Submitted to: Association of Analytical Committees
Publication Type: Abstract Only
Publication Acceptance Date: 9/14/2003
Publication Date: 9/14/2003
Citation: Peterson, G.L., Whitaker, T.B. 2003. Uncertainty of sampling for dwarf bunt (tck) spores in wheat. Association of Analytical Committees. Abstracts of the 117th Annual Meeting of Official Analytical Chemists. September, 2003. Atlanta, GA Interpretive Summary:
Technical Abstract: In 1999, the U.S/China Agricultural Cooperative Agreement (ACA) was signed which ended a 25-year embargo of U.S. wheat exports from the Pacific Northwest caused by the presence of fungal spores of TCK (Tilletia controversa Kuhn). The agreement established a tolerance level of 30,000 TCK spores per 50-g test sample in U.S. wheat exports to China. The foundation of this agreement was an extensive ARS research program that culminated in the development of a TCK Pest Risk Assessment (PRA) model for the importation of TCK-affected wheat. An important aspect of the model was to develop a method for estimating the total numbers of spores in a U.S. export shipment based on a single-ship 50-g composite wheat sample taken at loading. In our study, 1-kg whole-ship wheat composite samples, representing a range of TCK contamination levels, were taken from 137 export shipments. For each 1-kg sample, sixteen 50-g sub-samples were tested. It was found that the standard deviation among the 16 sub-samples increased with TCK concentration. However, increasing the sample volume or testing multiple samples could significantly reduce the variability associated with a single 50-g sample. These data provided the statistical basis for estimating TCK teliospore contamination levels and the issuance of an export certification indicating that the number of TCK spores was within the TCK tolerance level negotiated in the ACA. Furthermore, these data in conjunction with 50-g test sample results from over 10,000 export ships were utilized in the development of statistically based operating characteristic curves that clearly communicated to trading partners both the importer's and exporter's risks associated with the application of these testing methods for certification of U.S. wheat exports to China.