The Effect of Temperature on Growth, Oil Yield and Oil Quality of Japanese Mint

Abstract

Field studies of factors affecting yield and composition of Japanese mint oil are confounded by interacting environmental agencies. The effect of temperature, separated from other influences, was examined on Japanese mint (Mentha arvensis L. var. piperascens Holmes) in the naturally lit controlled environment Phytotron, Canberra, Australia. The So Wo I variety of Japanese mint was grown under 12 treatments consisting of four day and three night temperatures. Maximum leaf, stem and root dry matter was produced under 30 °C day temperatures, regardless of night temperature, but maximum stolon growth occurred at 20 °C temperatures. Generally, oil yield could be estimated by determining dry matter of above ground parts, but number of oil glands on the leaves did not provide a reliable indication of oil yield. Different temperature treatments did not appear to affect greatly the percentage of menthol, an important component of the oil. Under field conditions, maximum yield of Japanese mint oil has been found to occur during flowering. This close relationship between oil yield and flowering did not occur under extremes of temperature. Although 30 °C was found to be the optimum day temperature for oil yield in this experiment where only one harvest was made, it is possible that where multiple harvests are conducted, a lower optimum temperature might be found, since the higher temperature was detrimental to dry matter reserves in the stolons.