Occurrence of Erysiphe flexuosa (syn. Uncinula flexuosa) on horse chestnut (Aesculus hippocastanum) in Hungary

In August 2002, horse chestnut (Aesculus hippocastanum) trees exhibiting the symptoms of powdery mildew infections were observed in two Hungarian localities around the lake Balaton. In 2003, powdery mildew infections of horse chestnut trees were also observed in two other cities (Keszthely and Budapest) in Hungary. White powdery mildew colonies appeared and spread on the upper (Fig. 1) and the lower leaf surfaces of both young and old leaves. Conidia were cylindric to doliform, measured 23-37 x 8-16 μm and were produced singly on 2-3 celled conidiophores. Hyphal appressoria were mostly lobed or multi-lobed. Ascomata were produced in abundance, mostly on the lower leaf surfaces. These measured 82-148 μm in diameter, contained 6-10 asci and bore two types of appendages: long ones terminating in circinate tips as well as short, bristle-like ones. The long appendages measured 58-182 μm and their upper halves were undulate (Fig. 2A). The shorter ones measured 12-32 μm and were straight and thick-walled (Fig. 2B). The pathogen was identified as Erysiphe flexuosa (syn. Uncinula flexuosa), a North American powdery mildew species recently introduced to Europe (Ale-Agha et al. 2000; Ing & Spooner 2002). Pathogenicity was confirmed in a test conducted as described in Szentiványi et al. (2003) for snowberry powdery mildew. Herbarium specimens were deposited in the herbarium of Martin Luther University, Halle, Germany (HAL).

The epidemic spread of this North American pathogen has already been reported from Germany (Ale-Agha et al., 2000), Switzerland (Bolay, 2000), England (Ing & Spooner, 2002) and some other European countries (Zimmermannova-Pastircakova et al., 2002). This is the first report of E. flexuosa from Hungary.