stereotyping GMPP plants had some predictive power, but later investigators found that there were too many exceptions (Lamberti et al. 1981). Durability of a specific GMPP plant is now typically judged in retrospect on the basis of its long term performance (Johnson 1981).

There have been some recent attempts to use population-genetics theory for developing and deploying conventional pest-protected plants in ways that slow pathogen adaptation (Burdon et al. 1994; Lannou and Mundt 1996 and 1997; Mundt 1990; Zeigler 1998), but it has not become common practice. Instead, many current pathology programs for production of GMPP plants emphasize continual discovery of new resistance genes so that breeding programs can stay a step ahead of an evolving pathogen (McIntosh and Brown 1997).

Researchers developing engineered pathogen-resistant plants have also been concerned with pest adaptation (Beachy 1997). Although new molecular approaches could lead to plants that offer a greater evolutionary challenge to pathogens (Beachy 1997; Bendahmane et al. 1997), little empirical or theoretical work has been aimed at determining how to produce durable engineered pathogen resistance (but see Qiu and Moyer 1999).

2.9.3 Future of Resistance Management for GMPP Plants

EPA has been active in developing resistance management plans for Bt crops. It has developed an internal group of staff to work on the issue and has consulted formally and informally with researchers (Matten et al. 1996; Matten 1998). Researchers and EPA regulatory officials will probably learn a lot of general principles about how to develop and implement resistance management of transgenic pest-protected plants from the continuing work on Bt crops. Much has already been learned from the Bt system regarding theoretical and practical aspects of developing and implementing a resistance management program, but the EPA policy is still evolving (Matten 1998). Each year, new empirical results should provide information on better ways to optimize resistance management for these crops. Therefore, plans implemented today will need to be periodically reviewed for their continued usefulness.

Although EPA has instituted programs and regulations that demonstrate serious concern about insect adaptation to Bt crops (Matten 1998; SAP 1998), it has not indicated concern about virus adaptation to transgenic pest-protected plants with plant-produced viral coat protein. In general, EPA has not commented in formal documents about when it considers pest adaptation to pest-protected plants to be an important public or social problem and when it considers resistance to be only a business problem or an insignificant public or social problem.

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