Transgenic Veggies Go Wild

A newly published study from Penn State details what can happen when a genetically modified organism escapes from captivity and interbreeds with the wild members of its species.

Transgenic organisms are critters that have been genetically engineered to express characteristics unique to their species. By snipping, swapping and splicing DNA between different species, organisms can be designed to provide specific benefits to people. For example, bacteria can be engineered to synthesis human insulin for treating diabetes, tomatoes can be manipulated to have an improved shelf-life, and pigs can be designed to more efficiently digest phosphorus, thus easing both their own cost of feeding and the amount of phosphorus pollution discharged into the surrounding environment. But, despite the potential benefits to people, what trouble could ensue if a transgenic organism were to evade human controls and escape its confinement? Would the transgenic organism out-compete the wild type and push it to extinction?

Cucurbita pepo is a species of squash cultivated around the world as a popular food; common varieties of the species include the zucchini, yellow squash and gourd. In addition to being commonplace at dinner tables, Cucurbita also maintains fame as a widely utilized transgenic plant – a transgenic plant that has managed to pass its transplanted genes to wild populations.

Prior to their escape, the genes of the Cucurbita plant had been engineered to have resistance to a leaf-wilting virus transmitted by aphids. The reasoning behind the genetic transplant was simple, by reducing susceptibility to the aphid borne disease, the agricultural yield of squash could be increased and more humans could be fed; but, having escaped, would the disease-resistant plants replace their naturally more disease-susceptible counterparts?

Not necessarily.

According to a case study just published in the November issue of the International Journal of Plant Sciences, when mixed populations of transgenic and wild type squash were naturally exposed to the aphid borne disease, the transgenic members did indeed exhibit better health – at least at first. After initially showing better health, the condition and reproductive success of the transgenic squash later equalized and balanced to that of the non-transgenic type. The reason for the equalization was that the robust appearance of the transgenic plants attracted the attention of leaf-munching, and bacteria-transporting, beetles. The beetles’ preference for the healthy looking plants affectively buffered any benefit the plants received from their introduced viral resistance.

Sasu, M., Ferrari, M., & Stephenson, A. (2010). Interrelationships among a Virus-Resistance Transgene. International Journal of Plant Sciences, 171 (9), 1048-1058 DOI: 10.1086/656531