THE PHYSIOLOGICAL MECHANISM OF WATERCORE IN JAPANESE PEAR (PYRUS-PYRIFOLIA NAKAI VAR CULTA NAKAI) AND ITS PREVENTION BY CALCIUM EDTA

The occurrence, mechanism and methods to reduce of the frequency of the physiological disease, watercore, in the Japanese pear 'Hosui' were studied by applying calcium compounds, calcium binders, or calmodulin inhibitors as a paste on the pedicel or by spraying the fruit. 1. When calcium chloride, calcium acetate, calcium citrate, calcium gluconate and Calcium EDTA were applied as a paste on the pedicel, the frequency of watercore was reduced as compared with the untreated control fruits. Ca-EDTA was most effective. However, when the same chemicals were sprayed on the fruit, the treatments were ineffective. 2. When the fruits on a tree which regularly produced a high number of fruits with watercore were treated with Ca-EDTA paste, the treatment increased the ratio of healthy fruits fourfold and reduced the ratio of severe watercore fruits to about 60%. Furthermore, the occurrence of watercore caused by ethephon was much suppressed by an application of Ca-EDTA on the pedicel. Thus, the use of Ca-EDTA is recommended to reduce the prevalence of watercore in Japanese pears. 3. Spraying with trifluoperazine, a calmodulin inhibitor, on the fruit or applying it on the pedicel increased the occurrence of watercore. 4. Calcium content in fruit treated with Ca-EDTA paste was higher in alcohol soluble fraction as compared with the other treatments and control. However, the calcium content in the buffer and salt soluble fractions of the fruit treated with Ca-EDTA paste was the lowest. These results suggest that the changes in the distribution of calcium in fruit cells are related to the occurrence of watercore.