THE POTENTIAL FOR SPREAD OF ERWINIA-AMYLOVORA AND FIRE BLIGHT VIA COMMERCIAL APPLE FRUIT - A CRITICAL-REVIEW AND RISK ASSESSMENT

The biology of Erwinia amylovora is reviewed with reference to the phy tosanitary risk associated with the movement of export-quality apple f ruit to countries where fire blight does not occur or is not widely es tablished. The low epiphytic fitness of E. amylovora on apple fruit, t he low incidence of viable E. amylovora populations on mature apple fr uit, and the lack of a documented pathway by which susceptible host ma terial could become inoculated and infected from fruit-borne inoculum all support the view that movement of E. amylovora via commercial appl e fruit is highly unlikely. A simple linear model using published data for estimation of fruit contamination levels was used to estimate the likelihood of fire blight outbreaks in unaffected areas as a result o f commercial fruit shipment. We estimate the likelihood of a new outbr eak of fire blight in a previously blight-free area caused by movement of E. amylovora on commercial apple fruit to be one outbreak every 38 462 years under the current (United States and New Zealand) apple exp ort programs for Japan. Under a 'relaxed' program without buffer zones , with one preharvest orchard inspection and allowing a low incidence of fire blight in export orchards, one outbreak in 35 971 years may oc cur. If fruit were to be exported from any area, one outbreak in 11 36 4 years may occur. By using the published data and making assumptions based upon documented pathogen biology, the model indicates that the r isk of importing E. amylovora on commercial apple fruit and the concom itant risk of establishing new outbreaks of fire blight is so small as to be insignificant. Published by Elsevier Science Ltd.