“Canola”, refers to a particular class of rapeseed (Brassica napus oleifera annua) having: (i) a seed oil that contains less than 2% erucic acid, and (ii) an oil-free meal that contains less than 30 micromoles aliphatic glucosinolates per gram of meal. Canola seed is pressed for cooking oil and the residual meal is used as an organic fertilizer and as a high-protein animal feed supplement. Industrial uses of canola include biodiesel and plastic feedstocks.
Farmers in Canada began producing canola oil in 1968. Early canola cultivars were known as single zero cultivars because their oil contained 5% or less erucic acid, but glucosinolates were high. In 1974, the first licensed double zero cultivars (low erucic acid and low glucosinolates) were grown. Today all canola cultivars are double zero cultivars. The Canadian Health and Welfare Department recommended conversion to the production of low erucic acid varieties of rapeseed. Industry responded with a voluntary agreement to limit erucic acid content to less than 5% in food products, effective Dec. 1, 1973. In 1985, the U.S. Food and Drug Administration granted canola oil GRAS (Generally Recognized as Safe) status for use in human foods.
Because canola oil is perceived to be “healthy”, its use is rising steadily both as an oil for cooking and as an ingredient in processed foods. The consumption of canola oil is expected to surpass corn and cottonseed oils, becoming second only to soybean oil. It is low in saturated fatty acids and high in monounsaturated fatty acids, containing a high level of oleic acid. Many people prefer the light color and mild taste of canola oil over olive oil, the other readily available oil high in monounsaturates.
Canola is an important and valuable field crop. The goal of a canola breeder is to develop new, unique, and superior canola cultivars and hybrids having improved combinations of desirable traits and therefore, increased economic value. Improved performance is manifested in many ways. Higher yields of canola plants contribute to higher seed production per acre, a more profitable agriculture and a lower cost of products for the consumer. Improved plant health increases the yield and quality of the plant and reduces the need for application of protective chemicals. Adapting canola plants to a wider range of production areas achieves improved yield and vegetative growth. Improved plant uniformity enhances the farmer's ability to mechanically harvest canola. Improved nutritional quality increases its value in food and feed.
Canola is a dicot plant with perfect flowers, i.e., canola has male, pollen-producing organs and separate female, pollen receiving organs on the same flower. Canola flowers are radial with four sepals alternating with four petals forming the typical cross pattern from which the Cruciferae family derives its name. In addition, canola flowers consist of two short lateral stamens, four longer median stamens and a stigma. Pollination occurs with the opening of the anthers and shedding of pollen on the stigma or with the deposit of pollen on the stigma by insects. Canola flowers are mainly self-pollinating, although outcrossing occurs when pollen is transferred from the anthers to the stigmas by wind or bees or other insects. After fertilization, which is usually complete within 24 hours of pollination, the syncarpous ovary elongates to form a silique (pod). Because each pod may contain 25 or more seeds and each plant produces many pods, the multiplication rate per generation usually exceeds 1,000 to 1, thereby accelerating the breeding and evaluation process.
The development of new cultivars in a canola plant breeding program involves numerous steps, including: (1) selection of parent canola plants (germplasm) for the initial breeding crosses; (2) producing and selecting inbred breeding lines and cultivars by either the doubled-haploid method or repeated generations of selfing individual plants, which eventually breed true; (3) producing and selecting hybrid cultivars by crossing a selected inbred male-sterile line with an unrelated inbred restorer line to produce the F1 hybrid progeny having restored vigor; and (4) thoroughly testing these advanced inbreds and hybrids compared to appropriate standards for three or more years in environments representative of the commercial target area(s). The best inbred and hybrid experimental cultivars then become candidates for new commercial cultivars. Those lines still deficient in a few traits may be used as parental lines to produce new populations for further selection.
