CROP-TO-WEED GENE FLOW IN THE GENUS SORGHUM (POACEAE) - SPONTANEOUS INTERSPECIFIC HYBRIDIZATION BETWEEN JOHNSONGRASS, SORGHUM-HALEPENSE, AND CROP SORGHUM, SORGHUM-BICOLOR

The role of crop-to-weed gene flow is often controversial and overlook ed. As a consequence, the likelihood of spontaneous crop-to-weed hybri dization in most crop/weed systems is generally unknown. The lack of d ata relating to the formation of crop/weed hybrids has particular cont emporary significance when considering the wide scale commercial relea se of transgenic crop plants and the potential for escape of engineere d genes via crop-to-weed hybridization. We created an experimental sys tem whereby we could examine the incidence and rate of spontaneous cro p-to-weed hybridization between Sorghum bicolor and S, halepense, john songrass. An isozyme marker was used to identify hybrid plants through progeny testing. Incidence and rate of hybridization were highly vari able with respect to weed distance from the crop, location of the stud y site, and year the study was performed. Crop/weed hybrids were detec ted at distances of 0.5-100 m from the crop. Interspecific hybridizati on can and does occur in this system at a substantial and measurable r ate. Transgenes introduced into crop sorghum can be expected to have t he opportunity to escape cultivation through interspecific hybridizati on with johnsongrass. Traits that prove to be beneficial to weeds poss essing them can be expected to persist and spread. This is an issue th at needs to be addressed when developing biosafety guidelines for the commercial release of transgenic sorghums.