FIRST REPORT OF THE POWDERY MILDEW AGENT ERYSIPHE FLEXUOSA ON AESCULUS XCARNEA IN ITALY

Abstract

Aesculus hippocastanum L. (horse chestnut) and Aesculus x carnea Hayne (red horse-chestnut) are ornamental tree species commonly grown in parks, gardens and boulevards. In October 2012, typical symptoms of powdery mildew were observed on the leaves of several A. x carnea trees in the University campus of Grugliasco (Piedmont, northern Italy). Trees were 12-year-old, about 6 m tall and their trunk was ca. 20 cm in diameter. Whitish fungal mycelium and abundant cleistothecia were visible macroscopically on the both the upper and lower leaf surfaces. Cleistothecia were yellow or light brown, turning dark brown to black at maturity. They were globose, 98.4 to 123 μm in diameter (105.6 μm in average), with hooked and undulate appendages 108.2- 147.6 μm long (123 μm in average); short, bristle-like appendages were also observed. Cleistothecia contained several asci, whose ascospores were hyaline, ellipsoid and single- celled (17-28 x 9-13 μm). Based on these micro-morphological characters, the fungus was identified as Erysiphe flexuosa (Peck) U. Braun et S. Takam. (syn. Uncinula flexuosa), a powdery mildew introduced from North America and now reported from Aesculus spp. in several European countries (Tozlu and Demirci, 2010). Reports from Italy are limited to A. hippocastanum (Parrini and Braccini, 2003). Therefore, to our knowledge, this is the first report of E. flexuosa on A. x carnea in Italy.