Characteristic fruit development in 'Shimizuhakuto' peach in relation to physiological fruit drop [Japanese]

摘要

The possible causes of physiological fruit abscission (June drop) in peach (Prunus persica), which occurs between late Stage 2 and early Stage 3, was investigated for two years. The characteristics of fruit development in 'Shimizuhakuto (SH)' which has a high frequency of pit splitting and physiological fruit drop were compared with those in 'Takeihakuho (TH)' and 'Megohime (MH)' which tend to have numerous split pits but low fruit drop and with 'Yamatohakuto (YH)' which manifest a few split pits acid a small percentage of fruit drop. SH had a lower percentage of fruit drop than YH but its growth rate during Stage 1 was Easter than that of YH. The pits of SH and TH, based on fresh weight and size, grew significantly faster than those of YH throughout the entire developmental period. Seeds of SH elongated faster than those of YH but the former accumulated dry matter slower than did those of the latter after the middle of Stage 2. There was no difference in the dry matter accumulation of the pits between two cultivars. Throughout Stages 2 and 3, the length and cell diameters of embryos were smaller in the fruits of SH than in those of YH. In the former, the sizes of pits and embryos in the split-pit fruits were significantly larger than those in fruits with intact pits. The percentage of dry matter in seeds of split-pit fruits in SH varied widely, but at the heavier end on the distribution, the dry weights were similar in all fruits. Embryo lengths from SH fruits with split-pit was classified into normal and short categories, indicating that some seeds developed normally until pit-splitting stage. Seed weight and the sizes of endosperm and embryo in SH fruit which abscised were significantly smaller compared with those of normal ones, but the weight and size of pits were similar. When fruits of SH trees were thinned to two crop levels, heavy thinning resulted in larger fruits but with a higher percentage of split pits with small embryos and more fruit drop than lightly thinned tree. The high percentage of poorly developed embryos that existed in June drop fruits regardless of thinning level, suggests that inferior seed development prior to pit-splitting is related to June drop in SH.