Abstract
On the diseased leaves of some species of Platanus, Cercospora platanifolia ELLIS et Ev. is commonly associated with a fungus bearing dark brown, short conidia, which is very similar to Stigmina platani (FUCK.) SACC. in conidial shape. The authors at first considered that the lesions caused by Cercospora platanifolia were probably contaminated with Stigmina platani. Following further detailed investigation, however, this assumption was totally denied.
Cercospora platanifolia has two different types of conidia, Cercospora and Stigmina. Between these distinct conidial types, many transformed conidia are observed, and all of these types of conidia are able to be arranged successively.
On the diseased leaves there are noticed two types of lesions, the necrotic spot and the sooty lesion. The necrotic spots are usually found on young succulent leaves, while the sooty lesions develop on mature hard leaves.
In the early part of September in Tokyo, almost all of the conidia on both necrotic and sooty lesions are Cercospora-type, interspersed with a very few of Stigmina-type conidia. With the advance of the seasons, the number of Stigmina-type conidia found becomes gradually larger, and, on the contrary, that of Cercospora-type conidia becomes smaller.During the middle of November a larger percentage of conidia on both necrotic and sooty lesions are Stigmina-type. This variation occurs more rapidly on the sooty lesion than on the necrotic spot.
The perfect stage of the fungus is rarely found on the overwintered diseased leaves in spring, and this is a member of the genus Mycosphaerella. In the morphological characteristics the Mycosphaerella is not accordant with either M. platanifolia COOKE or M. stigmina-platani WOLF.
Overwintering of the fungus is mainly made by Stigmina-type conidia, which have germinability under natural conditions till the following spring and cause the primary infection of the disease. Accordingly, Stigmina-type conidia of the fungus are considered to play an important role in overwintering.
