Brassica (PROSEA Oils and fats)
Brassica L. (oilseed crops)
- Protologue: Sp. pl. 2: 666 (1753); Gen. pl., ed. 5: 299 (1754).
- Family: Cruciferae
- Chromosome number: x= 8 (B genome), 9 (C genome), 10 (A genome); B. juncea: 2n= 36 (AABB); B. napus: 2n= 38 (AACC); B. rapa: 2n= 20 (AA)
Major taxa and synonyms
- Brassica juncea (L.) Czern. cv. group Oilseed Mustard (cv. group name proposed in Prosea 8: 105 (1993)); other classifications of cultivars of B. juncea (L.) Czern. that are grown for their oilseeds: var. juncea, Juncea Group, Mustard Group, Raya Group.
- Brassica napus L. cv. group Colza (cv. group name proposed in Prosea 8: 284 (1993)); other classifications of cultivars of B. napus that are grown for their oilseeds: subsp. napus, subsp. oleifera auct., Napus Group, Oil Rape Group.
- Brassica rapa L. cv. group Oilseed Turnip (cv. group name proposed here); other classifications of cultivars of B. rapa that are grown for their oilseeds: Winter Turnip Rape Group (Oleifera Group, Navette d'hiver Group), Spring Turnip Rape Group (Praecox Group, Navette d'été Group), Tori Group (Dichotoma Group), Brown Sarson Group, Yellow Sarson Group (Trilocularis Group).
- rapeseed, brassica oilseed.
B. juncea cv. group Oilseed Mustard:
- Indian mustard, brown mustard, sarepta mustard (En)
- Moutarde indienne, moutarde brune (Fr)
- Indonesia: sawi, sesawi
- Malaysia: sawi, pahit, kai choy
- Philippines: mustasa (Tagalog)
- Cambodia: khat naa
- Laos: kaad khièw
- Thailand: phakkat-khieo, phakkat-khiepli (central)
- Vietnam: cải canh, cải bẹ xanh.
B. napus cv. group Colza:
- rapeseed, oilseed rape (En)
- Colza oléagineux (Fr).
B. rapa cv. group Oilseed Turnip:
- rapeseed, turnip rape, toria, sarson (brown or yellow) (En)
- Navette (Fr).
The name summer or spring rapeseed refers to annual types of B. rapa and B. napus sown in spring; the name winter rapeseed to biennial types sown in autumn. The corresponding names in French are: navette de printemps and navette d’hiver for B. rapa and colza de printemps and colza d’hiver for B. napus.
Origin and geographic distribution
The primary centre of origin of B. juncea is believed to be the foothills of the Himalayas in central Asia. From here, three secondary centres developed: one in India and one in the Caucasus for the oilseed forms and one in China for the leafy forms. The occurrence of both parent species in the Middle East, however, poses strong evidence to also consider that region as a primary centre. Primary centres of origin for B. napus are western Europe, for B. rapa the Mediterranean and Afghan-Pakistan regions. Domestication of B. rapa and B. juncea as oilseed crops of the cool season probably started more than 4000 years ago in South and East Asia. Rapeseed and to a lesser extent Indian mustard have retained a prominent position as sources of edible oil in India, Pakistan, Bangladesh and China and continue to do so today. By the 14th Century, B. rapa had become a major crop in the Netherlands and subsequently in other countries of north-western Europe in response to ever increasing demands for lamp oil. Some 300 years later, a new type of rapeseed (B. napus) was also developed in the Netherlands, more resembling a kale plant, without the turnip-like root and producing an oil equally suitable for lighting and industrial lubrication. Rapeseed cultivation in Europe started to decline towards the end of the 19th Century with the advent of electricity and petroleum products. Traditional rapeseed oil never attained general popularity as an edible oil in Europe because of its peculiar pungency. In the 1960s, higher yielding cultivars of both B. rapa and B. napus collectively known as canola or "double zero" were developed. The oil and residual meal from these cultivars were not pungent and had improved nutritional value. This resulted in a tremendous increase in rapeseed oil production in Europe and Canada, as the oil became fully interchangeable with other major edible vegetable oils and the meal became a substitute for soya bean meal. Present rapeseed production in northern Europe and central China is mainly based on biennial or winter types of B. napus, while summer types of B. rapa predominate in Canada and northern China where winters are severe. Brassica oilseed production in South Asia is based on annual B. rapa and B. juncea types, the latter covering 10-20% of the total production area.
