DEVELOPMENT AND VALIDATION OF A MODEL FOR THE SPREAD AND MANAGEMENT OF AN ESCAPED VIRUS RESISTANT TRANSGENE IN WILD POPULATIONS OF CUCURBITA

The recent commercialization of numerous transgenic versions of crop species has provided many opportunities for U.S. agriculture that benefit both the grower and consumer. Herbicide-tolerant and insect- and virus-resistant crops provide farmers with a wide range of managerial and financial opportunities. While the benefits to agriculture of transgenic crops are clear (e.g., reduced need for pesticides, greater profit margins, and reduced pest loads on other crop species), continued assessment of the potential ecological risks posed by the introduction of transgenes and strategies for the mitigation of these risks are needed to assure that genetic technologies provide safe and sustainable benefits for the U.S. consumer and protection of our natural habitats and biodiversity. Gene flow from cultivated to free-living taxa of Cucurbita (squash) is common and well-documented. In 1996, a transgenic cultivar was deregulated with resistance to three viral diseases. By 1999, several cultivars with the transgene were developed, marketed, and grown commercially throughout the US where it greatly reduced pesticide use and increased yield. It is likely that the transgene has been introduced to natural populations repeatedly. Non-transgenic free-living Cucurbita have long been recognized as an important weed in soybean and cotton fields in some locations. Further, free-living squash can serve as sources of herbivores and pathogens even when they are not in direct competition with crops. Whether introgression of the transgene into wild populations of Cucurbita will result in a more problematic weed for farmers or if it poses a threat to natural biodiversity depends upon the fitness of the introgressives bearing the transgene. We intend to develop a fully stochastic, individual based simulation model to predict changes in the frequency of the transgene from one generation to the next across a range of conditions. We then design key experiments to parameterize and refine the model. Specifically, we will perform a series of large scale, replicated, field experiments with the entire Cucurbita pathosystem that are designed to quantify the costs associated with the cultivar traits during introgression; quantify the direct costs of the transgene in the absence of the virus; estimate the indirect ecological costs of the transgene across a range of relevant environmental conditions; and quantify the transmission rate for both the virus and the bacterial pathogens across a range of environmental conditions. These studies will result in a fully parameterized and validated model that predicts the fate of an escaped transgene into free-living populations of Cucurbita. We will explore via simulations: A) the breadth of conditions that would favor the increase of the transgene in wild populations (useful for both monitoring and management); B) the rate of transgene introgression under repeated escape from cultivated varieties, and C) various management options for controlling transgenic plants should they become problematic.