Comparative physiological and defense strategies of Ardisia crispa (Thunb.) A. DC. against Annulohypoxylon stygium and Diaporthe angelicae with screening of antagonistic endophytes

Ardisia crispa (Thunb.) A. DC. (A. crispa), a valuable medicinal plant, is severely affected by fungal pathogens, yet its defense mechanisms against such infections remain poorly understood. In this study, we conducted a comparative investigation of the physiological and molecular responses of A. crispa to infections by two pathogenic fungi with distinct ecological origins, namely Annulohypoxylon stygium (A. stygium, a saprophyte-derived opportunistic pathogen) and Diaporthe angelicae (D. angelicae, a specialist plant pathogen). The results revealed that A. stygium induces strong oxidative stress, significantly suppressing the activities of antioxidant enzymes and causing severe damage to cell membranes, chloroplasts, and mitochondria. In contrast, D. angelicae primarily reduced chlorophyll content and triggered a delayed physiological response. Transcriptomic analysis demonstrated that A. crispa defends against A. stygium by upregulating LOX2S, AVP, and ALDO to exacerbate membrane damage, while simultaneously activating DNAJA2 and CAT to mount antioxidant and osmoregulatory responses. In contrast, against D. angelicae, it suppresses photosynthetic genes, coordinates the expression of key genes such as LOX2S and GCPE, and maintains flavonoid biosynthesis to support an adaptation based on chemical defense. Moreover, from 703 endophytic fungal isolates obtained from Ardisia crenata Sims, we identified Diaporthe sp. and Neofusicoccum parvum as highly effective antagonistic strains, with relative inhibition rates of 88.95 % and 91.49 % against A. stygium and D. angelicae, respectively. This study provides the first comparative analysis of infection strategies and host defense mechanisms against these two pathogens in A. crispa, and identifies promising antagonistic endophytes for developing biocontrol strategies in medicinal crop protection.