Abstract
The present paper is a result of histological and histochemical observations of the oleocellosis-like spot disease appearing on fruits of Iyo-orange (Citrus iyo Hort. ex Tanaka).
The peel of healthy area of fruits is composed of epicarp (epidermis), mesocarp and endocarp. The mesocarp comprises hypodermis, flavedo and albedo tissues. The degenerated stoma in epidermis, oil glands and vascular bundles in the flavedo tissue were recognized.
In oleocellosis type spot area, at first tangentially elongated cells developed in the flavedo tissue and then these cells died, leading to a necrotic degeneration. The cells in the flavedo tissue surrounding this area then began to divide periclinally. The necrotic cell wall gave a positive phloroglucinol-HCl reaction for the detection of lignin.
In the area of reddish-brown concave type spots, the necrotic degeneration was more extensive than in the oleocellosis type spot. In case of the convex spots (scab-like) phellem developed remarkably under the necrotic cells and the spots raised as the result of abnormal division of phellogen and the formation of abnormal meristem.
These observations suggested that all the types of spots are merely the representative of symptoms recognizable in the developmental process of identical disease, the oleocellosis-like spot, although the causal agent of this disease has not so far been elucidated.
