478 Characteristics of Fruit Flesh Pithiness Symptoms in `Yumyeong' Peach [Prunus persica (L.) Batsch]

`Yumyeong' peach has the desirable characteristics of long shelf-life and specific non-melting nature with a long harvest period. However, some fruits harvested too late show fruit pithiness symptoms or internal breakdown. This study was conducted to analyze the differences between fruit flesh pithiness and internal breakdown symptoms and to find out the source of flesh pithiness in `Yumyeong' peach. The rate of flesh pithiness was higher in fruit harvested late in the season. Sugar and malic acid contents showed no differences between the normal and flesh pithiness fruits, but the acidity was significantly lower and was affected by low citric acid content in flesh pithiness fruit. In flesh pithiness fruits, calcium contents were low both in skin and flesh. Occurrence of flesh pithiness fruits was high in the years with low precipitation and high temperature for 2 months before harvest. In observations on morphological characteristics, the parts showing flesh pithiness consisted of smaller cells than the normal parts. Tonoplasts disintegrated and the number of dead cells was high in internal breakdown fruits, while the tonoplasts were intact, with contracted vacuoles, in flesh pithiness fruits. Tylosises were observed in vascular tissues around the flesh pithiness; therefore, it was assumed that those tylosises restrict flesh tissue development, resulting in flesh pithiness. Other varieties (`Fantasia', `Wolmi' and `Hakuto') also showed tylosis, and smaller cells were observed in the flesh tissue of these cultivars, indicating abnormal growth of the flesh part. These results suggest the possibility of the occurrence of pithiness-like symptoms in other peach varieties.