Physiological studies on the cold resistance of the tea plant

Abstract

For the purpose of investigating the physiological properties of the tea plant with regards to the cold resistance, the experiments were carried out from November in 1952 to March in 1953, using two triploid and 6 diploid varieties. Autumn branches of each variety were gathered every 10 days for 4 months from November and they were kept under the constant temperature regulated to -5°C, -10°C and -15°C by the electric refrigerator for 30, 60 and 120 minutes respectively. After the treatment cold injuries of leaves were observed. Simultaneously the content of water and reducing sugar of leaves, and refractive index of leaf-juice were investigated. Resistance of the plant to low temperature gradually increased from November and reached maximum in the beginning of February. Then toward the end of February it decreased again and in March it decreased rapidly. As regards the varietal difference, it was found that the resistance of each variety to low temperature treatment was proportional to winter hardiness in the field. The varieties such as Makinohara-wase and U-21, which were hardiest in the field, showed the strongest resistance in the refrigerator, and in the beginning of February they began to be injured by more than 120 minutes exposure to -15°C, while diploid varieties began to be injured by 30 minutes exposure to -15°C. In March, however, all the varieties decreased cold resistance. The content of reduing sugar and the refractive index began to increase from November in parallel to the cold resistance, reached maximum in the beginning of February, while water content decreased and reached minimum in February, in the beginning of February the resistant varieties show higher content of reduing sugar, greater refractive index and than lower content of water the less resistant varieties. In March all the varieties were inclined to decrease in reducing sugar and refractive index, and increase in water content in leaves. Then varietal difference was hardly recognized at that time.