Taxonomy of Exobasidium otanianum causing Exobasidium leaf blight on Rhododendron species in Japan

Exobasidium otanianum var. otanianum and var. satsumense have been reported as causal pathogens of Exobasidium leaf blight on Rhododendron species. Specimens of both varieties including types were morphologically examined. The type specimen of var. otanianum had 0–4-septated basidiospores although 1(–3)-septated basidiopores were reported in the original description. Observations of its herbarium specimens from different localities and its fresh materials from the type locality also confirmed the septal number of its basidiospores. Exobasidium otanianum var. satsumense was morphologically similar to var. otanianum, including the septal number of basidiospores. Germ tubes were consistently produced in these two varieties. From these observations, var. satsumense is treated as a synonym of var. otanianum and the description of E. otanianum is emended. Rhododendron hyugaense and R. reticulatum f. glabrescens are newly added to host plants of E. otanianum.