2.0-10502702571217429153