Seasonal Variation of both the Percentage Yield of Essential Oil and the Chemical Composition in Pelargonium species

[摘要] Pelargonium denticulatum had been the most popular of all Pelargonium species in Japan, but in 1954 three types of P. roseum, viz., varieties "Italy", "France" and "America", were introduced into Japan in the hope of obtaining better and more oil. P. roseum plants are more spreading and shrubby with vigorous growth than P. denticulatum, but the former is lower in yearly yield of oil per hectar. However, the oil of P. denticulatum is inferior to P. roseum in quality. B1 No. 10 was newly grown by the back cross of P. roseum "France" and P. denticulatum. In the oil yield rate, B1 No. 10 showed an intermediate value between P. roseum and P. denticulatum higher than P. roseum by 20-50 per cent, and also maintained a quite high oil yield in spring and late autumn seasons. Concerning the quality of extracted oil, B1 No. 10 was not inferior to P. roseum. The main components of the oil being citronellol and geraniol, the components existed generally in a free state. As a result of examining in the variation of citronellol and geraniol by gaschromatography, it was found that there was seasonal variation. That is, when the oil contents of them both in early period of growth were compared, the percentage of geraniol showed a higher value, but as the temperature got higher in summer the percentage of geraniol decreased, and on the other hand the percentage of citronellol significantly increased. However, as the temperature got lower in the months of November and December, the percentage of citronellol decreased and that of gernaniol again increased. The optical rotation of essential oil was also high in the season of high temperature and low in the season of low temperature. This is probably due to the increase and decrease in percentage of 1-citronellol. We can conclude that the seasonal variation of the percentage of citronellol and geraniol is due to a biochemical oxidation-reduction reaction. It is considered that geraniol is changed into citronellol mainly by phytochemical reduction during summer season, and that the percentage of geraniol is increased by dehydrogenation in late autumn season. The quality of geranium oil greatly depends upon the proportion of content of geraniol and citronellol. It has been reported that the above mentioned proportion is defferent according to the producing land and species, but as described above, the phenomenon that the oil content percentage is significantly different in different seasons of oil extraction can not be overlooked.

[学科分类] 农业科学（综合）