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

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L. Kiss a*, L Vajnaa and G. Fischlb

a Plant Protection Institute, Hungarian Academy of Sciences, H-1525 Budapest, PO Box 102, Hungary
b University of Veszprém, Georgikon Faculty of Agriculture, H-8360 Keszthely, Deák Ferenc Street 57, Hungary

*lkiss@nki.hu

Accepted for publication 28 Nov 2003

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.
Figure1
Figure 1: Powdery mildew colonies on a horse chestnut (A. hippocastanum) leaf.
Figure2
Figure 2: Appendages of an ascoma of E. flexuosa. A. Long appendages terminating in circinate tips. B. Short, bristle-like appendages.
Acknowledgements

This work is a part of a study supported by three grants (OTKA F32931, OTKA T042-494 and NKFP 4/008/2001) and by a János Bolyai Research Fellowship awarded to LK.
References

Ale-Agha N, Braun U, Feige B, Jage H, 2000. A new powdery mildew disease on Aesculus spp. introduced in Europe. Cryptogamie Mycologie 21, 89-92.

Bolay A, 2000. L'oidium des marronniers envahit la Suisse. Revue suisse de Viticulture, Arboriculture et Horticulture 32, 311-13.

Ing B, Spooner B, 2002. The horse chestnut powdery mildew Uncinula flexuosa in Europe (New British Record 210). Mycologist 16, 112-13.

Szentiványi O, Varga K, Kiss L, 2003. Powdery mildew on snowberry in Hungary caused by Erysiphe symphoricarpi (syn. Microsphaera symphoricarpi). New Disease Reports [http://www.bspp.org.uk/ndr/] Volume 8.

Zimmermannova-Pastircakova K, Adamska I, Blaszkowski J, Bolay A, Braun U, 2002. Epidemic spread of Erysiphe flexuosa (North American powdery mildew of horse-chestnut) in Europe. Schlechtendalia 8, 39-45.

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