Studies on factors which educe watercore in Japanese pear (Pyrus pyrifolia Nakai cv. Hosui)

The interrelationships between the development of watercore, fruit maturity, and diur-nal temperature during July, and the use of plant growth regulators, ethephon and GA, were studied in the Japanese pear (Pyrus pyrifolia Nakai cv. Hosui). 1. When potted pear trees were transferred to a phytotron in July to expose them to 23°/15 °C (day/night), severe watercore symptoms developed in four out of five years, as compared to fruits on trees exposed to 33°/25 °C or field-grown potted trees (control). In these afflicted fruits, the flesh was more physiologically mature than was the skin. 2. There is a high degree of correlation between the development of watercore and the exposure of pear trees to relatively cool temperatures 80 to 100 days after full bloom. 3. The percentage of fruits displaying watercore increased with the advancement of fruit maturity ; fruit with large affected areas in their flesh had lower specific gravity and softer flesh. 4. Treatments with ethephon and gibberellic acid which accelerated maturity also fos-tered the development of large watercores.