Anatomical Observation on Ulcerous Kohansho and Similar Disorders on the Peel Surface of Yuzu (Citrus junos Sieb. ex Tanaka) Fruit

Abstract

Two typical symptoms of ulcerous Kohansho, the convex and concave types, frequently appear on the flavedo of Yuzu (Citrus junos Sieb. ex Tanaka) fruit. The external appearances of these two symptoms and similar disorders caused by painting with crushed peel juice or pricking with a thorn were compared by histochemical examination.
1. In cross sections of the ulcerous Kohansho, a fan-shaped, degenerated region and the central vascular bundles on the same side of the fruit were always observed.
The convex type symptom at first appeared as a blackish, oily spot which changed to a milky white spot and finally, to a brown, convex spot. Histochemical analysis revealed that the region consisted of small, irregularly shaped cells surrounding the degenerated region in whose margins, the cell walls were lignified and suberized layers were observed. The concave injury was accompanied by small, irregularly shaped cells which were lignified but the suberized layers were not noticeable.
2. In regions damaged by painting with crushed peel juice, the degenerated part was not fan-shaped and the degeneration proceeded parallel to the epidermis. Vascular bundles were not observed in the degenerated region.
3. Areas damaged by pricking with a thorn remained clear even after lignification and suberization of the tissue had advanced so that it is possible to distinguish that injury from that caused by ulcerous Kohansho.
These observations led us to conclude that the degenerating processes in the typical ulcerous Kohansho differed histologically from those caused by crushed peel juice or mechanical injury.