First report of the Dutch elm disease pathogens Ophiostoma ulmi and O. novo‐ulmi in Japan

Abstract

During a survey of Japanese ophiostomatoid fungi in 2007, 91 isolates of the Pesotum anamorph of Ophiostoma were obtained from bark of fallen Ulmus davidiana and U. laciniata trees infested by Scolytus esuriens at Akan, Kushiro and Fujimi, Kitami in Hokkaido. Growth rate, colony morphology and mating tests (Brasier, 1981) together with sequence analyses of the ribosomal ITS region, ceratoulmin (cu) gene and MAT gene DNA, were carried out on selected isolates. On this basis, isolates from both sites were identified as the Dutch elm disease pathogens Ophiostoma ulmi and O. novo-ulmi ssp. americana. The mean growth rates of five O. ulmi and five O. novo-ulmi isolates at 20°C were 2·36 ± 0·31 and 3·74 ± 0·17 mm day−1 respectively. The sequences have been deposited at DDBJ (Accession Nos. AB519191 6) and isolates deposited at the FFPRI Culture Collection, Tsukuba. During the past century O. ulmi and O. novo-ulmi have spread across Europe, North America and central Asia in two separate invasion events, causing highly destructive pandemics. Their geographic origins are unknown. Due to their considerable behavioural differences they have failed to coexist when overlapping, although transient hybrids have emerged (Brasier, 2000). This is the first report of O. ulmi and of O. novo-ulmi in Japan. There have been no previous records of Dutch elm disease in Japan (cf. Heybroek, 1982; Brasier, 1990) and no wilting of elms has been reported in the Hokkaido area. The ‘sudden’ finding of O. ulmi and O. novo-ulmi side by side in beetle breeding galleries therefore requires explanation. One possibility is that O. ulmi is endemic to Japan and O. novo-ulmi ssp. americana is a recent invasive. Genetic and field studies are in progress to assess the status and history of the two pathogens in Japan and their association with the native elms and bark beetles. The authors thank Ms Asuka Shichiri and Mr Andrew Jeeves for technical assistance. A part of this study was funded by Global Environment Research Fund of the Ministry of the Environment, Japan (F081).