Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/1998
Publication Date: N/A
Interpretive Summary: The wild relatives of cultivated sunflower co-existed for many years in nature where there has been a continuous exchange of genes between the wild and cultivated sunflower. Genes from the wild species have conferred resistance to some of the major diseases in cultivated sunflower. With the advent of biotechnology, new genetic combinations are available with altered genetic structure in sunflower. The question being asked is how will the new genetic combinations influence the native species and will they become more competitive and become problem weeds. In order to assess the ease with which crop-to-wild introgression can proceed, we compared characteristics of F1 wild-crop progeny with those of purely wild species. The crop hybrid was nontransgenic. The wild-crop hybrids generally had higher germination (less dormancy) than the wild progenitors. Flowering periods of hybrids and wild progeny overlapped considerably suggesting that hybrids were likely to backcross with the wild parents. In general, hybrid plants had fewer branches, flower heads and seed than the wild plants. Wild-crop hybrids appeared to have lower fitness than the wild species, but the F1 barrier to introgression of crop genes is quite permeable. Specific transgenic sunflower genes will have to be carefully monitored when introduced into the agro-ecosystem.
Technical Abstract: Wild-crop hybridization has the potential to introduce beneficial traits into wild populations. Gene flow from genetically engineered crops, in particular, can transfer genes coding for traits such as resistance to herbicides, insect herbivores, disease, and environmental stress into wild plants. Cultivated sunflower (Helianthus annuus) hybridizes spontaneously with wild/weedy populations (also H. annuus), but little is known about the relative fitness of F1 hybrids. In order to assess the ease with which crop-to-wild introgession can proceed, we compared characteristics of F1 wild-crop progeny with those of purely wild genotypes. Two nontran- sgenic, cultivated varieties were crossed with wild plants from three different regions (Texas, Kansas, and North Dakota). Seed burial experi- ments in the region of origin showed that wild-crop seeds had somewhat higher germination rates (less dormancy) than wild seeds from Kansas and North Dakota, while no differences were seen 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 lifetime fecundity and flowering phenology. Flowering periods of hybrid and wild progeny overlapped considerably, especially in plants form North Dakota and Texas, suggesting that these hybrids are very likely to backcross with wild plants. In general, hybrid plants had fewer branches, flower heads, and seeds than wild plants, but in two crosses the fecundity of hybrids was not significantly different from that of purely wild plants. In summary, our results suggest that F1 wild-crop hybrids had lower fitness than wild genotypes, especially when grown under favorable conditions, but the F1 barrier to the introgession of crop genes is quite permeable.