Submitted to: Crop Protection Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 2, 2007
Publication Date: March 1, 2008
Citation: Roberts, R.G., Sawyer, A.J. 2008. An updated pest risk assessment for spread of erwinia amylovora and fire blight via commercial apple fruit. Crop Protection Journal. 27:362-368. Interpretive Summary: International trade in apple fruit from countries with fire blight disease to countries without the disease has been slowed or prevented by very restrictive plant quarantine regulations implemented by importing countries. Although the U.S. recently prevailed against Japan’s unnecessarily restrictive regulations in a WTO dispute, some countries such as Australia still maintain similar or even more restrictive regulations. This paper updates a quantitative pest risk assessment for fire blight disease spread via apple fruit originally published in 1998 with new and corrected information that has become available since 1998. With this new information included in the model, the estimations for the number of years before the first expected outbreak of fire blight because of international apple shipment increased dramatically, indicating that the risk of spreading fire blight by apple fruit is even lower than the extremely low likelihood previously published. Although the model is still extremely conservative in that it overestimates the risk, the estimated time before the first outbreak of fire blight disease in a previously fire blight free country due to importation of apple fruit from a country with fire blight ranged from 5,217 years to 753,144 years.
Technical Abstract: The phytosanitary risk associated with the movement of export-quality apple fruit to countries where fire blight does not occur is reassessed based upon additional data available since 1998 and clarification or correction of previously misinterpreted data present in the literature. The low epiphytic fitness of Ea on apple fruit, the documented low incidence of viable Ea populations on mature apple fruit and the lack of a documented pathway by which susceptible host material could become infected from fruit-borne inoculum remain unchanged, and support the view that movement of Ea via commercial apple fruit is highly unlikely. With this new information, we updated a previously published model to re-estimate the likelihood of fire blight outbreaks in new areas because of commercial fruit shipment. This likelihood decreased in every scenario, and ranged from one outbreak in 5,217 years to one in 753,144 years. By using the corrected and newly published data and by making assumptions based upon documented pathogen biology, the model gives more robust statistical support to the opinion that the risk of importing Ea on commercial apple fruit and the concomitant risk of establishing new outbreaks of fire blight is so small as to be insignificant.