First report of Erysiphe palczewskii on Caragana arborescens in the Czech Republic 

Caragana arborescens (Siberian peashrub) is an important ornamental deciduous shrub that is grown in ca 30% of the parks and amenity areas in the Czech Republic. During the summer of 2006 and 2007, in a private garden in Smržice (Central Moravia, Czech Republic), a severe powdery mildew infection was recorded on two C. arborescens var. Pendula shrubs. Superficial white sporulating mycelium was found covering both the upper and lower leaf surfaces, interspersed with patches of chasmothecia (Fig.1). In the same garden, powdery mildew symptoms were also seen on C. arborescens var. Lorbergii.

The hyphae were branched, 5-7 μm wide, with slightly lobed appressoria. Conidia were formed singly (Pseudoidium type) and were cylindrical, lacking fibrosin bodies, 20-37.5 mm long and 8.75-17.5 mm wide. Conidiophores were erect, 45-92.5 mm, with foot-cells that were straight 15-40 mm, followed by 2-3 distal cells (Fig.2). Chasmothecia were hyaline, mycelioid, thin-walled, smooth, 67.5-112.5 mm in diam., with 4-13 appendages that were dichotomously branched at the apex, measuring 180-330 mm and 1.8-4.1 times as long as the chasmothecial diameter (Fig.3.). The asci were short-stalked, 3-8 per chasmothecium, 47.5-77.5 mm long and 22.5-42.5 mm wide, containing 3-8 ellipsoid-ovoid ascospores 17.5-27.5 mm long and 8.75-16.25 mm wide (Fig.4).

Braun (1995) confirmed the occurrence in Europe of at least two powdery mildew species on the genus Caragana; Microsphaera trifolii var. trifolii and M. palczewskii. Our measurements are in agreement with those given by Braun (1995) for Microsphaera palczewskii (syn. Erysiphe palczewskii, Braun & Takamatsu, 2000). E. palczewskii is native to Asia, however in recent decades it has been introduced into several European countries and has now become one of the most widespread powdery mildews in eastern Europe (Braun, 1995; Heluta & Minter, 1998). More recently the fungus has also been introduced into North America (Nischwitz & Newcombe, 2003). To our knowledge this is the first record of this species on C. arborescens in the Czech Republic.