Abstract
1. The bark splitting injury has frequently occurred in various parts of warm region in recent years. A wide range of resistance to the bark splitting injury under the field conditions also has been observed among the tea clones.
The resistance of the clonal varieties was ranked by means of both the observations of the injury at the various sites of Kyushu district and the results obtained by the newly developed testing methods.
The ranking of the hardiness among the main clones was shown as follows : Kanayamidori> Yabuki to>Asatsuyu>Sayamamidori>Okumusashi, Yaeho (hardy>tender).
2. It was cleared that the resistance to the injury did not correlate with the frost hardiness of mature leaves in mid-winter which closely influences northern limits of commercial cultivation of tea plants, the time of bud opening, the vigor of plants and the quality of green tea.
3. The following three testing methods for the bark splitting injury were proved to be effective : 1) testing for the frost hardiness of the basal stem of young plants at the period of the first autumn frost, 2) testing for the easiness of artificial occurrence of the bark splitting induced by the repeated freezing treatment and 3) testing for both the frost hardiness and the cambial activity of the mature shoot of adult plants.
The cambial activity was estimated by easiness of peeling the stem bark from the sapwood and by water content of stem.
The last method is simple and easy to be applied to the actual breeding procedure.
4. The best period for the testing of resistance to the bark splitting injury is confirmed to be late October to the end of November at Tea Branch of Miyazaki Agricultural Experimeut Station.
