Neofusicoccum laricinum, 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 Evodia rutaecarpa var. rutaecarpa, 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.

Larch shoot blight, caused by Neofusicoccum laricinum, threatens global larch resources, while conventional chemical control is constrained by pollution and resistance. To address this gap, we integrated metabolomics, transcriptomics, and antifungal efficacy assays to identify Fraxetin, a disease-induced phytoalexin, and to elucidate its antifungal activity and mechanism. Metabolomics showed infection-triggered accumulation of Fraxetin in resistant Larix olgensis shoots. Antifungal experiments showed that within the range of 68–1088 μg/mL, the optimal antifungal concentration was 1088 μg/mL. When inoculated larches were treated with 1088 μg/mL Fraxetin, the maximum inhibition rate of pathogen growth reached 66.67% within 12 days, and the symptoms of the treated plants were alleviated. Transcriptomics revealed activation of damage responses, disruption of oxidative homeostasis, and compromised membrane integrity in the pathogen under Fraxetin treatment. Physiological measurements confirmed increased lipid peroxidation, redox collapse, membrane leakage, and reduced fungal viability. These findings indicate a lipid peroxidation–mediated oxidative–membrane mode of action and support the potential of plant-derived Fraxetin for more sustainable management of larch shoot blight.

Phenolic levels in Larix gmelinii are closely correlated with its interaction with Neofusicoccum laricinum. As a vital subclass of phenolics, phenolic acids participate in both constitutive and inducible plant defense responses. In the present study, metabolomic, transcriptomic, physiological and biochemical analyses were conducted to investigate the tissue heterogeneity of phenolic acid metabolism in larch stem tissues, as well as the dose-dependent effects and underlying mechanism of vanillic acid (VA) on N. laricinum, providing valuable insights into the interaction between L. gmelinii and N. laricinum. A total of 119 differentially accumulated phenolic acid metabolites were identified in this study. Shoots exhibited markedly higher levels of most phenolic acids, including VA, than trunks and branches, accompanied by significant enrichment of the phenylpropanoid biosynthesis pathway. Notably, VA exhibited a biphasic dose–response on N. laricinum, facilitating the growth of N. laricinum at low concentrations (2–1117.12 μg/mL) and exerting inhibitory effects at high concentrations (>1117.12 μg/mL). Transcriptomic analysis further suggested that phenolic acid metabolism and the overcompensation effect collectively accounted for this unique dose–response pattern. Collectively, this study verified that phenolic acid metabolism across L. gmelinii stem tissues presented distinct tissue heterogeneity, and VA exerted a biphasic dose–response on N. laricinum.