Powdery mildew on snowberry in Hungary caused by Erysiphe symphoricarpi (syn. Microsphaera symphoricarpi)

Since September 2001, powdery mildew infections have been observed on snowberry (Symphoricarpos albus) bushes grown as ornamentals in Pécs, Hungary. White superficial mycelia with abundant sporulation developed on both leaf surfaces, on the non-lignified parts of the stems (Fig. 1) and on the surface of the white fruits. Conidia were ellipsoid-doliform ranging from 25 to 36 x 10-16 μm, contained no fibrosin bodies and germinated at their ends with a single germ tube terminating in a simple or occasionally lobed appressorium. Conidia were produced singly on mostly three or occasionally two or four celled conidiophores (Fig. 2). Hyphal appressoria were mostly simple or occasionally lobed. The teleomorph stage of the pathogen was not found.

Pathogenicity was confirmed on detached healthy snowberry shoots, inoculated by touching them with powdery mildew-infected snowberry leaves. Non-inoculated shoots served as controls. Both inoculated and non-inoculated shoots were kept with ends in water within plastic bags in the laboratory. One week after inoculation powdery mildew colonies appeared on the infected leaves. No symptoms were seen on the controls. The morphological characteristics fit the anamorph of Erysiphe symphoricarpi (syn. Microsphaera symphoricarpi), a common powdery mildew species infecting Symphoricarpos spp. in North America (Braun, 1987). Its occurrence was recently reported from UK, Germany and Switzerland (Kiss et al., 2002) and also from Poland (Czerniawska & Madej 1998). Kiss et al. (2002) suggested that it was introduced to Europe from North America and showed that the internal transcribed spacer (ITS) sequences of the ribosomal DNA (rDNA) were virtually identical in the anamorphs collected in the UK and USA. In Europe, ascomata of E. symphoricarpi were only found in Germany (Kiss et al., 2002). To precisely identify the anamorph found on snowberry in Hungary, its rDNA ITS sequence was determined in a specimen collected in Pécs in 2002 and deposited at GenBank under the accession number AY322494. Sequence analysis confirmed that it belongs to the same species, E. symphoricarpi. This is the first report of powdery mildew on snowberry in Hungary. This disease has not been found outside Pécs, in spite of an intensive search conducted in five other Hungarian localities in 2002 and 2003. Herbarium specimens were deposited in the herbarium of Martin Luther University, Halle (HAL).