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Title: FIRST REPORT OF SOYBEAN RUST CAUSED BY PHAKOPSORA PACHYRHIZI IN THE CONTINENTAL UNITED STATES

Author
item SCHNEIDER, W - LA STATE U. BATON ROUGE
item HOLLIER, C - LA STATE U. BATON ROUGE
item WHITAM, H - LA STATE U. BATON ROUGE
item PALM, M - USDA APHIS, BELTSVL, MD
item MCKEMY, J - USDA APHIS, BELTSVL, MD
item Hernandez, Jose
item LEVY, L - USDA APHIS BELTSVL, MD
item DEVRIES-PATERSON, R - USDA APHIS, BELTSVL, MD

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2005
Publication Date: 6/10/2005
Citation: Schneider, W., Hollier, C.A., Whitam, H.K., Palm, M.E., Mckemy, J.M., Hernandez, J., Levy, L., Devries-Paterson, R. 2005. First report of soybean rust caused by Phakopsora pachyrhizi in the continental United States. Plant Disease. 89:774.

Interpretive Summary: Soybean rust is a fungus that has been considered a threat to the United States for at least two decades. Once this disease moved from Africa to South America, scientists predicted that soybean rust could be blown northward into the U.S. by hurricane winds. This research reports the discovery of soybean rust in fields in Louisiana in November, 2004. It is speculated that teliospores of the fungus were moved into the U.S. with Hurricane Ivan in September, 2004. The accurate identity of the fungus causing this disease was confirmed by both morphological and molecular examination. A search for the fungus revealed that it was present in five sites in the southeastern United States. This research will be used to stimulate the development of plans to control and manage soybean rust in the United States.

Technical Abstract: Asian soybean rust, caused by Phakopsora pachyrhizi has been present in the eastern hemisphere for nearly a century. More recently it was reported from Hawaii, East and South Africa, Nigeria, and Brazil and Paraguay in 2002. Aerobiological models suggested that urediniospores of the pathogen would be disseminated on wind currents to the continental U.S. in association with tropical storms if the disease became established north of the Equator during hurricane season. This situation occurred in September 2004 when soybean rust was confirmed at about 5 degrees north latitude, and several hurricanes, especially Hurricane Ivan. Symptoms of the disease were first observed on soybean (Glycine max [L.] Merr.) in the continental U.S. on November 6, 2004 in a field near Baton Rouge, Louisiana. Typical pustules and urediniospores on infected leaves were readily apparent when viewed with a dissecting microscope. On November 8, 2004 leaf specimens were sent via overnight mail to the USDA/APHIS laboratory in Beltsville, Maryland for confirmation. At the NPGBL, DNA was extracted from leaves and P. pachyrhizi was detected using a real-time PCR protocol. The field diagnosis of P. pachyrhizi was confirmed officially by APHIS on November 10, 2004, and this was followed on November 11, 2004 by a wide-ranging survey of soybean and kudzu in soybean production areas in south and central Louisiana. Collections from this survey also were assayed as described above, and six soybean specimens from five sites were confirmed positive. The disease was not found on kudzu samples. This is the first report of P. pachyrhizi in the continental United States.