Lilac (Syringa vulgaris L.) is a popular ornamental woody plant grown for its very decorative flowers and large, dark-green leaves. The leaves remain on the shrubs for a long time. The fungus, Ascochyta syringae, is a pathogen which deteriorates the decorative value of the leaves. It causes brown irregular spots on leaves. In this study, 20 fungal isolates were tested in terms of their pathogenicity towards the leaves of S. vulgaris, and mycelium growth rate, while genetic variability was determined by RAPD-PCR. It was found that some isolates do not cause the formation of brown spots on leaves. Isolates differed considerably in terms of mycelium growth rate, ranging from 0.5 mm day^-1 (B96 at 30°C) to 8.8 mm day^-1 (B92a at 25°C). A positive dependence between mycelium growth and the capacity to cause leaf spots was observed. No close dependence was found between the genetic variability of isolates and the other examined traits of the isolates.

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