Powdery mildew caused by Erysiphe carpinicola on Carpinus betulus in Hungary: the first European report

The European Hornbeam, Carpinus betulus, is a common, native forest and ornamental tree of central Europe, including Hungary. This tree is generally regarded as being largely free from infection by fungal pathogens. However, in July 2005, typical symptoms of powdery mildew were observed on leaves of 25-30 year old European Hornbeam trees in Városmajor Park, Budapest and later in three other parks in the city. White, epiphytic mycelia and conidia were present on both sides of leaves, forming thin, irregular colonies (Fig. 1). Affected areas appear faintly chlorotic. In late summer, infected leaves often become completely chlorotic with occasional green islands associated with the infected areas. Later, during September and October, scattered chasmothecia appeared mainly on the upper leaf surface and were associated with the infected area. (Fig. 2a & b). Infection was severe on many trees.

 

Hyphae up to 6 µm wide; conidiophores mostly erect with cylindrical foot cells (65-72 µm; Fig. 3); conidia develop singly, ellipsoid-ovoid, (13.6 x 34.6 µm (12.5-15.0 x 30.0-38.8 µm); chasmothecia subglobose (90-136 µm), with irregularly polygonal cells (Fig. 2 c), equatorial appendages (6-21 per chasmothecium; Fig 2a & b) flexuous or seldom straight, hyaline, smooth, apex closely or loosely circinate (sub helicoid) (Fig. 2d), 1.4-2.6 times as long as the chasmothecial diameter; asci 4-6 per chasmothecia, sessile or shortly stalked, 6-8 spored (Fig. 2e); ascospores were hyaline, ellipsoid-ovoid, measuring 13.4 x 22.7 μm (10.0-15.0 x 17.5-25.0 µm). Based on this morphology the powdery mildew fungus conformed to Erysiphe carpinicola (syn. Uncinula geniculata var. carpinicola; Braun & Takam, 2000). The specimens are preserved in the Herbarium of the author (Plant Protection Institute, Budapest, accession number: Ec 1-10/2005).

This fungus was originally recorded in Japan and later observed from the far east of the former USSR to China (Braun, 1987). Recently a record of this species, given as Uncinula carpinicola, infecting C. betulus in the Crimean Penninsula, was included in the fungal database: http://www.cybertruffle.org.uk. This Ukrainian data was taken from the "Electronic Distribution Maps of Ukrainian Fungi and Plants"; a non-referred source. Therefore this is the first definitive report for Erysiphe carpinicola in Europe, in addition to being the first report of this pathogen in Hungary.