Effect of Leaf Age on Essential Oil Yield and Composition in Rose-scented Geranium

Abstract

Knowledge of essential oil content and composition of leaves of different ages could be used as a guide for the right herbage harvesting stage in rose-scented geranium. Change in essential oil yield and composition with leaf age in rose-scented geranium was investigated in a glasshouse of the University of Fort Hare, during the 2012 and 2014 crop seasons. The topmost five pair of leaves on shoots were separately harvested as treatments. Leaf fresh and dry mass were significantly lower in the topmost and the oldest leaf pair. Essential oil in the topmost pair was colorless; but with advance in leaf age, the oil tended to have a blue-green color. Oil content (on a dry mass basis) from the topmost to the bottom most were about 7.0%, 4.9%, 3.2%, 2.4%, and 1.9%, respectively. Oil yield was consistently the highest in the second youngest pair of leaves, and it progressively declined with leaf age. Contributions of the five leaf pairs from the topmost to the bottom most, in respective order, to the total yield were 19.3%, 22.0%, 17.71%, 12.03%, and 8.5%. The citronellol:geraniol ratio was lower in the young leaves than in the old leaves. Linalool and geranyl formate concentrations were the highest in the youngest leaves, and the opposite was true of isomenthone. The current results indicate shorter regrowth cycles would increase essential oil yield and quality of rose-scented geranium, provided an efficient harvesting technique was innovated.