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

根据消费者的需求，日本的水果种植者倾向于生产大尺寸的水果。但是，促进果实生长的处理也促进了裂核和落果。前期的研究结果如下：(1)裂坑主要是在第二阶段由肉的拉力引起的，肉的拉力主要向坑侧拉。2)未成熟种皮刚暴露在空气中就会大量产生乙烯。(3)裂坑的一般情况是内果皮开裂受限，在果实成熟前不诱导空气进入种子，不释放乙烯，但在成熟前促进了果实掉落。本文对桃果的物理特性进行了研究。虽然从第一阶段到第三阶段，岩石的耐寒性有所增加，但在第二阶段，岩石被认为是脆脆的。促进生长试验区果肉的抗拉强度、塑性和杨氏模量均较对照显著提高。随着压力的增加，从果柄疤痕处向果核内腔注射染料溶液人工劈裂果核，劈裂阻力随果实发育而增大，但随着生长的促进，劈裂阻力有统计学上的降低，果实直径与劈裂阻力呈负相关。对于大小较好、裂坑较少的果实，更适宜进行花芽间伐，因为早期间伐可以促进剩余部分的细胞分裂，保证危险期后果实生长较好。但值得注意的是，花蕾稀疏区种子胚囊经常发生畸形，细胞核DNA显示出倍性水平的异常。

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.