Submitted to: Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/6/2001
Publication Date: 11/1/2001
Citation: WHITAKER, T.B., WU, J.S., PEDERSON, G.A., GIESBRECHT, F.G., JOHANSSON, A.S. INSPECTING WHEAT SHIPMENTS FOR TILLETIA CONTROVERSA KUHN SPORES, PART I: VARIABILITY AMONG SAMPLE TEST RESULTS. PLANT PATHOLOGY. 2001. v. 30. p. 755-760. Interpretive Summary: Dwarf bunt is caused by a fungus, Tilletia controversa Kuhn, that infects wheat under certain environmental conditions and can reduce wheat yields. About 15 countries have import restrictions on U.S. wheat containing spores of T. controversa, which creates a severe economic burden on U.S. wheat producers and exporters. Several countries have recently lifted import restrictions or placed acceptable tolerance levels for T. controversa spores in imported wheat. Precise measurements of these spores in wheat shipments is very important when a country establishes a regulatory tolerance. It is difficult to determine the exact levels of contamination in a large wheat shipment because of the errors associated with the sampling procedure. Errors in the sampling procedure results in some lots being misclassified. Some of the good lots test bad and some of the bad lots test good. The errors associated with sampling wheat for T. controversa spores were determined. Knowing the magnitude of the sampling errors will help develop cost-effective methods to reduce sampling errors and reduce the number of lots misclassified. This will reduce economic losses for both the exporter and the importer of wheat shipments.
Technical Abstract: The variability associated with estimating the true number of Tilletia controversa Kuhn spores per 50 g of wheat (TCK concentration) in an export wheat shipment was studied by measuring the TCK concentration in sixteen 50-g test samples taken from each of 137 export shipments. The variability among the 16 TCK test sample results, as measured by the standard deviation nwas found to increase with TCK concentration. The functional relationship was approximately linear in a full-log plot and regression analysis was used to determine the coefficients of the regression equation. Using statistical theory, the regression equation was modified to predict the standard deviation associated with different test sample sizes other than the 50-g size used in this study. The standard deviation and coefficient of variation associated with using a 50-g test sample to estimate the true TCK concentration of a wheat shipment with 2000 spores/50 g was estimated to be 722.3 and 36.1 percent, respectively. Increasing test sample size to 1600 g reduced the standard deviation to 127.7.