First Report of Cytospora Canker Caused by Cytospora chrysosperma on White Poplar in Israel

A new disease, causing death of mature white poplar trees (Populus alba L.), was observed in Hulla Valley in northern Israel in the summer of 2002. The affected branches turned yellowish brown, and the inner bark turned black. The bark dried out and separated from the underlying wood. Later, copious, dark pycnidia developed on the dead bark. The pycnidia had a diameter of 650 µm (n = 50), ranging 600 to 800 µm. Under moist conditions, spore masses oozed out in long, reddish brown, coiled tendrils. The spores were hyaline, one-celled, and slightly curved, 1.1 × 5.5 µm (5.0 to 6.0 µm) (n = 100), and somewhat smaller than those reported by Schreiner (1). A herbarium specimen was deposited at the U.S. National Fungus Collections (BPI 843390). Isolations made from affected branches yielded colonies of Cytospora chrysosperma (Pers.:Fr.)Fr. with a whitish orange mycelium that turned dark green 11 days later. Its growth rate on potato dextrose agar at 25°C was 7.1 mm per day. Exposure to daylight induced pycnidial development after 3 to 4 weeks. Inoculation of eight 1-year-old seedlings of white poplar and willow (Salix acmophylla Boiss) proved the pathogenicity of several isolates of C. chrysosperma. The average canker length at 28 days after inoculation was 28.0 and 14.5 cm on white poplar and willow, respectively, indicating the higher susceptibility of P. alba. No cankers developed on the control seedlings. Reisolations from inoculated plants yielded C. chrysosperma. To our knowledge, this is the first report of Cytospora canker on white poplar in Israel. Reference: (1) E. J. Schreiner. Am. J. Bot.18:1, 1931.