EVALUATION OF VULNERABILITY TO SPLIT-PIT IN PEACH FRUIT BY A PRESSURE CHAMBER

Vulnerability to split-pit of peach was investigated with a pressure chamber. Fruit was set outside the chamber. A dye solution set inside the chamber was injected with pressure through a hypodermic needle from the peduncle scar to the cavity of pit. The pit, in most cases with flesh, was artificially split by increasing air pressure, which was monitored with a pressure sensor. The maximum resistance force of the pit to rupture increased during fruit development from ca. 0.5 MPa at middle stage 1 to ca. 2.0 MPa at late stage 3. In the stage 2, the maximum pressure of growth-promoted fruit by thinning treatment was significantly reduced compared to that of the control unthinned fruit. There was a negative relationship between fruit diameter and the maximum resistance force against pressure. As well as the fruit diameter over 45 mm, the maximum pressure value under 1.0 MPa should be an indicator for being vulnerable to split-pit during the stage 2. A trial of fruit growth promotion by flower bud thinning, followed by standard fruit thinning management, yielded a satisfactory level of fruit growth and reduced the percentage of split-pit to an acceptable level. Flower bud thinning is advisable for peach fruit production to induce better size and less split-pit, because earlier thinning may promote cell division and secure the possibility of better fruit growth after the risky stage 2. However, it is noticeable that the embryo sac of the seed in growth-promoted fruit was frequently deformed, and ploidy of the embryo and endosperm was abnormal.