Photinia × fraserii, belonging to the family Rosaceae, is an evergreen shrub used in parks and gardens. During the spring of 2004, severe outbreaks of a previously unknown powdery mildew were observed in a public park at Torino (northern Italy) on established plantings of this species. The adaxial and abaxial surfaces of leaves were covered with white mycelium and conidia. Stems also had signs of powdery mildew and were chlorotic. As the disease progressed, infected leaves turned yellow and abscised. Conidia formed in chains and were hyaline, ellipsoid, and measured 16.8 to 33.6 × 12.0 to 24.0 μm (average 25.6 × 15.6 μm). On the basis of host, morphological characteristics, and the presence of fibrosin bodies, the pathogen was identified as Podosphaera leucotricha (Ellis & Everth.) E.S. Salmon (2). Pathogenicity was confirmed by inoculating young leaves of 2-year-old Photinia × fraserii plants with a spore suspension (3 × 105 spores per ml). Also, three 3-year-old cv. Golden Delicious potted apple plants were inoculated. Three noninoculated Photinia × fraserii and three noninoculated apple plants sprayed with deionized water served as a control. After inoculation, plants were maintained in a growth chamber at 25°C. After 17 days, powdery mildew symptoms were observed on inoculated plants of Photinia × fraserii and cv. Golden Delicious. Noninoculated plants remained healthy. The pathogenicity test was carried out twice. The pathogenicity on apple supported the identification of the pathogen as P. leucotricha. To our knowledge, this is the first report of powdery mildew on Photinia × fraserii in Italy. P. leucotricha was previously described on Photinia serrulata in Italy (1) and the United States (3). Voucher specimens are available at the AGROINNOVA Collection, University of Torino.
References: (1) E. Baldacci. Rev. Appl. Mycol. 16:358, 1937. (2) R. T. A. Cook et al. Mycol. Res. 101:975, 1997. (3) J. A. Milbraith. Rev. Appl. Mycol. 17:751, 1938.
