Genetic and Molecular Characterization of Verticillium dahliaeIsolates from Woody Ornamentals in Belgian Nurseries

Isolates of Verticillium dahliaewere collected from affected trees (Acerspp., Tiliaspp. and Robiniaspp.) and soils in Belgian ornamental nurseries. Nitrate non-utilizing mutants were produced and vegetative compatibility groups (VCGs) were classified based on complementation tests with reference tester strains. Of the 30 isolates analysed, 12 were classified as VCG2B and 18 as VCG4B following the American classification. In order to distinguish VCG2B from VCG4B, specific polymerase chain reaction primers were designed based on the sequence of a VCG2B-associated Direct Amplification of Minisatellite-region DNA (DAMD) band generated with the core sequence of the phage M13 minisatellite DNA. Using this test, amplification products were generated for all the VCG2B isolates characterized in this study. In contrast, no signal was seen on ethidium–bromide agarose gel for VCG4B isolates. Pathogenicity tests were carried out in a glasshouse on maple-rooted cuttings inoculated with conidial suspensions of V. dahliaebelonging to both groups (VCG2B/VCG4B). Some strains proved to be highly aggressive, while others did not. However, these different behaviours were not correlated with the VCGs.