Research on the Pit Splitting Mechanism in Peach and a Trial to Reduce the Split-pit-induced Fruit Drop before Harvesting

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Fruits growers in Japan tend to produce big size fruits as dictated by consumer's demand. But, the treatments to promote the fruit growth also promote the split-pit and fruit drop. Previous results on the research are as follows; 1)Split-pit should be induced by the tensile force of flesh which pull sidewise the pit mainly during the period of stage II. 2)Immature seed coat drastically produces ethylene just after being exposed to air. 3)In common case of split-pit, in which the cracks are restricted in endocarp, no air is induced to seed and no ethylene is released until fruit maturation, but fruit drop is promoted before maturation.In this report, physical properties of peach fruits were investigated. Although hardiness of stone increased from stage I to stage III, the stone was estimated to be brittle and crisp during stage II. Tensile strength, plasticity and Young's modulus of the flesh in the growth promoted plot were more increased than those in the control. When pit was artificially split by injection of dye solution from the peduncle scar to the inner cavity of stone with increasing pressure, resistance force to rapture increased accompanying with the fruit development, but the values of those during stage II were statistically reduced by growth promotion, and a negative relationship between fruit diameter and the resistance force was observed.Flower bud thinning is more advisable for fruit production with better size and less split-pit, because earlier thinning may promote cell division of the remainder and secure the possibility of better fruit growth after the risky stage II. But, it is noticeable that embryo sacs of the seed in the plot of flower bud thinning were frequently deformed, in which abnormality of ploidy level by nuclear DNA was observed.