The oil of canola rapeseed cultivars in Europe and Canada ("double zero") has a very low erucic acid and glucosinolate content and finds wide application as cooking oil and in the manufacture of margarine, shortening and other food products. However, in South Asia the unrefined oil of traditional rapeseed (B. rapa) and Indian mustard (B. juncea) cultivars is preferred as a cooking oil to the bland-tasting canola oil because of its flavour and pungency. The seed, especially that of B. juncea, is also used as condiment. After oil extraction, the cake or meal has a high protein content, but is unfit as feed for monogastric livestock unless derived from canola-type cultivars or treated by a rather expensive industrial process to remove the toxic glucosinolates. Cultivars bred for extra high erucic acid content in the oil are used for industrial purposes.
Different cultivars of these Brassica species are grown as leafy, stem and root vegetables, as well as forage and silage crops (see Prosea 8).
Production and international trade
The average annual world production of rapeseed during the period 1996-2000 was 36 million t, equivalent to 13.5 million t of oil, from 25 million ha in 51 countries. This represents a three-fold increase since 1980 and rapeseed is now the third most important source of vegetable oil after soya bean and oil palm. Leading rapeseed producers are the European Union (9.5 million t), China (9.2 million t), Canada (7.4 million t), India (5.0 million t) and Australia (1.5 million t). International trade in rapeseed oil amounts to 2 million t/year. Major exporters are Canada and the European Union, while practically the entire crop in China and South Asia is consumed domestically. About 12% of the total rapeseed meal (22 million t in 2000) was exported, mainly by Canada, China, eastern Europe and India.
Dried rapeseed contains per 100 g approximately: water 7 g, protein 22-25 g, oil 30-45 g, carbohydrates 24 g, fibre 2 g and ash 4-7 g. The energy value averages 2285 kJ per 100 g. The fatty acid composition of the oil of traditional cultivars of the 3 Brassica taxa is quite similar, and differences between cultivars of one cultivar group can be as large as differences between cultivar groups. The proximate composition of oil from traditional cultivars is: palmitic acid 2-4%, palmitoleic acid 0.2-0.5%, stearic acid 0.8-1.5%, oleic acid 8-33%, linoleic acid 12-21%, linolenic acid 8-14%, arachidic acid 0.5-1.2%, eicosenoic acid 6-12%, behenic acid 0-1%, erucic acid 25-55%, lignoceric acid 0-1% and nervonic acid 0-2%. Eicosenoic acid and erucic acid are long chain monoenoic acids that have anti-nutritional and toxic properties, and are associated with an increased risk of cardio-vascular ailments. Where these oils are traditionally used there is generally little awareness of the possible health risks, but the average daily intake per person of such oils is also low. The "double-zero" cultivars of both B. rapa and B. napus are low in eicosenoic acid (0.9-2.5%) and erucic acid (0.2-1.5%) but much higher in oleic acid (55-63%) and also higher in linoleic acid (20-24%) contents. The latest "triple-zero" cultivars also have a low linolenic acid content (3%) which improves the odour of the oil in cooking. The oil-free meal is rich in protein (36-44%) of a satisfactory amino acid composition, containing per 100 g protein approximately: lysine 6 g, methionine 2 g and cystine 2.5 g. The meal of such cultivars is suitable not only in ruminant feed, but also in pig and poultry feed, because the glucosinolate content is less than 10% of the 1-4% contained in traditional pungent rapeseed cultivars. Following disruption of cells during oil extraction or digestion, the glucosinolates are broken down by the enzyme myrosinase into glucose and isothyocyanates or nitriles, which may cause malfunction of the thyroid gland and consequently result in serious illness in humans and monogastric animals. When used as organic fertilizer the meal of high glucosinolate rapeseed cultivars has been found to reduce nematode infestations in the soil. The 1000-seed weight of all rapeseed cultivars ranges from 2-5 g.
- Annual or biennial herbs, 0.5-2 m tall.
