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 dise ase fungi Ophiostoma novo-ulmi and Ophiostoma ulmi, the recently described Himalayan Dutch elm disease pathogen, Ophiostoma himal-ulmi, the morphologi cally similar sapstain fungi, Ophiostoma piceae and Ophiostoma quercus, and several Ophiostoma species from hardwood trees, including Ophiostoma steno ceras and Ophiostoma proliferum. A distance matrix and cluster analysis ind icated that the rDNA region of O. himal-ulmi is more closely related to tho se of O. novo-ulmi and O. ulmi than to those of O. piceae and O. quercus an d is more distantly related to O. stenoceras and the other Ophiostoma speci es, 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 ann O. ulmi as it is to that of O. piceae. The implications of these results for the evoluti on of the Dutch elm disease fungi are discussed.