From Resistance Mechanism to Green Application: Discovery of Rutaevin as a Key Phytoalexin in Larch and Cross-Species Resource Optimization

<i>Neofusicoccum laricinum</i>, the pathogen responsible for larch shoot blight, is a hemibiotrophic pathogen. A hypersensitive reaction of plants does not inhibit the growth of the pathogen, while phytoalexin is an antifungal compound secreted by plants, which can directly destroy the cells of pathogens and help plants achieve resistance. This study aimed to investigate the chemical defense mechanisms in resistant larch, identify key biocontrol agents, and assess their potential for field application. By integrating multi-omics technologies with time-dependent models and dose-response curve analysis, the accumulation and antimicrobial properties of rutaevin were examined. Its application potential was verified through cross-species resource screening and field trials. The results revealed that rutaevin acts as a phytoalexin against larch shoot blight. It began to accumulate linearly 0.62 days after pathogen exposure, with its antifungal activity demonstrating a dose-dependent response, achieving 100% inhibition at 0.5 mg/mL. The activation of terpene metabolic pathways in disease-resistant plants resulted in a significant increase in rutaevin content compared to susceptible plants. Cross-species screening showed that the highest concentration of this compound is found in the fruit of <i>Evodia rutaecarpa</i> var. <i>rutaecarpa</i>, with its crude extract exhibiting strong field efficacy. The findings provide theoretical and technical support for disease-resistant breeding and the development of plant-derived fungicides.