Risks of gene flow from transgenic herbicide-resistant canola (Brassica napus) to weedy relatives in southern Australian cropping systems

It is likely that transgenic canola expressing genes encoding resistance to glyphosate and glufosinate ammonium will be introduced into the Australian cropping system in the next few years. One risk associated with the introd uction of such cultivars is the release of herbicide resistance genes into weedy relatives of canola. This review examines the currently available exp erimental information regarding the possibility of gene flow from canola to weedy relatives. Three species are identified as having the potential to o utcross with canola, Brassica juncea, B. rapa, and Raphanus raphanistrum. T wo of these species are not yet widespread weeds of the southern Australian cropping zone. In contrast, R. raphanistrum is already a major weed in Aus tralia with existing resistance to ALS-inhibiting herbicides. Information i s urgently needed to determine whether successful hybrids between B. napus and R. raphanistrum can be produced under Australian conditions. Major defi ciencies in the existing information are identified in relation to some oth er important weed species within the southern Australian cropping zone. Fur ther studies are required to determine the out-crossing potential of canola to B. tournefortii, Diplotaxis tenuifolia, Sisymbrium officinale, and S. o rientale if transgenic canola is to be safely and responsibly introduced in to Australia.