Studies on ‘Kohansho’: a physiological disorder of fruit rind in Hassaku (Citrus hassaku Hort. ex Tanaka)

Abstract

Experiments were carried out over a five year period to clarify the conditions Causing ‘Kohansho’ on Hassaku (Citrus hassaku Hort. ex Tanaka) fruit.
Kohansho seldom developed under storage conditions of 7 to 8°C, 90+5%RH, but appeared 2 or 3 days after removal from storage. The severest symptoms after storage were found on fruits harvested in late December.
Kohansho was suppressed by waxing or dipping the fruits in water at 50°C for 5min, but became more pronounced when the fruits were dipped in a 2% solution of CaCO₃. The symptoms became more severe at temperatures of 15-20°C and less severe at 7-8°C after removal from storage.
Very few symptoms were observed in fruits from Hassaku trees grown in a plastic greenhouse, and the respiration and ethylene evolution rate of these fruits also showed little change after being transferred from storage.
Dipping fruit in wax or hot water increased the level of CO₂ and decreased the level of O₂ within the fruits. Occurrence of Kohansho is discussed in relation to these gas conditions within the fruit, and to respiration and ethylene evolution of the fruit.