Development and selection of new canola parental lines, the crossing of these parental lines, and selection of superior hybrid progeny are vital to maintaining a canola breeding program. The F1-hybrid canola seed is produced by manual crosses between selected male-fertile parents or by using male-sterility systems. These hybrids are selected for certain single-gene traits such as pod color, flower color, pubescence color or herbicide resistance, which can indicate that the seed is truly a hybrid from the intended cross. Additional data on parental lines, as well as the phenotype of the hybrid, influence the breeder's decision whether to continue with the specific hybrid cross.
The method of doubled-haploid breeding consists of donor selection, microspore culture and chromosome doubling, embryo cold stress, plantlet regeneration, ploidy analysis, and self-pollination to produce seed of doubled-haploid lines. The advantage of the doubled-haploid method is that the time to develop a new completely homozygous and homogeneous cultivar can be reduced by 3 years compared to the conventional inbreeding method of multiple generations of self pollination.
When two different, unrelated canola parent cultivars are crossed to produce an F1 hybrid, one parent cultivar is designated as the male, or pollen parent, and the other parent cultivar is designated as the female, or seed parent. Because canola plants are capable of self-pollination, hybrid seed production requires elimination of or inactivation of pollen produced by the female parent. Different options exist for controlling male fertility in canola plants such as physical emasculation, application of gametocides, and cytoplasmic male sterility (CMS).
Hybrid canola seed can be produced on a commercial scale by means of a system whereby the female parent has an allele in the mitochondrial genome for cytoplasmic male sterility and the male parent has an allele in the nuclear genome for fertility restoration (Rf). Cytoplasmic male sterility prevents the production of functional pollen, thereby preventing self pollination of the female parent. Pollen from the male parent planted in close proximity to the female parent is then able to freely cross pollinate the female parent to produce hybrid seed. The fertility-restoration allele contributed by the male parent to the seed embryo enables the hybrid crop plants to be male fertile. The resulting hybrid canola crop, which is fully fertile, may then demonstrate heterosis (increased vigor) to produce grain yields potentially greater than that of inbred cultivars.
A cytoplasmic male-sterile inbred (A) line is genetically maintained and increased in a breeding and hybrid-production program by growing it in isolation with a male-fertile maintainer (B) line that is normal (N) for cytoplasmic fertility and is homozygous recessive at the nuclear male-fertility restoration locus (rfrf). All seed harvested from the A line is then male sterile (S rfrf) and all seed harvested off the B line is male fertile (N rfrf). The A line is then maintained, increased, and used as the female parent for hybrid seed production in combination with an unrelated male parent that has the dominant allele (Rf) for male fertility restoration.
One example of a CMS system in canola hybrid production and breeding is the Ogura (Ogu) cytoplasm and its specific nuclear fertility-restoration gene, Rfo—a system discovered in radish (Raphanus sativus) and transferred to Brassica napus after protoplast fusion. The system was later improved by breeding to lower the glucosinolate content for hybrid canola.
These processes, which lead to the final step of marketing and distribution of a cultivar, usually take from 8 to 12 years from the time the parental cross is made. Therefore, development of new canola inbred and hybrid cultivars is a slow, costly process that requires the resources and expertise of plant breeders and numerous other specialists.
It is nearly impossible for two canola breeders to independently develop genetically-identical canola inbreds or hybrids expressing all the same trait characteristics. The cultivars that are developed cannot be predicted because the breeder's selection occurs in unique environments, with no control over meiotic genetic recombination (using conventional breeding procedures), and with millions of different possible genetic combinations possible. A breeder of ordinary skill in the art cannot predict the final resulting lines he/she develops, except possibly in a very gross and general fashion. The same breeder cannot produce the same cultivar twice by using the exact same original parents and the same selection techniques.
Canola cultivars and other sources of canola germplasm are the foundation material for all canola breeding programs. Despite the existence and availability of numerous canola cultivars and other source germplasm, a need still exists for the development of improved germplasm to improve and maximize yield and quality.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification.
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