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Asian soybean rust, caused by Phakopsora pachyrhizi Sydow, has been known to occur in the eastern hemisphere for nearly a century. More recently, it was reported from Hawaii in 1994, eastern and southern Africa from 1996-1998, Nigeria in 2001, and Brazil and Paraguay in 2002. Aerobiological models suggested that urediniospores of the pathogen would be disseminated on wind currents to the continental United States in association with tropical storms if the disease became established north of the equator during hurricane season (U.S. Soybean Rust Detection and Aerobiological Modeling online publication at www.aphis.usda.gov/ppq/ ep/soybean_rust/ ). Since soybean rust was observed at approximately 5°N latitude in South America before several hurricanes impacted the continental United States in September 2004, it seems likely that the introduction was associated with at least one of these tropical storms, especially hurricane Ivan. Symptoms of the disease were first observed on soybean (Glycine max (L.) Merr.) in the continental United States on November 6, 2004 in a field near Baton Rouge, LA. Typical pustules and urediniospores on infected leaves were readily apparent when viewed with a dissecting microscope. Urediniospores were obovoid to broadly ellipsoidal, hyaline to pale yellowish brown with a minutely echinulate thin wall, and measured 18 to 37 × 15 to 24 μm. Paraphyses were cylindric to clavate and slightly thickened at the apex, colorless to pale yellowish brown, and 25–50 × 6–14 μm in size. This morphology is typical of Phakopsora pachyrhizi and P. meibomiae, a less aggressive, western hemisphere species (2). DNA was extracted from leaves containing sori using the Qiagen DNeasy Plant Mini kit. P. pachyrhizi was detected using a real-time polymerase chain reaction (PCR) protocol (1) that differentiates between P. pachyrhizi and P. meibomiae performed in a Cepheid thermocycler with appropriate positive and negative controls. The PCR master mix was modified to include OmniMix beads (Cepheid). The field diagnosis of P. pachyrhizi was confirmed officially by the USDA/APHIS on November 10, 2004, and this was followed on November 11, 2004 by a wide-ranging survey of soybean and kudzu (Pueraria sp.) in soybean production areas in southern 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. To our knowledge, this is the first report of P. pachyrhizi in the continental United States. Voucher specimens have been placed in the USDA National Fungus Collection. References: (1) R. D. Frederick et al. Phytopathology 92:217, 2002. (2) Y. Ono et al. Mycol. Res. 96:825, 1992.

Asian soybean rust, caused by Phakopsora pachyrhizi Sydow, has been known to occur in the eastern hemisphere for nearly a century. More recently, it was reported from South America in 2002 and the continental United States in Louisiana in November 2004 (1,2). Subsequently, P. pachyrhizi was confirmed in Alabama, Arkansas, Georgia, Florida, Missouri, Mississippi, South Carolina, and Tennessee in 2004. Surveys conducted in North Carolina in late November 2004 failed to detect this pathogen. Symptoms of the disease were first observed on soybean (Glycine max (L.) Merr.) in North Carolina on 25 October 2005 in farmers' fields in the counties of Brunswick, Columbus, and Robeson. Typical pustules and urediniospores were readily apparent on infected leaves when viewed with a dissecting microscope. Urediniospores were obovoid to broadly ellipsoidal, hyaline to pale yellowish brown with a minutely echinulate thin wall, and measured 18 to 37 × 15 to 24 μm. This morphology is typical of soybean rust caused by P. pachyrhizi or P. meibomiae, the latter is a less aggressive species causing soybean rust in the western hemisphere (1). DNA was extracted from leaves containing sori using the Qiagen DNeasy Plant Mini kit (Valencia, CA). P. pachyrhizi was detected using a real-time polymerase chain reaction (PCR) protocol that differentiates between P. pachyrhizi and P. meibomiae in a Cepheid thermocycler (Sunnyvale, CA) with appropriate positive and negative controls. The PCR master mix was modified to include OmniMix beads (Cepheid). Field diagnosis of P. pachyrhizi was confirmed by the USDA/APHIS on 28 October 2005. Soybean rust was identified in subsequent surveys of soybean fields and leaf samples submitted by North Carolina Cooperative Extension Agents in an additional 15 counties. These samples also were assayed using a traditional PCR protocol and by the enzyme-linked immunosorbent assay protocol included in the EnviroLogix QualiPlate kit (Portland, ME) for soybean rust. Ten soybean specimens from 10 sites were confirmed positive by these methods. Disease was not found on three kudzu samples, although one kudzu sample was adjacent to a soybean field that was positive for P. pachyrhizi. Although soybean rust was eventually detected in 18 North Carolina counties in 2005, no soybean yield loss occurred since the pathogen was detected when more than 80% of the soybean crop was mature. To our knowledge, this is the first report of P. pachyrhizi in North Carolina and the northern most find on soybean in the continental United States in 2005. References: (1) R. D. Frederick et al. Phytopathology 92:217, 2002. (2) R. W. Schneider et al. Plant Dis. 89:774 2005.