Phytochemical Diversity in Populus trichocarpa Buds: Insights into Population Variation and Antifungal Properties

Buds are a critical stage in the annual growth–dormancy cycle of perennial woody plants and are essential for survival and biomass accumulation. To safeguard these structures, trees employ both physical and chemical protection. Although Populus buds are known to contain rich phytochemistry, population-level variation remains largely unexplored. Here, we characterized bud phytochemistry across a population of Populus trichocarpa natural variants using gas chromatography–mass spectrometry and examined the antifungal properties of bud extracts. In the reference genotype Nisqually-1, a total of 32 lipophilic metabolites were detected, belonging to four chemical groups: terpenoids, phenylpropanoids, linear hydrocarbons, and others. Analysis of 49 additional P. trichocarpa natural variants revealed both shared features and substantial variation. All lines contained metabolites from the phenylpropanoid, linear hydrocarbon and terpenoid classes, which consistently dominated the profiles. However, quantitative differences in individual metabolites and relative class abundances distinguished the lines, allowing them to be grouped into three chemotypic clusters. To assess potential biological implications of phytochemical variance, we tested antifungal activity of bud extracts against the pathogenic fungus Fusarium oxysporum. Extracts from all 50 lines significantly inhibited fungal growth compared with controls. Correlation analyses between metabolite abundance and inhibition strength identified candidate metabolites that were most strongly associated with antifungal activity. Together, these findings reveal both conserved and variable components of bud phytochemistry in P. trichocarpa. The observed chemical diversity and consistent antifungal effects suggest that bud metabolites contribute to defense and may reflect adaptation across natural populations.