ABSTRACT
Brassicas have great economic value and encompass a great diversity of plants. They are grown as vegetables, fodder, sources of oils and condiments. The morphological variation present within Brassica species is enormous and from several species practically every part of the plant is used by man. This includes the leaves in crops like heading cabbages and the leafy types that do not form heads (pak choi, komatsuna, etc.), the terminal and axillary buds in caulifl ower, broccoli, broccoletto, the seedpods in seed stalk mustard, the swollen stems in taitsai and kohlrabi, the swollen roots in turnips and swede and the seeds in all oil crops. In this chapter, the focus will be on three important Brassica vegetable crops that belong to Brassica rapa, Brassica oleracea and Brassica juncea, and on Raphanus sativus, the radishes. Since B. rapa, B. juncea and R. sativus also include morphotypes that are cultivated as oil crop and/or condiments, the diversity analyses also extends to the oil crops. For both B. rapa and B. juncea the diversity within and between morphotypes and the taxonomic relationships between the vegetable and oil types are discussed. Besides the genetic diversity in R. sativus, the phylogenetic relationships between radish and B. rapa/B. oleracea and B. nigra are also discussed. Table 3-1 gives an overview of the different subspecies within the three Brassica species and R. sativus classifi ed according to the organs that are used for consumption and Fig. 3-1 depicts the different crop types within B. rapa. In the different paragraphs for each species the origin of the species is discussed, the crop types are introduced and an overview of studies on the genetic diversity within that species is presented. In the subchapters on B. oleracea, B. rapa and R. sativus diversity of wild related species that have played a role in the evolution of the different crop types is also discussed. Before we describe the different Brassica and Raphanus species, an overview is given of the taxonomic position of these genera/species in the Brassicaceae family.
