Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 19, 2007
Publication Date: November 2, 2007
Citation: Aime, M.C., Rossman, A.Y. 2007. First report of the rust Phragmidium violaceum on Pennsylvania blackberry in California. Plant Disease. 91:1517.
Interpretive Summary: Rust fungi are a very large and diverse group of parasites that attack crop and forest plants. Accurate knowledge of the distribution of rust fungi is important for tracking the movement of these disease-causing fungi. In this research a rust fungus that infects blackberries and related hosts was discovered for the first time in the California. It had only recently been reported for the first time in the United States from Oregon but appears to have already spread. Knowledge of the distribution of plant pathogenic fungi is useful to agronomists and plant pathologists as well as plant regulatory and quarantine officials.
In April 2005 a rust fungus was collected on Pennsylvania blackberry, Rubus pensilvanicus Poiret (= R. abactus Bailey) in Humboldt Co., California. Both morphological and molecular data suggest that this rust is Phragmidium violaceum (Schultz) G. Winter. Although this host is native to eastern North America, it occurs in disturbed areas throughout most of California and is considered an escaped cultivar. Phragmidium violaceum has recently been reported from Oregon on Himalayan and evergreen blackberries, Rubus armeniacus Focke and R. laciniatus Willd. (2). To confirm the identification of the specimen from California, an ~1,000 bp section of ribosomal DNA from the ribosomal 28S large subunit was amplified and sequenced with rust-specific primers (Aime, unpublished) (Genbank Acession No. EF672358). This sequence was 100% homologous to sequences of this rust species from Oregon and France. Finding this rust in California at same time that it was noticed in Oregon suggests that its distribution is more widespread in the United States than had been previously known. In addition to being the first report from California, this appears to be the first report 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.