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

Hybridization between crops and their weedy or wild relatives is an area of concern because the widespread use of genetically engineered crops may allow novel, bene®cial transgenes to enter nearby populations. We compared ®tness components of wild Cucurbita pepo from Arkansas, USA, with wild±crop hybrids derived from yellow squash (a cultivar of C. pepo with transgenic resistance to two viruses). Wild and hybrid progeny were grown in agricultural ®elds in Arkansas (1996±98) and Ohio (1996) in six similar experiments. Cross types (wild and hybrid) did not di€er signi®cantly in seedling survival, which exceeded 85% in all cases. In Ohio, where more detailed observations were made, hybrid plants produced 41% as many male ̄owers, 21% as many female ̄owers, and 28% as many seeds as wild plants. At all sites, ̄owering periods of the two cross types overlapped extensively. Putative virus symptoms were more common in wild plants than in hybrids. Lifetime fecundity varied considerably among sites and years. The average fecundity of hybrids ranged from 453 to 4497 seeds per plant and represented 15% ± 53% of the numbers of seeds produced by wild plants in the same experiments. These results suggest that the F1 generation does not represent a strong barrier to the introgression of neutral or bene®cial crop genes into free-living populations of C. pepo.