Nuclear genetic control of variation in simazine tolerance in oilseed brassicas. I. Brassica napus

Substantial variation in tolerance to the triazine herbicide simazine was observed among a wide range of Brassica napus cultivars grown in a hydroponic screening system. None of these cultivars was as tolerant of the simazine treatment as the Canadian cultivar Triton which carries cytoplasmic gene(s) which confer a high level of resistance through their modification of chloroplast membranes to which triazine herbicides normally bind. A field study showed that the most tolerant cultivar Haya had a significantly higher yield than Triton in both handweeded plots and plots treated with 1000 ml/ha simazine. This finding supported other observations that the yield potential of cultivars such as Triton is substantially reduced because of the impairment of photosynthesis by cytoplasmic gene(s) for triazine resistance.