First Report of Phakopsora pachyrhizi, the Causal Agent of Asian Soybean Rust, on Florida Beggarweed in the United States

Abstract

Phakopsora pachyrhizi Syd. & P. Syd., which causes Asian soybean rust (SBR), was observed on Florida beggarweed, Desmodium tortuosum (Sw) DC., in Attapulgus, GA during late October and early November 2005. Tan to brown lesions (<1.0 mm in diameter) consistent with symptoms of SBR (2) were observed on older leaves of several plants collected near an SBR-infected soybean trial. Dissection (40 to 60×) and compound microscopy (×200 to 400) revealed conical pustules and ellipsoid, echinulate urediniospores (average size 15 × 20 μm) on the abaxial leaf surface. Polymerase chain reaction (PCR) (primers Ppm1 and Ppa2) (1) was conducted on four samples to confirm identification of P. pachyrhizi or P. meibomiae. Three were positive for P. pachyrhizi, and one was negative for both species. Using morphology and real-time PCR, SBR was confirmed as P. pachyrhizi by the USDA/APHIS in Beltsville, MD. Six noninfected Florida beggarweed plants were transplanted to pots during December 2005 and grown at 22 to 24°C in a greenhouse. On 11 January 2006, a water suspension of urediniospores collected from SBR-infected soybeans (1 × 105 spores per ml) was spray inoculated on all leaves to almost runoff and incubated for 48 h in a plastic humidity chamber. Lesions, pustules, and urediniospores consistent with SBR (2) were observed on 3 February 2006. A PCR assay was conducted on six samples from the infected greenhouse plants and all were positive for P. pachyrhizi. Florida beggarweed is widespread in the southern United States and may serve as an additional overwintering source for P. pachyrhizi and a potential inoculum source for the soybean crop. References: (1) R. D. Fredrick et al. Phytopathology 92:217, 2002. (2) J. B. Sinclair and G. L. Hartman. Soybean rust. Pages 25–26 in: Compendium of Soybean Diseases. 4th ed. G. L. Hartman et al., eds. The American Phytopathological Society, St. Paul, MN, 1999.

Soybean production in eastern and southern Africa and threat of yield loss due to soybean rust caused byPhakopsora pachyrhizi

“…Phakopsora pachyrhizi has an exceptionally broad host range, comprising more than 150 species in about 53 genera of the legume family, the largest family of flowering plants (Ono et al, 1992;Hartman et al, 2011a). Wild hosts include kudzu (Pueraria lobata) and beggar weed (Desmodium tortuosum) (Isakeit et al, 2006;Sconyers et al, 2006). Common cultivated legumes that serve as hosts include Phaseolus vulgaris (common bean), Phaseolus coccineus (scarlet runner bean), Vigna unguiculata (cowpea), Cajanus cajan (pigeon pea), Pisum sativum (field pea), Lens culinaris (lentil) and the fodder legume Neonotonia wightii (Lynch et al, 2006;Nunkumar et al, 2008).…”

A Coordinated Effort to Manage Soybean Rust in North America: A Success Story in Soybean Disease Monitoring

“…3), coral bean (Erythrina herbacea L.), and Florida beggarweed (Desmodium tortuosum (Sw) DC.) (11,17,62) (Sidebar 2: Kudzu in the city: Soybean rust overwintering in urban environments). For a complete list of currently recognized hosts of P. pachyrhizi, see Rytter et al (59), and Slaminko et al (66,67).…”

Identification of Unique Genetic Sources of Soybean Rust Resistance from the USDA Soybean Germplasm Collection

“…Kudzu [Pueraria lobata (Willd.) In the United States, it has also been reported on Florida beggarweed (Desmodium tortuosum) in both Georgia and Alabama, so that species could be an additional overwintering host for SBR (Delaney et al, 2012;Sconyers et al, 2006). However, the pathogen has been reported to occur on more than 150 legume species worldwide (Sinclair and Hartman, 1999;Slaminko et al, 2008).…”

“…However, the pathogen has been reported to occur on more than 150 legume species worldwide (Sinclair and Hartman, 1999;Slaminko et al, 2008). In the United States, it has also been reported on Florida beggarweed (Desmodium tortuosum) in both Georgia and Alabama, so that species could be an additional overwintering host for SBR (Delaney et al, 2012;Sconyers et al, 2006).…”