Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/6/2009
Publication Date: 5/15/2009
Citation: Peterson, G.L., Whitaker, T.B., Stefanski, R.J., Pedleckis, E.V., Phillips, J.G., Wu, J.S., Martinez, W.H. 2009. A Risk Assessment Model for Importation of U.S. Wheat Containing Telletia controversa. Plant Disease. 93:560-573. Interpretive Summary: Dwarf bunt of wheat, caused by the fungus Tilletia controversa Kuhn (TCK), is a pathogen historically limited in distribution by its very specific environmental requirements for establishment. A number of U.S trading partners established trade barriers to U.S wheat exports over of concerns of introducing this wheat disease into their country. Utilizing both the historical scientific literature and newly conducted studies, a quantitative risk assessment model was developed to communicate the risk associated with the importation of U.S. milling wheat containing teliospores of the dwarf bunt pathogen. The TCK-Risk model quantitatively evaluates the possible pathways of teliospore escape from export terminal to milling, the probability that spores will arrive in a wheat field in sufficient numbers to cause disease, and determines if the climatic condition are conducive to the establishment and spread of the disease. Data used in the model are contained in distributions (e.g. number of TCK spores in individual shipments over a 6-year period, or tons of wheat imported by a trading partner over 10 or more years) which allows for the use of simulations to examine the effects of changes in the pathway variables. The TCK risk model was applied to Brazil, Mexico, Peru and China. Results suggest climatic conditions in Mexico, Brazil and Peru would not support the introduction and establish of dwarf bunt. In China, areas favorable for disease development, where identified, however these locations were far from any wheat import terminal or major milling facility. Conclusions from the risk model suggested that the likelihood of teliospores escaping the milling process and arriving in a wheat field in those disease conducive regions was highly unlikely.
Technical Abstract: Dwarf bunt of wheat, caused by the fungus Tilletia controversa Kuhn (TCK), is a pathogen historically limited in distribution by its very specific environmental requirements for establishment. In an effort to both address the need for adequate phytosanitary protection, and to eliminate unwarranted trade barriers, a number of countries have examined restrictions on importing milling-wheat containing teliospores of TCK. Pest Risk Analysis (PRA), under the guidelines of the World Trade Organization and Food and Agriculture Organization, has become an internationally accepted process for evaluating such issues. As a component of a TCK PRA, our objective was to develop a quantitative TCK risk-assessment model to evaluate and communicate the potential risk of introduction, establishment and yield loss from the importation of U.S. milling-wheat containing teliospores of TCK. A TCK-PRA model was developed by a multi-national task force using new, historic and estimated data expressed as distributions. These distributions were utilized in Monte Carlo simulations to quantify risk. The TCK-PRA model examines pathways of teliospore diversion from transport and milling processes, spore contamination levels, grain handling, and end-product usage. A geophytopathological model (GM) was developed to identify regions of potential risk using weather data from the widely available United Nations, World Meteorological Organization’s telecommunications network. When the GM model was applied to the U.S., results correlated well with the known distribution of the disease. TCK-PRA model evaluation scenarios for Peoples Republic of China, Brazil, Mexico and Peru were conducted and presented.