Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2006
Publication Date: 11/1/2006
Citation: Krupa, S., Bowersox, V.C., Claybrooke, R.D., Barnes, C.W., Szabo, L.J., Harlin, K.S., Kurle, J.E. 2006. Introduction of Asian Soybean Rust Urediniospores into the Midwestern United States – A Case Study. Plant Disease. 90:1254-1259. Interpretive Summary: The spread of Asian soybean rust (ASR) disease commonly occurs by the movement of fungal spores through the atmosphere. Long distance transport of fungal spores (wheat stem rust) is known to occur from the costal areas of the Gulf States to the upper Midwest. Deposition of the spores occurs primarily through rain. Particulate residue from rain samples collected weekly at 124 sites in the eastern and central U.S. were tested for ASR using a molecular assay specific for ASR fungal DNA. Rain samples collected during the week of 19 to 26 July, 2005 in Minnesota, Missouri and South Dakota tested positive for ASR fungal DNA. Analysis of weather patterns was used to trace back in time the path of the storms and identified southern Texas as the potential source areas from which the ASR fungal spores originated. In a second case study, ASR fungal DNA was detected in a rain sample from a site in eastern Texas (June 28 to July 5, 2005) and the analysis of the weather patterns indicated that the source area of the spores was from southern Texas and the Yucatan Peninsula in Mexico. This work demonstrated that the long distance movement of ASR fungal spores follows similar pathways for seasonal movement as other fungal rust spores. These results will be used by scientists to better understand the spread of ASR and may lead to improved predictive models to help farmers manage this disease.
Technical Abstract: In 2005, weekly rain samples collected at 124 National Atmospheric Deposition Program/National Trends Network (NADP/NTN) sites in the eastern and central United States were screened for Asian soybean rust (ASR; Phakopsora pachyrhizi) urediniospores. Application of a quantitative polymerase chain reaction method detected P. pachyrhizi DNA in the filter residue of these samples collected during the week of 19 to 26 July, 2005 in Minnesota, Missouri, and South Dakota. To determine the geographical origin of ARS urediniospores in those weekly composite samples, back air trajectories of the lifted condensation and mixed boundary layers were calculated for each rain event within the week, by sampling site. The calculations, based on the hybrid single-particle lagrangian integrated trajectory model, pointed to source areas in eastern and southern Texas. In a separate case, DNA of P. pachyrhizi was detected in a 28 June to 5 July, 2005 rain sample from an eastern Texas site. Back trajectories pointed to southern Texas and the Yucatan Peninsula in Mexico as potential source areas of ASR urediniospores. Vertical motions of those back trajectories indicated a ventilation of the boundary layer in these upwind areas, suggesting the possible injection of urediniospores into the free troposphere where they can be transported for long distances before wet deposition.