Abstract
Pythium amaminum sp. nov. was isolated from river and reservoir water on Amami island, Kagoshima Prefecture, Japan. The species can grow at temperatures between 10 °C and 35 °C. At the optimum temperature of 25 °C, the radial growth rate is 22.5 mm per day. Pythium amaminum produces filamentous sporangia consisting of branched, lobulate or digitate elements forming large complexes. Zoospores form inside the vesicle, which is discharged through a long tube at least 320 μm. Globose oogonia are ornamented with conical blunt spines. Oospores are aplerotic and globose. Antheridia twine around the oogonia or stick to them. These features having a both of the long discharge tube from sporangium and oogonia with spines are not observed in any other species of the genus Pythium, and thus we conclude that P. amaminum is a new Pythium species.