Low intraspecific competitive fitness in a triazine-resistant,nearly nuclear-isogenic line of Brassica napus

The maternally-inherited triazine-resistant biotypes that have appeared usually have had a much reduced competitive fitness. As such studies did not use nuclear isogenic material, we tested rapeseed cv. Regent that had had triazine resistance introduced from Brassica campestris and was then extensively backcrossed to cv. Regent. Seeds of each biotype were alternated at 5-cm spacing to ascertain competitive fitness and various growth parameters were followed. The fresh weight, dry weight, number and weights of siliques (seed pods) and yield of seed of the interplanted triazine-resistant biotype were all less than one-third of the susceptible biotype.