Evolutionary Relationships of the Dutch Elm Disease Fungus Ophiostoma novo-ulmi to Other Ophiostoma Species Investigated by Restriction Fragment Length Polymorphism Analysis of the rDNA Region

Restriction fragment length polymorphisms "RFLPs# in the ribosomal RNA gene "rDNA# region were used to assess relationships between the Dutch elm disease fungi Ophiostoma novo!ulmi and Ophiostoma ulmi\ the recently described Himalayan Dutch elm disease pathogenOphiostoma himal!ulmi\ the morphologically similar saps! tain fungi\ Ophiostoma piceae and Ophiostoma quercusand several Ophiostoma species from hardwood treesincluding Ophiostoma stenoceras and Ophiostoma proli! ferum[ A distance matrix and cluster analysis indicated that the rDNA region of O[ himal!ulmi is more closely related to those of O[ novo!ulmi and O[ ulmi than to those of O[ piceae and O[ quercus and is more distantly related to O[ stenoceras and the other Ophiostoma species\ which formed a separate clade[ The rDNA region of O[ quercus was found to be at least as closely related to that of O[ novo!ulmi and O[ ulmi as it is to that of O[ piceae[ The implications of these results for the evolution of the Dutch elm disease fungi are discussed