In June 2013, we collected leaf spot disease samples of Datura metel from Gangneung, Gangwon Province,
Korea. The symptoms observed were small circular to oval dark brown spots with irregular in shape
or remained circular with concentric rings. We isolated the pathogen from infected leaves and cultured the
fungus on potato dextrose agar. We examined the fungus morphologically and confirmed its pathogenicity
according to Koch’s postulates. The results of morphological examinations, pathogenicity tests, and the rDNA
sequences of the internal transcribed spacer regions (ITS1 and ITS4), glycerol-3-phosphate dehydrogenase
(G3PDH) and the RNA polymerase II second largest subunit (RPB2) gene sequence revealed that the causal
agent was Alternaria tenuissima. To the best of our knowledge, this is the first report of leaf spot of D. metel
caused by A. tenuissima in Korea as well as worldwide.