Fecundity of transgenic wild-crop hybrids of Cucurbita pepo (Cucurbitaceae): implications for crop-to-wild gene flow

Hybridization between crops and their weedy or wild relatives is an area of concern because the widespread use of genetically engineered crops may all ow novel, beneficial transgenes to enter nearby populations. We compared fi tness components of wild Cucurbita pepo from Arkansas, USA, with wild-crop hybrids derived from yellow squash (a cultivar of C. pepo with transgenic r esistance to two viruses). Wild and hybrid progeny were grown in agricultur al fields in Arkansas (1996-98) and Ohio (1996) in six similar experiments. Cross types (wild and hybrid) did not differ significantly in seedling sur vival, which exceeded 85% in all cases. In Ohio, where more detailed observ ations were made, hybrid plants produced 41% as many mate flowers, 21% as m any female flowers, and 28% as many seeds as wild plants. At all sites, flo wering periods of the two cross types overlapped extensively. Putative viru s symptoms were more common in wild plants than in hybrids. Lifetime fecund ity varied considerably among sites and years. The average fecundity of hyb rids ranged from 453 to 4497 seeds per plant and represented 15% - 53% of t he numbers of seeds produced by wild plants in the same experiments. These results suggest that the F-1 generation does not represent a strong barrier to the introgression of neutral or beneficial crop genes into free-living populations of C. pepo.