Honeysuckle (Lonicera caprifolium L., family Caprifoliaceae) is a climbing shrub used in gardens to cover walls and supports. During the summer of 2003, severe outbreaks of a previously unknown powdery mildew were observed on this species in some gardens near Biella (northern Italy). The first symptoms included extensive chlorosis on leaves, followed by the appearance of white mycelium on the adaxial and abaxial leaf surfaces. As the disease progressed, infected leaves turned yellow and died. Conidia were hyaline, ellipsoidal, and measured 27.6 to 43.2 × 12.2 to 21.6 μm (average 35.7 × 17.6 μm). Foot cells were cylindric and appressoria lobed. Fibrosin bodies were not present. Cleistothecia were not observed during the growing season. The pathogen was identified as Oidium subgenus Pseudoidium (2). The inoculation procedure involved gently pressing diseased leaves onto leaves of healthy L. caprifolium plants. Three plants of L. caprifolium were used as replicates. Noninoculated plants served as control. Inoculated and noninoculated plants were maintained in a garden at temperatures ranging from 15 to 25°C. 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 powdery mildew on L. caprifolium in Italy. The presence of powdery mildew on different species of Lonicera has been reported in several countries, particularly, Microsphaera miurae U. Braun on L. morowii A. Gray in Germany (1), M. lonicerae (DC.) Winter on L. peryclimenum L. in England (3), and M. lonicerae-ramosissimae on L. ramosissima Fr. & Sav. in Japan (4). The conidia of M. lonicerae are smaller than those of the Oidium sp. reported on L. caprifolium. Voucher specimens are available at DIVAPRA Collection at the University of Torino.
References: (1) U. Braun. Mycotaxon 16:417, 1983. (2) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000. (3) J. Robbins. Cecidology 15:15, 2000. (4) S. Tanda. Mycoscience 41:155, 2000.