The characteristic disorders occuring on fruit skin in 'SaiJo' were vertically striped and broken line-like types of black stain. These seem to be primarlly caused by rapid enlargement of fruit in the late stage accompanied by the expansion of fine splits on skin, and secondly caused by the oxidation of polyphenol substances in the epidermal and sub-epidermal cells exposed to air and rain water.
'SaiJo'was compared with black stain-free 'Fuyu' on the contents of ascorbic acid（total and reducing type), a reducing substance, from the early stage of coloring to the harvest. In the later stage of fruit growth, the content of reducing type ascorbic acid in peel differed largely in these cultivars. In 'Saijo' it decreased succesively from 13 mg % at the middle stage of coloring to 2 mg % at harvest, whereas in 'Fuyu' increased from 5-6 mg % to 60 mg %.
Repeated spray applications of 0.2 % L-ascorbic acid and 0.2% L-ascorbic acid plus 0.5% citric acid in late season considerably reduced vertically striped type of black stain in 'Saijo'. However, they did not show no apparent influence on other types.