Abstract:

Using two-year-old Rosa rugosa‘Fenghua’plants，we investigated the effects of foliar-applied melatonin（0.1，0.3 and 0.5 mmol · L^-1）on floral volatile organic compound（VOC）emission. Treatment with 0.3 or 0.5 mmol · L^-1 melatonin significantly increased flower diameter by 21.3% and 22.2%，respectively. Application of 0.3 mmol · L^-1 melatonin markedly enhanced the contents of key aroma compounds：at the bud stage，geraniol，citronellol，and methyleugenol increased by 100.0%，39.1% and 52.2%，respectively；at full bloom，citronellol and the monoterpene esters citronellyl acetate and geranyl acetate rose by 50.7%，102.2% and 108.2%，respectively. Concurrently，2-phenylethanol and its derivative phenylethyl acetate increased by 71.9% and 164.8%. These results indicated a nonlinear dose-response relationship，where VOC levels peaked at 0.3 mmol · L^-1 melatonin and declined at higher concentrations. qRT-PCR analysis showed that 0.3 mmol · L^-1 melatonin significantly upregulated four terpenoid biosynthesis-related genes and the key 2-phenylethanol synthesis gene RrAADC（aromatic amino acid decarboxylase）. Virus-induced gene silencing（VIGS）of RrAADC confirmed its central role：melatonin application in silenced petals restored both RrAADC expression and 2-phenylethanol accumulation to wild-type levels，demonstrating that RrAADC is a critical target gene in melatonin-mediated regulation of 2-phenylethanol biosynthesis.

Key words: rose, melatonin, volatile organic compounds, terpenoids, 2-phenylethanol, RrAADC