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One of the most striking features of the Brassica genus is the wide range of morphological diversity within cultivated species. Different morphs have been selected for a variety of uses, including as vegetables, oilseeds, forages, and condiments. This variation is most apparent within B. rapa (syn. campestris; n = 10) and B. oleracea (n = 9), where broad, parallel diversity exists for many vegetable forms (Fig. 1). Brassica napus (n = 19), the amphidiploid species derived from hybridization of B. rapa and B. oleracea (U 1935) also includes diverse crop forms, such as winter and spring oilseed rape, rutabagas, and fodder rape. Many different components of plant growth and development contribute to this morphological variation, and each of these components may be under complex genetic control. Thus, it has been difficult to obtain a comprehensive picture of the genetic control of morphological diversity in Brassica crops. However, a major component of this diversity is variation in flowering time, and for this trait considerable progress in our understanding has been made. |
