Abstract
Oospore-like bodies (imperfect oospores) of the late blight fungus are formed both on the artificial cultures and on the diseased tissues of potato leaves and stems, and tomato fruits. These imperfect oospores are sorted into 4 types, as follows:
A-type: Outer wall of the spore is thin and not colored. Protoplasmic content is light yellowish brown. Without oogonium and antheridium formation.
B-type: Outer wall of the spore is light brown. Protoplasmic content is brown. Without oogonium and antheridium formation.
C-type: Outer wall of oogonium is colorless or light brown. Inner content of oospore is light to dark yellowish brown and granular. Without antheridium formation.
D-type: Oogonium is reddish brown or brown. The content of oospore is light or dark yellowish brown and granular. Without antheridium formation.
The physiology of A and B type oospores are not yet throughly studied. C and D type oospores are seemed to be formed parthenogenetically. Imperfect oospores (D type) are produced in abundance by the following culture method. When the fungus is cultured on corn extract agar for 20 to 30 days at 18°C and then transferred on oat-meal extract agar, oogonia containing oospore are found abundantly. On the contrary, when the fungus is cultured continuously on the same substrata, the oogonium is not produced. So, it seems likely that there are some stimulating actions of some nutrients on the formation of oospores.
The imperfect oospore (without antheridium) can germinate producing the germ tube or forming the sporangium.
Some of the isolates of the fungus produce only oospores but others not. When compatible isolates were paired on the same medium by means of the writers' cultural method, oogonium with the amphygenous antheridium was produced. It seems likely that the late blight fungus is heterothallic, because of the presence of the self incompatible isolates.
