Morphology, vegetative compatibility and pathogenicity of Verticillium dahliae isolates from woody ornamentals in GermanyMorphologie, vegetative Kompatibilität und Pathogenität von Verticillium dahliae-Isolaten aus Ziergehölzen in Deutschland

Isolates of Verticillium dahliae were collected from affected woody ornamentals in German tree nurseries. Nitrat non-utilizing mutants were produced and vegetative compatibility groups (VCGs) were identified based on complementation tests. The results of this study indicate that VCG diversity of V. dahliae in German is limited, because only two VCGs were detected. Of the 32 isolates analysed, 19 were classified as VCG D1 and 13 as VCG D2. VCG D1 was compatible with the American VCG 2B, whereas VCG D2 was compatible with VCG 4B. In morphological studies a significant correlation between the conidial length of the V. dahliae isolates and their VCG could be detected. Isolates from VCG D1 consistently formed small conidia with an average length of 3,78:gmm, whereas isolates from VCG D2 produced larger conidia with an average length of 4,36:gmm. Pathogenicity tests were carried out with isolates on Acer platanoides, Acer pseudoplatanus, Catalpa bignonioides, Castanea sativa, Fraxinus excelsior and Tilia cordata. The isolates showed little significant differences in their aggressiveness to certain hosts. No major differences in virulence between VCGs were observed. The results imply that VCG identification does not contribute to verticillium disease prediction for a range of woody hosts.