Academic and Economic Importance of Brassica napus Rapeseed
Rapeseed or canola (B. napus) is the second most important oilseed crop of the world. It is also a favourite plant for basic and breeding research. Due to its origin and evolution, rapeseed has a complex polyploid genome. Recent sequencing of the corresponding genomes provides the basis for a better understanding and exploitation of the genetic diversity involved in major rapeseed traits. However, directed selection for major quality characteristics, i.e. minimal erucic acid content and low glucosinolate level, has caused genetic bottlenecks limiting genetic variation in the current gene pools of cultivated oilseed rape (OSR) Therefore, broadening genetic diversity is an important aim of research and a necessary prerequisite for further progress by OSR breeding. In agricultural production, rapeseed is nowadays an indispensable component of crop rotations in major growing areas such as Australia, Western Canada, Central China and many countries of the European Union. In many cases, OSR is the only leaf crop among dominating cereal species. Therefore, OSR as a component of crop rotations helps to maintain soil fertility and contributes to sustainable production therefore. As a major cash crop OSR substantially contributes to farmers' incomes and therefore helps to stabilize rural populations. Beyond that, as major globally traded agricultural commodities rapeseed/canola and rapeseed/canola oil and meal significantly input the national products of a number of countries e.g. Canada. Rapeseed/canola is a raw material for vegetable oil and extraction meal as feed, food and fuel. The oil is mainly used as a high value salad oil for dressings etc. due to its high contents of oleic acid (ca. 60% and poly unsaturated linolenic acid (omega 3, ca. 10% Nevertheless, a large part is also used as a mobility fuel for diesel cars and tractors, particularly in Germany and Europe. The extraction meal (and protein) from oil processing is now recognized as a highly valuable animal feed, particularly for ruminants (cattle) but also for monogastric farm animals (pigs, poultry) Furthermore, the interest in rapeseed protein for the purpose of human nutrition is increasing. Optimal contents of the major compounds mentioned before represent the main requirements for rapeseed/canola varieties today. Consequently, quality characteristics are major criteria for variety testing and registration therefore. Other major requirements for modern rapeseed varieties are yield and various agronomic traits securing seed yield, i.e. resistance against fungal diseases and insect pests. Because of the environmental concerns and the rejection of agrochemicals such as insecticides (e.g. ban of neonicotinoids in the EU) genetic approaches of establishing resistant crop cultivars constantly gain importance. OSR breeding has long been a relatively ordinary process of repeated selection for resistance, quality and yield, the propagation of improved populations and their release as new open pollinated (OP) varieties. Since this approach is not very effective, breeders have been interested in breeding hybrids instead. Today, F1 hybrids represent the major variety type. They are produced with genetic male sterility systems, most of which are based on cytoplasmic mutations causing male sterility (cms) The higher performance of hybrids is caused by "heterotic effect" which largely depends on the genetic distance between the parents. Therefore, distant genetic pools need to be generated for the development of female and male parents. The future potential of variety design is consequently determined by the usefulness of the genetic pools and the performance of hybrid parents extracted from them. Modern breeding tools based on biotechnology and genomics can substantially contribute to a better exploitation of useful genetic diversity, i.e. specific genes and genetic networks. Better varieties are a precondition for further crop improvement. Future quality OSR cultivars deserve high yield potential, combined with good stability due to disease and pest resistance. This will be the basis for exploiting the great agronomical and industrial advantages of the rapeseed plant.