Three species of Exobasidium causing Exobasidium leaf blight on subgenus Hymenanthes, Rhododendron spp., in Japan.

Three Exobasidium species causing Exobasidium leaf blight on Rhododendron of subgenus Hymenanthes in Japan are described and discussed. After examining the holotype and fresh materials of E. shiraianum on R. degronianum, its description is emended by the morphology of basidiospores that are ellipsoid to ovoid, or obovoid, 11–21 × 5–8 µm, and with 1–3 septa. Culture of this species showed yeast-like growth. Exobasidium woronichinii on R. brachycarpum observed from Hokkaido Prefecture to Nagano Prefecture is described as a new species characterized by its ellipsoid to ovoid, 11–19 × 3–4.5 µm, and 1–5(–6)-septated basidiospores. Culture of this species was gelatinous but obtrite, or thick and showed farinose appearance by conidiation. A fungus on R. aureum in Hokkaido and Nagano Prefectures is identified as E. caucasicum. This species is new to Japan and is characterized by its ellipsoid to ovoid, or obovoid, 11–19 × 3–6 µm, and 0–2-septated basidiospores. Culture of this species showed yeast-like growth.