First report of powdery mildew (Oidium carpini) on Carpinus betulus in Poland

Carpinus betulus L. is a native tree in Poland that can be found in woodlands, forests and parks throughout the country. In the cities it is often cultivated as an ornamental tree along roadsides or hedgerows. Until recently only one powdery mildew fungus (Phyllactinia guttata) had been recorded on this plant from Poland (Sałata, 1985). In 1998 however, the delicate mycelium of a powdery mildew was observed on leaves of Carpinus betulus in a hedgerow in Tarnów. In 2002 a fungus of the same appearance was found in Kraków in southern Poland. White, amphigenous mycelium covered the upper surface and less frequently lower surface, of young and older leaves of host plant (Fig. 1). No evidence of chasmothecia were found.

Hyphae were septate, branched and up to 6 µm wide. Conidiophores were erect, with straight or rarely curved foot-cells, 20-35 µm long. Conidia were solitary or in short chains, and ellipsoid-cylindrical (25-35 x 10-15 µm). Hyphal appressoria were lobed, opposite or spread along the hyphae. The morphology of this powdery mildew conformed to Oidium carpini (Braun, 1995; Braun, 1998). The specimens are preserved in Herbarium of the W. Szafer Institute of Botany in Kraków: KRAM F-53425 (specimen from Tarnów) and F-53430 (specimen from Kraków).

Oidium carpini was originally described by Foitzik from material collected in Germany (Braun, 1995). It has been also reported from Great Britain, Armenia (Braun, 1995) and Hungary (Szabó, 2003). The two localities reported here are the first records of Oidium carpini in Poland.