Abstract
Fennel (Foeniculum vulgare Mill.) is an aromatic herb cultivated worldwide. Narrow-wavelength red LED light can potentially regulate the accumulation of secondary metabolites such as aroma compounds, but its impact on fennel aroma remains unclear. This study investigated supplemental red LED effects on fennel aroma using nutrient film hydroponic systems, comparing natural greenhouse light (control) with supplemental red LED (100 μmol·m-2·s-1, 14 h·d-1). GC-MS-O characterized aroma compounds in fresh fennel while RNA-seq analyzed gene expression. Supplemental red LED was found to enhance fennel growth and significantly increase aroma-active compounds in leaves, particularly phenylpropanoids like (E)-anethole and estragole. RNA-seq revealed 1958 upregulated and 278 downregulated genes. Phenylpropanoid biosynthesis genes such as eugenol synthase and isoeugenol synthase were upregulated. These gene-metabolite associations are correlational and functional validation was for future studies. Results demonstrated the potential application of LED lighting for enhancing culinary herb quality in controlled environments and provided molecular insights for fennel aroma biosynthesis.