Molecular relationships between Ophiostoma ulmi and the NAN and EAN races of O. novo-ulmi determined by RAPD markers

Abstract

Thirty-six isolates of Ophiostoma ulmi and O. novo-ulmi (EAN and NAN races) were compared using randomly amplified polymorphic DNA (RAPD) markers. The separation of three distinct clusters, and the quantitative relationships between them, is in good agreement with the designation of 0. ulmi and O. novo-ulmi as distinct species and the designation of the EAN and NAN races of 0. novo-ulmi as closely related but distinct biological entities. The RAPD analysis was found to be more sensitive than restriction fragment polymorphism (RFLP) analysis of the same isolates, and allowed variation within each of the three taxa to be detected. Some isolates from widely separated geographical locations had identical RAPD and RFLP profiles indicating the likely route of spread of individual genotypes of the fungus. Occasionally isolates with identical RAPD and RFLP profiles differed in their vegetative compatibility (vc) group, suggesting positive selection of vc mutants, possibly as a result of their remaining free from deleterious virus-like cytoplasmic agents (d-factors). The results are discussed in terms of hypotheses regarding the evolution of the EAN and NAN races.