In April 2005, a rust fungus on Pennsylvania blackberry, Rubus pensilvanicus Poiret (= R. abactus Bailey), was collected in Humboldt County, CA. Although native to eastern North America, this host is an escaped cultivar that occurs in disturbed areas throughout California. Morphological and molecular data suggest that this rust is Phragmidium violaceum (Schultz) G. Winter. To confirm the identification of the specimen from California, an ~1,000-bp section of ribosomal DNA from the 28S large subunit was amplified and sequenced with rust-specific primers (M. C. Aime, unpublished data) (Genbank Accession No. EF672358). This sequence was 100% homologous to sequences of this rust species from Oregon and France. Widespread in Europe and introduced into Australasia as a biological control agent, P. violaceum has recently been reported from Oregon on Himalayan and evergreen blackberries, R. armeniacus Focke and R. laciniatus Willd. (2). Finding this rust in California about the same time as in Oregon suggests that its distribution may be widespread, possibly existing in the United States for some time. To our knowledge, this the first report from California and of the rust species on this plant host (1). The specimen from California is infected with urediniospores but lacks teliospores; it has been deposited at the U.S. National Fungus Collections as BPI 877816.
References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory. Online publication. USDA, ARS, 2007. (2) N. Osterbauer et al. Online publication. doi:10.1094/PHP-2005-0923-01-BR. Plant Health Progress, 2005.
