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Modeling the Risk of Entry, Establishment, Spread, Containment, and Economic Impact of Tilletia indica, the Cause of Karnal Bunt of Wheat, Using an Australian Context

First author: Department of Agriculture Western Australia, Bunbury District Office, P.O. Box 1231, Bunbury 6231 Western Australia, Australia; second and third authors: Department of Agriculture Western Australia, South Perth Office, Locked Bag No. 4, Bentley Delivery Centre 6983 Western Australia, Australia; and fourth author: Applied and Molecular Ecology, University of Adelaide, Waite Campus, PMB1, Glen Osmond 5064 South Australia, Australia

Modeling techniques were developed to quantify the probability of Tilletia indica entering and establishing in Western Australia (WA), and to simulate spread, containment, and the economic impact of the pathogen. Entry of T. indica is most likely to occur through imports of bulk grain or fertilizer (0.023 ± 0.017 entries per year and approximately 0.009 ± 0.009 establishments per year). Entry may also occur through straw goods, new or second-hand agricultural machinery, and on personal effects of travelers who have visited regions with infected plants. The combined probability of entry and establishment of T. indica, for all pathways of entry, is about one entry every 25 years and one establishment every 67 years. Alternatively, sensitivity analysis does show that increases in quarantine funding can reduce the probability of entry to about one entry every 50 years and less than one establishment every 100 years. T. indica is spread efficiently through contaminated farm machinery, seed and soil, rain, air currents, and animals. Depending on the rate of spread of the pathogen and the amount of resources allocated for detection, the time until first detection could range from 4 to 11 years and the economic impact could range from 8 to 24% of the total value of wheat production in WA.

Additional keywords: area freedom, import risk analysis, quantitative risk assessment, quarantine.