Exobasidium setsutaiense sp. nov. (Exobasidiaceae) causing leaf blister on Rhododendron semibarbatum in Japan

Exobasidium setsutaiense sp. nov. is proposed to accommodate the causal agent of leaf blister on Rhododendron semibarbatum. After the examination of the herbarium materials (IUM) and newly collected fresh materials, the symptom on R. semibarbatum was clearly different from those on Rhododendron arboreum, the host of Exobasidium butleri. Morphology of basidiospores was slightly curved towards a hilum with 3–4 septa, whereas the number of septa in basidiospores of E. butleri was 0–1. The mode of germination of basidiospores was by a germ tube or by budding. The leaf blister was characterized by chlorotic leaf spot where the lesion was slightly thickened by the hyperplasia of spongy mesophyll cells. Molecular analyses of the concatenated ITS + LSU sequences supported the independence of E. setsutaiense.