Citronellol: geraniol ratios and temperature in geranium (Pelargonium hybrid)

Concentrations of citronellol and geraniol in essential oil from rose geran ium (Pelargonium hybrid) were monitored monthly over four years using gas c hromatography-mass spectrometry. Geraniol concentrations fell in winter and citronellol concentrations increased in spring. The citronellol/geraniol ( C:G) ratio was a more sensitive indicator of change in oil composition than the concentration of either alcohol in isolation. C:G ratios rose sharply if the minimum air temperature (T-min) fell below 5.5 degrees C for any tim e during the 5 d prior to monthly harvesting, A nonlinear model is proposed to predict the C:G ratio at any T-min. High C:G ratios indicated cold stre ss in geranium plants.