Differential Susceptibility and HR-Like Resistance Responses in Arabidopsis thaliana to Colletotrichum coccodes and Colletotrichum scovillei.

Hemibiotrophic fungi of the genus Colletotrichum provide valuable systems for studying plant immunity and pathogen lifestyle transitions; however, compatible and incompatible interactions have rarely been compared within the same host species. Here, we show that Arabidopsis thaliana exhibits contrasting responses to two phylogenetically distinct hemibiotrophic fungi, Colletotrichum coccodes KACC40803 and Colletotrichum scovillei KC05. Multilocus phylogenetic analyses using ITS, ACT, GAPDH, and TUB2 sequences confirmed their taxonomic identities. The two fungi also differed morphologically, particularly in colony characteristics and appressorial structures. Inoculation of Arabidopsis leaves with Colletotrichum coccodes caused progressive chlorosis, necrotic lesions, extensive fungal colonization, acervulus formation, and increasing fungal biomass, indicating a compatible susceptible interaction. Host defense-related genes associated with salicylic acid- and jasmonic acid-mediated pathways were suppressed during infection. By contrast, Colletotrichum scovillei induced restricted lesion development, rapid accumulation of callose and reactive oxygen species, localized plasma membrane disruption, and strong induction of defense-related genes in Arabidopsis leaves, consistent with an incompatible hypersensitive response (HR)-like cell death. Fungal biomass remained low throughout infection, demonstrating effective restriction of colonization. Together, these findings establish a dual Arabidopsis-Colletotrichum pathosystem that enables comparative analysis of susceptibility and HR-like resistance within a single host, providing a tractable model for dissecting host specificity, immune signaling, and regulated cell death during hemibiotrophic infection.