Experimental assessment of gene flow between transgenic squash and a wild relative in the center of origin of cucurbits

The introgression of modified genetic sequences (transgenes) into wild populations hinges on the generation of viable and fertile hybrids from crosses between transgenic cultivars and their wild relatives. We assessed the risk of escape of a gene construct that confers resistance to three viruses (ZYMV, WMV, CMV) from a transgenic zucchini (Cucurbita pepo) to Cucurbita argyrosperma ssp. sororia, a wild relative at the center of origin of the genus in Mexico. We experimentally generated first and second generation hybrids, as well as backcross progeny (BC), and evaluated their performance. The virus-resistance transgene was successfully inherited into both hybrid generations and also to BC progeny from the crosses of hybrids with the wild relative. The transgene generally followed Mendelian inheritance as a dominant trait. Both hybrid generations and the BC progeny had lower reproductive output compared to the wild parent. Given that the hybrid and BC progeny were viable and fertile, the escape and persistence of the transgene is possible via wild populations of C. argyrosperma ssp. sororia. This information is essential for biosafety policy in Mexico-center of origin and diversification of several crops-where the liberation of genetically modified plants is currently under approval, and risk assessment is necessary.