The accumulation and composition of essential oil in kumquat peel

Essential oils are important secondary metabolites, which are mostly synthesized and accumulated in secretory cavities. In this study, the accumulation of essential oil, variation in composition and the pattern of expression of genes related to monoterpene biosynthesis during fruit development were investigated in kumquat peel. The number of cavities per fruit was approximately 2500. The average volumes of cavities were 16.05, 23.13, 32.69, 68.80 and 94.71 nL at 30, 60, 90, 120 and 150 days after flowering (DAF), respectively. During the fruit development, the average volume of the cavities in the peel increased consistently, and the accumulation of essential oil fit a sigmoid curve pattern. Limonene was the most abundant component (67.47–72.98%), followed by myrcene (3.91–4.83%), germacrene-D (1.86–3.00%), linalool (0.48–2.64%) and γ-elemene (1.79–2.12%). The content of compounds associated with disease resistance and pungent odor were reduced (or even disappeared) during fruit ripening. A correlation analysis showed that the expression of DXS2, HDR and IDI were closely related to the accumulation of essential oil in kumquat peel.