MITOCHONDRIAL-DNA RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS OF AGGRESSIVE AND NONAGGRESSIVE ISOLATES OF OPHIOSTOMA-ULMI

Mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs) of 12 aggressive and 6 non-aggressive isolates of Ophiostoma ulmi (Buism.) Nannf. from 6 countries were investigated. Mitochondrial DNAs from O. ulmi budding cells were isolated by bisbenzimide-Cesium Chloride buoyant density centrifugation, digested using either of the restriction endonucleases Eco R1, Bgl II, Bam HI, Hin dIII, Pst I or Pvu II, electrophoresed on 0.8% agarose gels, stained in ethidium bromide and viewed under UV light. Five out of the six endonucleases showed the presence of characteristic mtDNA polymorphisms for each group of isolates. Minor polymorphisms were also observed within the aggressive and the non-aggressive groups. The size of the mitochondrial genome was 40% greater for the non-aggressive isolates than for the aggressive isolates. Plasmid-like nucleic acids were found in 3 isolates. RFLP markers may, therefore, provide a new means for the identification of aggressive and non-aggressive wild type isolates of O. ulmi.