Leaf Injury Caused by Drop in Leaf Temperature of Saintpaulia ionantha

Abstract

The relationship between leaf temperature before watering and the water temperature which causes leaf injury was examined by dipping the excised leaves of African violet, Saintpaulia ionantha Wendl. cv. ‘Beth Elen’ in water kept at constant temperature.
1. When the leaves kept at 30°C for 24 hr were dipped in 15°C water for 30 sec, the degree of injury of the outer leaves was greater than that of the inner leaves.
2. Leaves kept at 20°, 25° and 30°C for 24 hr were dipped in water of 5°, 10°, 15°, 20°, 25° and 30°C for 30sec. Leaf injury was caused by dipping the leaves in water kept at a 5°_??_10°C lower than the leaf temperature. Furthermore the degree of injury became severe with increasing difference between the leaf temperature and the water temperature.
3. When the leaves kept at 30°C for 24 hr were dipped in 15°C water for 1, 15, 30, 45 and 60sec, injury resulted even by dipping for 1sec, due to the rapid drop in leaf temperature.
4. Leaf temperature was decreased gradually from 30°C to 15°C in 5°C steps by dipping in water for a short time. It was found that leaf injury resulted from a dipping time of 15sec, but not of 30sec or longer.