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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVED RESISTANCE TO SOYBEAN PATHOGENS AND PESTS

Location: Soybean/maize Germplasm, Pathology, and Genetics Research

Title: First report of Soybean Rust (Phakopsora pachyrhizi) on Florida Beggarweed (Desmodium tortuosum) in Alabama

Authors
item Delaney, M -
item Sikora, E -
item Delaney, D -
item Palm, M -
item Haudenshield, James
item Hartman, Glen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 29, 2012
Publication Date: September 1, 2012
Citation: Delaney, M.A., Sikora, E.J., Delaney, D.P., Palm, M.E., Haudenshield, J.S., Hartman, G.L. 2012. First report of Soybean Rust (Phakopsora pachyrhizi) on Florida Beggarweed (Desmodium tortuosum) in Alabama. Plant Disease. 96(9):1374.

Interpretive Summary: Soybean rust, caused by the fungus Phakopsora pachyrhizi, was detected on Florida beggarweed (Desmodium tortuosum) for the first time in Alabama in November, 2009. The pathogen was not observed in 2010 or 2011, probably because of the exceptionally dry, hot weather in the region. The pathogen was observed on multiple mature leaves of plants, evenly distributed through a field at the Wiregrass Research and Extension Center in Headland, Alabama, located in the southeast region of the state. Symptoms on leaves were consistent with soybean rust symptoms previously described on soybean. The identification of the fungus was confirmed using immunological and molecular techniques. Florida beggarweed is one of the most troublesome weeds in the southeastern U.S. The ability of P. pachyrhizi to reproduce on Florida beggarweed provides the fungus a host that could allow it to persist in environments when soybean plants are not available. This information will be useful to scientists and soybean producers who are interested in the epidemiology and management of soybean rust.

Technical Abstract: Soybean rust (SBR), caused by the fungus Phakopsora pachyrhizi, was detected on Florida Beggarweed (Desmodium tortuosum) for the first time in Alabama in November, 2009. The pathogen was not observed in 2010 or 2011, probably because of the exceptionally dry, hot weather in the region. The pathogen was observed on multiple mature leaves of plants, evenly distributed through a field at the Wiregrass Research and Extension Center in Headland, Alabama, located in the southeast region of the state. Florida Beggarweed can serve as an overwintering host for SBR. Symptoms on leaves were consistent with SBR symptoms previously described on soybeans (1). Sori in multiple pustules were observed on the undersurface of the leaves. Urediniospores and paraphyses were observed microscopically and identified as P. pachyrhizi. Symptomatic leaves from 20 plants were analyzed using an Envirologix monoclonal antibody strip test kit at the Auburn University Plant Diagnostic Laboratory. A subsample of 20 plants were positive for the pathogen. Representative symptomatic leaves were sent to the USDA Molecular Diagnostic Laboratory in Beltsville, Maryland, for confirmation. DNA was extracted from sori aseptically removed from leaves using a Qiagen DNeasy Plant Mini Kit, and amplified with primers Ppa1 and NL4. The resulting partial ITS2 and 28S ribosomal RNA sequences were 100% identical to GenBank entry DQ354537. Voucher specimens were deposited in the USDA Agricultural Research Service, National Fungus Collection (BPI). To our knowledge, this is the first report of the disease on Florida Beggarweed in Alabama.

Last Modified: 7/28/2014
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