Occurrence of Bark Split Frost Injury due to Water Supply through Cracks on the Bark of the Tea Plant

Abstract

The bark split frost injury in tea plants is considered to occur as follows. A trunk freezes under the night sub-freezing conditions, and ice is formed in the cambium. Water absorbed from roots is supplied there, and as a result, the ice is enlarged, and a bark split occurs. In this study, we clarified a new water supply path other than the water absorption from roots.

First, we examined the origin of the liquid that leaked from the branch that we placed under the sub-freezing conditions. We assumed that it was the sap that leaked from the inside of the branch because the leaked liquid included theanine and sucrose based on the results of ingredient analysis of the leakage liquids. Furthermore, when we observed the liquid leakage point of the bark of the branch with a stereoscopic microscope, we observed an extremely small crack on the bark. We then examined the water supply path to the ice in the cambium under the night low temperature conditions. We could confirm only minimal water absorption and transpiration of the nursery stock under the 5 ℃ - dark condition, and the water absorption from roots was insufficient for a bark split. On the other hand, when we put a branch in rock wool containing the acid fuchsin solution under the sub-freezing conditions, the acid fuchsin solution penetrated only the part where the bark split of the branch had occurred. These results show that the water supply to the ice in the cambium, which causes bark split, occurs through extremely small cracks on the bark under sub-freezing conditions.