Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/7/2010
Publication Date: 6/8/2010
Citation: Haudenshield, J.S., Hartman, G.L. 2010. Archaeophytopathology of Global Soybean Rust. American Phytopathological Society North Central Division Annual Meeting, June 6-8, 2010, Rapid City, South Dakota, CD ROM.
Technical Abstract: Phakopsora pachyrhizi and P. meibomiae are two rust species that infect soybean (Glycine max). A number of other hosts support the uredinial growth of these Phakopsora, including Pachyrhizus erosus, Pueraria lobata, and Vigna unguiculata, but no aecial host is known. Traditionally, these two species are said to differ in geographic distribution, with P. pachyrhizi confined to Asia, Africa & Australia, and P. meibomiae confined to South & Central America. Several herbaria have accessions reported to contain one of the two species and include specimens from those locations, some nearly or over 100 years old. We sampled 38 of these archival specimens, and extracted & speciated the DNA of the fungus, if present, using quantitative PCR specific to either P. pachyrhizi, P. meibomiae, or to a third group inclusive of many rust species. Of the archival specimens, 11 were positive for P. pachyrhizi, including a 1912 specimen from Japan, but no P. pachyrhizi was found in specimens from before 1994 outside of Asia or Australia. Fifteen specimens were positive for P. meibomiae, including a 1928 specimen from Brazil and two 1923 specimens from the Philippines. Twelve specimens (including all African accessions) were found to be negative for both species, but six were positive in the more inclusive rust assay, and included specimens from Tanzania, Sao Tome, Nigeria, Sierra Leone, and China; all had been labeled as P. pachyrhizi and none were on G. max. These results demonstrate the feasibility of DNA genotyping in archaeophytopathological investigations and suggest that P. pachyrhizi may have been more recently introduced to Africa than previously believed.