Diagnosis of Witches' broom disease on Rhododendron kaempferi including the natural monument in Yamanashi, Japan

Abstract

Since 1993, tree decline and witches' broom have been observed on Rhododendron kaempferi including the national natural monument tree, Ooyamatsutsuji, in Utsukushimori, Hokuto, Yamanashi, Japan. Witches' broom on branches and trunk were observed year-round. The abaxial side of young leaves on diseased branches was covered with white hymenia in June. The symptom was similar to Exobasidium leaf blister. Based on morphological observation and molecular analyses of rDNA-ITS and LSU regions, the fungus isolated from the symptoms was identified as E. pentasporium. This is the first report identified the causal agent of the witches' broom diseases in this area. It suggests that this epidemic disease may be one of the factors for the decline of the plants.