Abstract
In August, 1954, a virulent outbreak of blight in the field of Kennebec potatoes at Sugadaira Foundation Seed Potato Farm, Nagano Pref., was reported and blighted leaves were sent to our laboratory for the identification of race of the fungus. In the same year several leaf lesions of late blight were also found in the field of resistant hybrid varieties in Kotoni, Sapporo.
Isolates from these lesions have been proved different from the common field race through the artificial inoculation test made on several blight resistant varieties derived from S. demissum. There have been recognized two races besides common one: H3 and H7 isolates which attack Kennebec and related varieties and H2 and others which infect resistant, hybrid 48005-83. The formers do not cause lesion on the leaves of 48005-83 while the latters do not attack Kennebec.
This is the first record of new races of Phytophthora infestans in Japan.
