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First Report of Puccinia lagenophorae on Common Groundsel (Senecio vulgaris) in Canada

Rust disease on common groundsel was independently collected from two backyard gardens in Alberta, Canada during 2005, the first on September 11 in Sherwood Park (53.542°N, 113.262°W) and the second on September 18 in Edmonton (53.463°N, 113.593°W). Leaves of each specimen had clusters of orange, cup-shaped aecia, bordered by recurved peridia, the principal macroscopic signs of disease. Infected plants had twisted stems and deformed leaves. Spores of isolates from the two locations were (mean diameter [± s.d.; range]) 14.6 (± 1.4; 11.4 to 18.9) × 12.5 (± 1.1; 9.1 to 16.2) μm, orange, oval or angular, and many had refractive granules (3). Genomic DNA was extracted from small leaf pieces with multiple aecia, and the complete internal transcribed spacer (ITS) region of the rust was sequenced from PCR products. The sequences determined for a representative specimen from each location were identical, including two areas of ambiguity in the ITS1 spacer region. At position 7 were two overlapping peaks (A and C), and near position 130, sequencing failed because of a suspected insertion/deletion in some ITS copies. Difficulties of sequencing through this cytosine-rich area were reported by Littlefield et al. (3). Data from cloned PCR products confirmed the presence of two ITS genotypes in each DNA extract, one identical to a sequence published for Puccinia lagenophorae on Senecio vulgaris from the United Kingdom (GenBank Accession No. AY808060 (2), and the other identical to a sequence from the United States (GenBank Accession No. AY852264) (3). They differ by an A/C transversion at position 7 and an indel, an 8/9 base poly-C run beginning at position 130. Telia and teliospores were not observed in any of the 2005 samples (some collected as late as November) or in the 2006 Edmonton site samples. Identification of the pathogen as P. lagenophorae was based on host plant symptoms (3) and molecular characters. The original source of inoculum for these infections is unknown, but on December 5, 2006, diseased specimens with sporulating aecia were found beneath 45 cm of snow at the Edmonton location, in a garden area that had not been weeded during the summer. There is reported evidence that teliospores are not functional and that P. lagenophorae overwinters on infected plants that develop aecia in the spring (1). Specimens have been deposited at the Arthur Herbarium, Purdue University, West Lafayette, IN (Vouchers PUR N5414--N5417) and the National Mycological Herbarium of Canada, Ottawa, ON (Vouchers DAOM 237844, 237845, 237961, 237962, 237982, and 237990). The two cloned variants of the ITS sequence were deposited in GenBank (Accession Nos. EF212446 and EF212447). To our knowledge, this is the first report of groundsel rust caused by P. lagenophorae in Canada (G. Barron, personal communication, has images from Guelph in 2004 but no specimens were examined or preserved). Groundsel rust has been found at several locations in the United States (3) and has been reported on more than 60 species in several genera (4). Questions remain about the amount of damage that P. lagenophorae will cause to groundsel in North America and whether it will affect native Senecio species and their relatives.

References: (1) J. Frantzen and H. Müller-Schärer. Plant Pathol. 48:483, 1999. (2) B. Henricot and G. Denton. Plant Pathol. 54:242, 2005. (3) L. Littlefield et al. Ann. Appl. Biol. 147:35, 2005. (4) M. Scholler. J. Plant Dis. Prot. 105:239, 1998.