ARS | Publication request: 2005: INTRODUCTION AND SPREAD OF SOYBEAN RUST SPORES IN THE NORTH CENTRAL UNITED STATES

Submitted to: APS Net Plant Pathology Online
Publication Type: Abstract Only
Publication Acceptance Date: November 1, 2005
Publication Date: December 1, 2005
Citation: Kurle, J., Bowersox, V., Claybrooke, R., Krupa, S.V., Barnes, C.W., Szabo, L.J. 2005. 2005: introduction and spread of soybean rust spores in the north central united states. Available: http://www.plantmanagementnetwork.org.

Technical Abstract: In 2004 the USDA issued its first report of Asian soybean rust (ASR, Phakopsora pachyrhizi) in the continental U.S. Survival and dispersal of ASR is dependent on continuous production of urediniospores. It cannot survive typical U.S. winters, except perhaps in southernmost Texas and Florida, Gulf Coast States, and southern California. Rusts of small grains, which do not survive freezing, are re-introduced to the northern U.S. from inoculum sources in Mexico, southern Texas, and Louisiana. Long-range transport and deposition of viable spores from these areas is an important mechanism for reintroducing cereal rusts annually and is a postulated mechanism for dispersal of P. pachyrhizi spores to northern U.S. States. Rain is the dominant mechanism for depositing spores carried in winds for hundreds or thousands of km from the source regions. Nested qPCR was used to detect DNA of P. pachyrhizi in filter residue of rain samples collected at 124 National Atmospheric Deposition (NADP) sites. Rain samples were vacuum-filtered, and the filters dried, sealed in Petri dishes, and sent for qPCR analysis to the USDA-ARS Cereal Disease Laboratory in St. Paul, MN. Samples from two sites in South Dakota and one in Minnesota tested positive for P. pachyrhizi DNA during 19-26 July 2005. For rain events during this period at these sites, back trajectories of the cloud and boundary layers were calculated using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, to represent in-cloud and below-cloud scavenging of ASR spores. Results point to a source area in southern Texas not previously identified.