Study on the immune defense response of Epimedium sagittatum induced by Colletotrichum fructicola and its biological control

In agricultural production, Epimedium sagittatum fuels traditional Chinese health products but loses much economic value to anthracnose ( Colletotrichum fructicola ). This study evaluated yield and quality losses, detected C. fructicola colonization via qPCR, analyzed E. sagittatum ’s immune response, and screened endophytic biocontrol bacteria. Results showed C. fructicola HY3–2 caused 7.62 % yield loss and 72.79 % reduction in total content of six bioactive components (p < 0.01), detectable at 8 h post-inoculation with lesions at 72 h. Infection activated reactive oxygen species (ROS) scavenging, upregulated flavonoid biosynthesis genes (e.g., EsC4H , EsDFR2 ), and induced icariside I, icariside II accumulation, which inhibited C. fructicola HY3–2 by disrupting its mycelial cell membrane. Bacillus velezensis SY-22 exhibited strong field biocontrol efficacy (therapeutic 54.15 % > preventive 30.57 %). Genome analysis identified 13 secondary metabolite biosynthetic gene clusters, with fengycin and surfactin confirmed as inhibitory metabolites. This study first identifies icariside I and icariside II as phytoalexins, providing insights into E. sagittatum ’s immune mechanisms and guiding anthracnose biocontrol for its standardized production. • Colletotrichum fructicola significantly reduces flavonoids in Epimedium sagittatum. • Icariside I and icariside II were first identified as phytoalexins. • Bacillus velezensis SY-22 exhibits strong biocontrol ability against anthracnose. • Bacillus velezensis SY-22 exerts biocontrol via secreting fengycin, surfactin, etc.