A simple diagnosis and incidence prediction of the pithy fruit in Japanese pear (Pyrus pyrifolia Nakai cv. Niitaka) using specific gravity

The pithiness called 'suiri' in Japanese pear fruit is one of the most serious physiological disorders that deteriorates flesh texture. A simple diagnosis of the pithy fruit using specific gravity and an incidence prediction method of pithiness was devised. The symptom arose when the specific gravity of the fruit dropped under 0.95 and the degree of pithiness increased with the further decrease of the specific gravity. The specific gravity could be estimated by the ratio of the fruit diameter and floated portion, when it was placed in water. The mean error between estimated and measured value was 0.007, making it suitable for practical use. There was a positive correlation between specific gravity 2 weeks before harvest and that of the peak of harvest. Since the specific gravity drops to under 0.95 at harvesting, if it is under 0.98 two weeks before harvest, it is necessary to harvest earlier, to achieve best fruit quality.