China and the origins of Dutch elm disease: an appraisal

Circumstantial evidence has led to the widespread assumption that Dutch elm disease (caused by Ophiostoma ulmi ) spread to Europe and North America from China. The author's recent surveys indicate that the disease is probably absent from China, and only a relatively recent arrival in the Soviet Tien Shan mountain region on the western Chinese border. Alternative origins for the disease include introduction from the Himalayas, and recent rapid evolution within Europe from a fungus such as Ophiostoma piceae . Elucidation of the various possibilities is complicated by the need to account for the spread of at least three genetically divergent subgroups of the pathogen.