INHERITANCE OF CHROMOSOME-LENGTH POLYMORPHISMS IN OPHIOSTOMA-ULMI (SENSU-LATO)

We have investigated the mitotic and meiotic transmission of chromosom e-length polymorphisms in Ophiostoma ulmi s.l., the causal agent of Du tch elm disease. The North-American aggressive (NAN) strain CESS16K ha s an atypical electrophoretic karyotype, carrying two chromosome-sized DNAs (chDNAs) that have not been observed in other members of the NAN biotype. Independent CESS 16K chDNA preparations, even after repeated inoculation and recovery from the elm host, and analysis of 16 progen y strains after a cross between the NAN strains FG245B(r)-O and CESS 1 6K, demonstrated that these unique chDNAs are integral components of t he CESS 16K genome. Analysis of the progeny, by electrophoretic karyot yping and hybridizations with probes specific to individual chDNAs, pr esented evidence that genome rearrangements can occur as a consequence of meiosis. Even though novel electrophoretic karyotypes and a novel- sized chromosome were observed in the karyotypes of the progeny strain s, the low level of reassortment between the chromosomes carrying leng th polymorphisms presented evidence that there are constraints to geno me plasticity for this fungus.