Akebia quinata Decne., an ornamental species belonging to the family Lardizabalaceae, is used as a climbing species in gardens to cover walls as well as supports and is very much appreciated because of its dark red flowers. During the summer of 2003, severe outbreaks of a previously unknown powdery mildew were observed on established plantings in several gardens near Biella (northern Italy). The upper surfaces of leaves were covered with white mycelium, and the corresponding abaxial surface of infected leaves were chlorotic. Young, green stems also affected showed extended chlorosis. As the disease progressed, infected leaves turned yellow and died. Foot cell was cylindric and appressorium lobed. Conidia formed singly were hyaline, ellipsoid, and measured 26.4 to 45.6 × 10.6 to 15.6 μm (average 35.1 × 12.7 μm). Fibrosin bodies were not present. The pathogen was identified as Oidium sp. subgenus Pseudoidium (1) partially because cleistothecia were not observed. Conidial measurements are close to those reported for Microsphaera akebiae Sawada. Pathogenicity was confirmed by gently pressing diseased leaves onto leaves of healthy A. quinata plants. Three plants of A. quinata were used as replicates. Noninoculated plants served as controls. Plants were maintained between 20 and 30°C in a garden located 5 km from where the disease was originally found. After 10 days, typical symptoms of powdery mildew developed on inoculated plants. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of the presence of powdery mildew on A. quinata in Italy. The disease is currently restricted to the area of Biella. The presence of M. akebiae was recently reported in the Netherlands (2). Specimens of this disease are available at the DIVAPRA Collection at the University of Torino.
References: (1) U. Braun and S. Takamatsu. Schlechtendalia, 4:1, 2000. (2) M. Scholler and W. Gams. Nova Hedwigia, 67:101, 1998.