Gene flow and rape - the Canadian experience

Herbicide tolerant cultivars developed by both induced mutation and gene tr ansfer occupied 50% of Canada's 5.2 million hectares of canola (Brassica na pus plus Brassica rapa) in 1998 and an expansion to 70 or 75% of the canola area is expected in 1999. Cultivars tolerant to S-triazine herbicides have been successfully grown in Canada since 1981. Early isolation studies in w estern Canada indicated an average outcrossing rate from large fields to sm all plots of 0.6 and 3.7% at 366 m for B. napus and B. rapa, respectively. However, 1998 data indicate a much lower outcrossing rate between large fie lds of herbicide tolerant and standard B. rapa and B. napus. Gene flow betw een herbicide tolerant B. napus cultivars and stacking of resistance genes in volunteer B. napus plants was observed in a commercial field when a prod ucer did not follow agronomic and herbicide recommendations. The weeds Raph anus raphanistrum, Hirschfeldia incana and Brassica nigra are absent or unc ommon in western Canada. However, the weed dog mustard (Erucastrum gallicum ) is abundant and inter-generic hybrids, using E. gallicum as the male, hav e been obtained in crosses with B. napus and B. rapa. Selfed and backcross progeny are under investigation.