Nitrogen availability shapes anthracnose severity and defense-related responses in chili pepper (Capsicum annuum)

Fungal 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. High nitrogen supply increased disease severity in chili pepper infected with Colletotrichum fructicola.Nitrate accumulation in lower leaves positively correlated with lesion expansion.Pigment levels (chlorophyll, β-carotene, flavonoids, anthocyanins) were regulated mainly by nitrogen status rather than infection.Gene Ontology analysis identified ‘response to nitrogen compound,’ ‘response to stress,’ and ‘hormone signaling’ as conserved fungal response pathways.Low nitrogen levels were associated with enhanced induction of selected defense-related genes, such as WRKY25 and TT8. High nitrogen supply increased disease severity in chili pepper infected with Colletotrichum fructicola. Nitrate accumulation in lower leaves positively correlated with lesion expansion. Pigment levels (chlorophyll, β-carotene, flavonoids, anthocyanins) were regulated mainly by nitrogen status rather than infection. Gene Ontology analysis identified ‘response to nitrogen compound,’ ‘response to stress,’ and ‘hormone signaling’ as conserved fungal response pathways. Low nitrogen levels were associated with enhanced induction of selected defense-related genes, such as WRKY25 and TT8.