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Title: First Report of Garlic Rust Caused by Puccinia allii on Allium sativum in Minnesota

item Szabo, Les
item MOLLOV, DIMITRI - University Of Minnesota
item ROSEN, CARL - University Of Minnesota

Submitted to: Disease Note
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2012
Publication Date: 2/1/2013
Citation: Szabo, L.J., Mollov, D.S., Rosen, C. 2013. First Report of Garlic Rust Caused by Puccinia allii on Allium sativum in Minnesota. Disease Note. 97(2):285.2.

Interpretive Summary: High-quality garlic is an important emerging crop for small farmers in Minnesota. The recent discovery of garlic rust may have a negative impact on the profitability of this crop. ARS scientists in St. Paul, along with collaboration with scientist's at the University of Minnesota, analyzed infected garlic plants and determined that the disease was caused by the fungal pathogen Puccinia allii. Two distinct types of P. allii are known, "garlic type" and "leek type" of this pathogen. By examining morphological characters of the fungal spores and DNA sequence analysis it was determined that this sample was of the "garlic type". This represents the first report of garlic rust pathogen in Minnesota, and raises the concern of this disease spreading in the United States. Occurrence of garlic and leek rust in the United States has been rare, until an outbreak of garlic rust in California in the late 1990s, which lead to elimination of the garlic crop. Recently, leek rust has become a serious problem in California. Agricultural professionals and scientists will use results from this research.

Technical Abstract: In July 2010, Allium sativum, cultivar German Extra Hardy Porcelain plants showing foliar symptoms typical of rust infection were brought to the Plant Disease Clinic at the University of Minnesota by a commercial grower from Fillmore county Minnesota. Infected leaves showed circular to oblong lesions (1-3 mm long), which ranged in color from yellow-orange (uredinia) to black (telia). Urediniospores collected from uredinia were globoid to ellipsoid, yellowish in color, and measured 18 ¬+ 1 µm x 30 + 2 µm with a wall thickness of 2.4 + 0.5 µm. Teliospores were two celled, measured 18 + 3 µm x 47 + 10 µm with a cross sectional area of 826 + 87 µm2; cell walls were smooth, brown in color, and 1.6 + 0.3 µm (proximal cell) to 2.1 + 0.5 µm (distal cell) thick and 4.2 + 0.8 µm at the apex. The pathogen was identified as Puccinia allii (1) and a sample was deposited in the U.S. National Fungus Collection (BPI 884132). DNA was extracted from infected leaf tissue and the nuclear ribosomal Internal Transcribed Spacer region (ITS) and 5’ end of the large subunit (LS) was amplified and sequenced as described by Anikster et al (2). The 1,257 bp sequence from the sample collected in Minnesota (GenBank Accession No. JX402206) was identical to ITS/LS sequence of a sample of P. allii collected from garlic in California (GenBank accession no. AF511077) with the exception of that MN sequence contained nine “A”s rather than 10 in the hyper-variable area at the 3’ end of the ITS region. P. allii has been shown to be a species complex comprising of at least two different types; ‘leek type’ and ‘garlic type’ (2). Based on the ITS sequence and the cross sectional area of the teliospores the sample of P. allii from MN, is consistent with the ‘garlic type’. High-quality garlic is an emerging crop grown in Minnesota for local markets, community supported agriculture, and select restaurants.