Submitted to: Environmental Biosafety Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/15/2003
Publication Date: 2/28/2004
Citation: Fuchs, M., Chirco, E.M., Gonsalves, D. 2004. Movement of coat protein genes from a commercial virus-resistant transgenic squash into a wild relative. Environmental Biosafety Research. 3(1):5-16. Interpretive Summary: Movement of pollen from transgenic commercial crops to wild relatives of that crop is a potential environmental concern for the deployment of transgenic crops. We studied the movement of pollen from commercial transgenic squash with resistance to zucchini yellow mosaic, watermelon mosaic 2, and cucumber mosaic viruses to susceptible wild squash that are found in the southern states of the U.S. Experiments were carried out in the field over a three-year period. Our results showed that the transgene for virus resistance moved to the wild squash under conditions where viruses were not severe in the wild squash, but not under conditions where the virus was severe. Seedlings resulting from seeds of wild squash that received pollen from the transgenic squash were resistant to the target viruses. Thus, our work show that the virus resistant trait from a commercial transgenic squash can occur under field conditions where the target viruses are not present or not severe. The presence of the virus in the wild squash population places severe limitations on the movement of transgene to wild squash. The reason is very likely because virus-infected wild squash are severely stunted and thus poor receptors of pollen, and fruit that do get pollinated have very few seeds and the germination rate of the seeds are low.
Technical Abstract: We monitored pollen-mediated transgene dissemination from commercial transgenic squash CZW-3 into its wild relative Cucurbita pepo ssp. ovifera var. texana (C. texana). Transgenic squash CZW-3 expresses the neomycin phosphotransferase II (NPT II) gene and the coat protein (CP) genes of Cucumber mosaic virus (CMV), Zucchini yellow mosaic virus (ZYMV), and Watermelon mosaic virus (WMV); thereby, it is resistant to these three aphid-borne viruses. The rate of NPT II and CP transgene introgression increased with overlapping flowering patterns and a high ratio of transgenic F1 hybrids (C. texana x CZW-3) to C. texana. Transgene transfer also readily occurred from transgenic F1 hybrids into C. texana over three generations in field settings where test plants grew sympatrically and viruses were not severely limiting the growth, and fruit and seed production of C. texana. In contrast, introgression of the transgenes into C. texana was not sustained under conditions of high viral disease pressure. As expected, C. texana progeny that acquired the CP transgenes exhibited resistance to CMV, ZYMV, and WMV. This is the first report on transgene dissemination from a transgenic crop that exhibits disease resistance and hybridizes with a wild plant species without loss of fertility.