Metabolomic analysis of Chinese chestnut ( Castanea mollissima Bl.) leaves in response to Oligonychus ununguis feeding stress

Piercing-sucking insects such as the chestnut red mite (CRM; Oligonychus ununguis ) damage leaves by extracting mesophyll cell nutrients, thereby reducing photosynthesis and nut yield in Chinese chestnut ( Castanea mollissima Blume). However, the metabolic basis of the chestnut response to mite stress remains elusive. To address this, leaf metabolomics was conducted on four varieties with different resistance levels. Resistance grades were determined by the leaf chlorosis index, and three comparison groups were established. Secondary metabolome profiling revealed that resistant varieties showed greater metabolic changes under infestation than susceptible ones. In total, 713 total metabolites and 275 metabolites with significantly differential accumulation among germplasms were identified across the comparisons. KEGG enrichment highlighted 246 metabolites and 75 differential metabolites involved in flavonoid, flavonol, and phenylpropanoid biosynthesis. Notably, 27 phenylpropanoids and flavonoids accumulated significantly in resistant varieties but were largely absent or unchanged in susceptible ones. These findings suggest that specialized phenylpropanoids and flavonoids, along with their associated pathways, play key roles in CRM resistance, providing a foundation for breeding mite-resistant chestnut varieties.