Plant Shoot Age and Temperature Effects on Essential Oil Yield and Oil Composition of Rose-Scented Geranium (Pelargonium sp.) Grown in South Africa

摘要

A field experiment was conducted during 2005/2006 at the Experimental Farm of the University of Pretoria, South Africa to investigate the changes in herbage yield, oil yield and the variation in the concentration of the major components of rose-scented geranium. The essential oil was isolated by steam-distillation and the composition was determined by gas chromatography (GC). The results revealed that herbage yield increased over time in the first four (autumn/winter) and five (spring/summer) months of the respective harvesting cycles. The plants harvested in the spring/summer cycle had higher herbage yield and oil percentage than plants harvested in the autumn/winter cycle. The decrease in oil percentage was associated with low night temperatures in the autumn/winter cycle. The geraniol content decreased with decreasing night temperatures in autumn/winter while the citronellol content showed a tendency to increase. Geraniol followed a similar trend when regressed against plant shoot age in both experimental cycles. The decrease in geraniol content with respect to plant shoot age, therefore, increased the citronellol: geraniol ratio in both experimental cycles. The spring/summer harvesting season was superior to the autumn/winter season in all commercial aspects of rose-scented geranium oil production.