ABSTRACT
B. napus ssp. napus is cultivated as a winter or summer annual crop in temperate climates of northern Europe, Canada, the USA, New Zealand, China, Japan and Australia (Cowling 2007). Winter rapeseed can only turn from vegetative to generative growth after a long period of vernalization; semi/winter rapeseed from China only needs a short vernalization period and spring rapeseed from Canada, Australia and northern Europe reproduces without vernalization. Additionally Chinese rapeseed types are less sensitive to daylength (Momoh et al. 2002). The oil is either used as vegetable oil for consumption or as raw material for a wide array of industrial products. Industrial rapeseed is high in erucic acid and glucosinolates and is used for non-edible purposes. In 1968 the fi rst low erucic acid cultivar was produced in Canada (Daun 1983), and in 1974 the fi rst double low or double zero cultivar was introduced, which was low in both erucic acid (less than 2%) and glucosinolates (less then 30 µmol/g) (Steffanson 1983). These cultivars, bred in Canada, were called canola cultivars and replaced almost all high glucosinolate cultivars; this domestication bottleneck restricted the genepool in canola breeding programs considerably (Cowling 2007).
