Tomato field destroyed by late blight (Phytophthora infestans).
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enlargement and more information

Bacterial canker of tomato caused by Clavibacter michiganensis pv michiganensis.
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enlargement and more information.

In his symposium presentation on epidemiology and risk prediction, Dr. L. V. Madden unveiled a probabilistic model for assessing the risk of crop bioterrorism (Dr. L. V. Madden, "Epidemiology and risk prediction," see abstract). The model includes the probability of introduction, initial establishment, disease spread, and control. If asked to list the top 10 candidate plant pathogens with high risk potential for deliberate introduction, most plant pathologists would probably list those pathogens with which they are most familiar and have historically caused severe crop losses in the past. Because a deliberate introduction may involve non-traditional agents or modified agents and might not follow historical trends, such a decision based on personal experience and history may very well be misleading. A better approach is to develop criteria and a numerical rating system or "Effective Pathogen Index" (EPI) to assess risk and probability of harm (N. W. Schaad, "What is an effective pathogen?" (see abstract). A criteria and a numerical score such as the following could be developed:

Possible Bioterrorist Pathogen Rating Criteria and Points

! Produces toxin 15
! Easy to obtain, handle, and deliver 10
! Easy to grow in large amounts 10
! Highly infectious under many conditions 10
! Results in the establishment of a quarantine 10
! No chemical control or host resistance available 10
! No method for rapid or reliable detection 10
! Infects systemically by natural means 10
! Spreads quickly by natural means 5
! Causes severe crop losses 5
! Survives long periods and is persistent 5

A perfect organism would have a EPI of 10 (for example, add the total points and divide by 10). Similar criteria for a BW agent as part of a state supported BW program could be developed. These criteria could include many of the above plus points for ease of genetic manipulation.

To prepare our agricultural system to withstand a deliberate release of a plant pathogen, a serious evaluation of the appropriate threat agents must be performed. As stated by Dr. R. Hickson ("Subtle forms of strategic indirect warfare: infecting "soft" biological targets; some psychological, economic, and cultural consequences," see abstract) the psychological, economic, and cultural consequences of crop bioterrorism, especially attacks on such soft targets as crop seeds, could have a disproportionally adverse effect on our agriculture and society.


We urge all relevant agencies, to recognize the need to confront this threat and financially support appropriate research for fingerprinting high priority pathogens, detecting deliberate releases, developing rapid genetic-based diagnostic assays, epidemiology and risk prediction, and other scientific and technical approaches to reduce this risk. It is hoped that this article will stimulate further discussion of this topic.

Topics on crop biosecurity that need to be explored include the following:

  • Awareness of the problem
  • Involvement among plant pathologists
  • Collaboration among government agencies, the commercial sector, international organizations, and universities
  • Funding for all aspects of plant pathology research of significance to crop biosecurity, especially on molecular characterization and detection and identification of plant pathogens, and air and ground surveillance instrumentation

Additionally, training in these areas is much needed for those with responsibilities and interest in all sectors of crop agriculture including pathology extension specialists, students, crop consultants, federal and state regulators, and farm advisors at various levels.

Discussion topics

The APS has sponsored a web site for further discussion of the issues raised herein.  Click the link titled in the top left margin titled "Discussion Area." Interested readers are urged to examine the comments posted by others and to post their own thoughts and ideas for the plant pathology community.

Literature cited

1. Alibek, K. and S. Hanelman. 1999. Biohazard: The Chilling True Story of the Largest Covert Biological Weapons Program in the World-Told from the Inside by the Man Who Ran It. Random House. (ISBN: 0375502319) 336 pp.

2. Damsteegt, V. D. 1999. New and emerging plant viruses. APSnet, August 1 to 31.

3. Henderson, D. A. 1998. Bioterrorism as a public health threat. Emerging Infectious Diseases (Special Issue) 4:488-492.

4. Kay, B. A., R. J. Timperi, S. S. Morse, D. Forslund, J. J. McGowan and T. O'Brien. 1998. Innovative information-sharing strategies. Emerging Infectious Diseases (Special Issue) 4:465-466.

5. McDade, J. E. and D. Franz. 1998. Bioterrorism as a public health threat. Emerging Infectious Diseases (Special Issue) 4:493-494. (

6. Rogers, P., S. Whitby, and M. Dando. 1999. Biological warfare against crops. Sci. Am. 280:70-75.

7. Weller, R. E., C. W. Lyu, C. Wolters, and R. M. Atlas. 1999. Universities and the biological and toxin weapons convention. ASM News 65:403-409.

8. Whitby, S. and P. Rogers. 1997. Anticrop biological warfare-implications of the Iraqi and U.S. programs. Defense Analysis 13:303-318.  

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