**7. Oilseed rape breeding**

Breeding is an excellent tool for improving many crops' preferred characteristics. The most common desirable traits usually are higher yield, resistance to stress and diseases, and improvement of specific characteristics of the plant. Breeding is a time and resource-consuming technique. The process of cultivar development, starting with initial crosses and finishing with commercial registration, takes about 10 years. Many advances have been achieved in oilseed rape improvement due to the collaborative effort of plant breeders, pathologists, physiologists, agronomists, and other specialists. These efforts reduced production risks for farmers who grow these cultivars and resulted in greater seed yield, modified content of seeds, earlier maturity, disease, and pod shatter tolerance [1, 4].

Crosses are made between perspective genetic material and selected for desirable seed yield, the presence and content of seed components, e.g., specific amino and fatty acids, oil, protein etc. During the oilseed rape breeding history, the contents of unwanted compounds found in the oil, such as erucic acid and glucosinolates, were significantly decreased to ensure safe use for edible purposes. Moreover, the oil content, seed yield, and disease resistance have also significantly improved. Knowledge about the relationships between closely related species is essential for plant breeders. It is an excellent source of genetic material for developing new cultivars. There is a significant number of created winter and spring oilseed rape cultivars. They are sorted according to their characteristics [1, 12, 23].

HO and LL (high oleic and low linolenic fatty acid content) cultivars, due to the modified contents of oleic and linolenic fatty acids, are healthier for human health. The stable oil of HO and LL varieties benefits the food processing industry [7, 15, 43].

LEAR (low erucic acid oilseed rape) development started in 1960, when oilseed rape plants with low eicosenoic and erucic acid contents were isolated by Canadian breeders after the high eicosenoic and erucic fatty acid contents were questioned. Soon, in 1967, seeds of cultivar 'Bronowski' were found to have a low content of glucosinolates. This genetic source of low concentration of glucosinolates was then used to develop cultivars with low levels of erucic acid and glucosinolates ("double low" cultivars). Multiple improvements of oilseed rape cultivars throughout the breeding process dramatically reduced erucic acid levels. These cultivars are used for edible oil production. The current standard requirement for these cultivars is less than 2% of erucic acid in the fatty acid profile and less than 30 micromoles of any one or a mixture of the glucosinolates (3-butenyl glucosinolate, 4-pentenyl glucosinolate,

#### *Oilseed Rape: Biology, Use, Current Cultivation Issues and Agronomic Management DOI: http://dx.doi.org/10.5772/intechopen.109180*

2-hydroxy-3 butenyl glucosinolate, and 2-hydroxy- 4-pentenyl glucosinolate) per gram of air dry and oil-free solid. The reduction of the content of glucosinolates expanded the use of oilseed rape meals in animal husbandry [1, 3, 7, 16].

HEAR cultivars were developed for non-edible purposes. They are commonly grown for industrial use. HEAR cultivars are used to produce lubricants, plastics, lacquers, and detergents. Reducing the levels of glucosinolates enabled the usage of HEAR cultivars as livestock feed [5, 23].

The characteristics of oilseed rape can also be modified by hybrid seed production. An oilseed rape hybrid results from crossbreeding two oilseed rape lines. And the more distant the parents, the greater the hybrid power. It was observed that hand crosses between two distant lines of oilseed rape result in up to 45 per cent higher seed yield than in parent lines. It was shown that oilseed rape hybrids have higher stability, disease resistance, and yield. However, the by-hand method is time and sourceconsuming and thus hardly possible at a large scale. Since oilseed rape cultivars are mostly self-pollinated thus, self-pollination of parental lines must be controlled during the hybrid creation process. Therefore, several approaches have been developed to produce oilseed rape hybrids [7, 12].

One of the developed hybridisation systems is the cytoplasmic male sterility (CMS) system. The first commercial CMS oilseed rape hybrid was registered in 1989. Its use enables oilseed rape breeders to produce female plants that either do not produce pollen, do not shed pollen or make pollen that cannot cause self-fertilisation. Its use allows canola breeders to grow female plants that either fail to produce pollen, do not shed pollen, or which pollen cannot self-fertilise. This system was invented after discovering that some *Brassica* species have male-sterile cytoplasm. Fertility is determined by an interaction of the nucleus and cytoplasm. A mutation in certain cytoplasmic bodies disables the development of functional pollens or anthers [3–5].

The hybrid system usually consists of three lines: a male sterile, a maintainer and a restorer line. The male sterile female plant flowers have a sterile cytoplasm due to the gene isolated from the soil bacterium and inserted into this line. The inserted gene controls the production of the particular enzyme in the specific cell layer. It disables the development of pollen. Thus, these plants cannot self-pollinate. These flowers are crossed with the genetically identical maintainer line, which produces pollen. This line contains another gene obtained from the same soil bacterium. This gene has an inhibitor enzyme that counteracts the sterility enzyme in the male sterile line to restore fertility. The obtained seeds maintain CMS characteristics. The restorer line is genetically different from the male sterile line. It contains genes that compensate for the cytoplasm gap and restores fertility in the hybrid. The 100 per cent hybrids are obtained by inserting the target gene into both parental lines. A hybrid tolerant to the herbicide glufosinate ammonium was developed using this kind of breeding technique [5, 44].

The other breeding method is the production of "synthetic" cultivars. It exploits the heterosis present in the Brassica family. Synthetic oilseed rape cultivars are developed by mixing seeds from two or more parental lines from two lines and by growing out the mixed seed to produce certified synthetic seed. The synthetic seed, including hybrid and parental plants, is more stable under various environmental conditions than conventional cultivars. The degree of outcrossing depends on the insect pollination degree; thus, it is unpredictable. A mixture of the parental lines and all possible hybrids between them will be obtained in the next generation. A list of herbicidetolerant cultivars has been developed using mutagenesis and gene transfer. These cultivars are tolerant to specific herbicides or their groups. The first triazine-tolerant

oilseed rape was registered in 1984 in Canada. It was developed to enable the cultivation of oilseed rape in areas infested with weeds of the *Brassicaceae* family, e.g., wild mustard, stinkweed, and ball mustard. Later, cultivars tolerant to imidazolinone, glyphosate (Roundup), glufosinate ammonium and bromoxynil were developed. It was demonstrated that isogenic lines have different energy use efficiencies under certain growing conditions due to epigenetic differences [1, 5, 45].
