FECUNDITY, PHENOLOGY, AND SEED DORMANCY OF F-1 WILD-CROP HYBRIDS IN SUNFLOWER (HELIANTHUS-ANNUUS, ASTERACEAE)

Crop-to-wild hybridization has the potential to introduce beneficial t raits into wild populations. Gene flow from genetically engineered cro ps, in particular, can transfer genes coding for traits such as resist ance to herbicides, insect herbivores, disease, and environmental stre ss into wild plants. Cultivated sunflower (Helianthus annuus) hybridiz es spontaneously with wild/weedy populations (also H. annuus), but lit tle is known about the relative fitness of F-1 hybrids. In order to as sess the ease with which crop-to-wild introgression can proceed, we co mpared characteristics of F-1 wild-crop progeny with those of purely w ild genotypes. Two nontransgenic, cultivated varieties were crossed wi th wild plants from three different regions-Texas, Kansas, and North D akota. Seed burial experiments in the region of origin showed that wil d-crop seeds had somewhat higher germination rates (less dormancy) tha n wild seeds from Kansas and North Dakota, while no differences were s een in seeds from Texas. Progeny from each type of cross were grown in outdoor pots in Ohio and in a weedy field in Kansas to quantify lifet ime fecundity and flowering phenology. Flowering periods of hybrid and wild progeny overlapped considerably, especially in plants from North Dakota and Texas, suggesting that these hybrids are very likely to ba ckcross with wild plants. In general, hybrid plants had fewer branches , flower heads, and seeds than wild plants, but in two crosses the fec undity of hybrids was not significantly different from that of purely wild plants. In Ohio, wild-crop hybrids from North Dakota appeared to be resistant to a rust that infected 53 % of the purely wild progeny, indicating a possible benefit of ''traditional'' crop genes. In summar y, our results suggest that F-1 wild-crop hybrids had lower fitness th an wild genotypes, especially when grown under favorable conditions, b ut the F-1 barrier to the introgression of crop genes is quite permeab le.