Decrease of Leaf Water Potential and Leaf Injury of Tea Plant (Thea sinensis L.) Subject to Cold Winter Wind in Sanin Region of Japan

Tea leat sometimes receives serious damage as leaf blight or defoliation by winter cold wind in Sanin region of Japan. When wind of 4-7ms¹ blew, air temperature decreased to 0~–4.4-C and a little snow remained on the ground, leaf water potential (ΨL) of tea plant (cv. Yabukita) was lowered to −1.2MPa in mid night and decreased to –2.3MPa in daytime of the next day. Leaf blight appeared one or two days after the condition. This temperature is a little higher than that causing freeze damage of tea leaves. However, when wind speed was lower that, air temperature was near 3–5-C and there was no snow,ΨL decreased only to –1.0MPa and leaf injury was not observed.ΨL did not decrease under –1.1 MPa even in a hot summer day. We observed relationships between pressure rate and leaf injury of tea leaves pressurized with a pressure chamber in order to make analogous comparisons with decreases of Ψ by the cold winter wind. Leaf death started from pressurized rate l.OMPa and 1.8MPa in winter and summer tea leaves, respectively, and the death was urged by more increase of pressurization rate. We suggested that the cold wind injury is caused by water deficiency of tea leaf as indicated by decrease of tΨL under the strong cold wind and low temperature condition, and, in particular, winter tea leaves more easily receive damage because winter leaves are sensitive to decrease of ΨL more than other seasons leaves.