- Taproot firm, 60-80 cm deep, numerous laterals in the top 30-50 cm of the soil; root system of B. napus and B. juncea more extensive than that of B. rapa.
- Stem erect or ascending, up to 2 cm in diameter, branched, greenish becoming yellow at maturity.
- Leaves bright to pale green, glabrous or slightly hairy; first true leaves pinnatifid, often with large apical lobe, petiolate, forming a rosette or on a short stem; leaves on flowering stems alternate, lanceolate, petiolate or sessile and clasping the stem, becoming smaller towards the top.
- Inflorescence an indeterminate raceme, 50-100 cm long, without bracts, borne terminally on main stem and branches; flowers tetramerous, bisexual; sepals erect, light green; petals yellow, spatulate, clawed; stamens 6, in 2 whorls, inner whorl of 4 long stamens, outer one of 2 short ones; nectaries 2, between the base of the ovary and the short stamens; ovary superior with false septum and 2 rows of campylotropous ovules, stigma globose.
- Fruit a silique, with convex valves, with indehiscent seedless beak, glaucous turning straw-coloured at maturity, 10-40 seeded.
- Seed globose, 1-3 mm in diameter; seed coat finely reticulate, yellow-brown, brown or black.
- Seedling with epigeal germination, taproot thin, cotyledons cordate.
- B. juncea: roots not tuberous; vegetative plant with rosette of leaves; basal leaves of flowering plant petiolate, with a very large terminal segment, highest leaves with short petiole; leaves bright green. Flowers with pale yellow petals, 7-10 mm long. Silique 3-5 cm long.
- B. napus: roots slender; vegetative plant with leaves on short stem; basal leaves of flowering plant petiolate, highest leaves sessile and partly clasping stem; leaves glaucous. Flowers with pale yellow to bright yellow petals, 11-15 mm long. Silique 5-11 cm long.
- B. rapa: roots tuberous; vegetative plant with rosette of leaves; basal leaves of flowering plant petiolate, highest leaves sessile and fully clasping stem; leaves bright green. Flowers with bright yellow petals, 6-10 mm long. Silique 4-7 cm long.
Growth and development
Properly dried Brassica seed will germinate within 2-4 days in moist soil, but freshly harvested seed may show slight dormancy. In annual rapeseed cultivars, flower initiation starts 2-6 weeks after seedling emergence and this is soon followed by rapid elongation of the main stem ("bolting"), flowering and seed set. In South Asia, the growth cycle from sowing to harvesting takes 75-100 days for B. rapa and about 4 months for B. juncea cultivars. In contrast, winter rapeseed cultivars of B. napus or B. rapa grown in north-western Europe have a crop duration of 10-11 months. They are sown in September with bolting starting in March, flowering in May and harvesting in July. B. rapa types are generally more winter-hardy than B. napus due to the leaf rosette formed in young plants which provides extra protection for the growing point against frost damage. Flowering starts at the base of racemes and may extend over a period of 3-5 weeks. B. rapa is allogamous with a sporophytic system of self-incompatibility, controlled by one locus with several S-alleles. Cross-pollination is effected by insects, mostly honey-bees. An exception is the autogamous B. rapa cv. group Yellow Sarson in South India. B. napus and B. juncea are self-pollinating, but up to 30% outcrossing may occur due to bees and other insects which are strongly attracted to rapeseed flowers. Under favourable growing conditions, about 50-70% of the flowers will set fruit with viable seeds. Seeds mature within 35-40 days after anthesis. Fruits of B. rapa are straw-coloured at maturity, while those of B. napus may still be greenish when containing fully ripe seeds. This is due to higher chlorophyll content in the fruit wall. Crop ripening follows the same pattern as flowering: from the base to the top of the plant.
Other botanical information
The genetic relationship between the six cultivated Brassica species is usually presented in a triangular diagram with the diploid species B. oleracea L. (2n = 16, BB genome), B. nigra (L.) Koch (2n = 18, CC) and B. rapa (2n = 20, AA) placed at the corners and the three allotetraploid species on the sides. B. carinata A. Braun (2n = 34, BBCC) probably arose from natural interspecific hybridization between B. nigra and B. oleracea, B. juncea (2n = 36, AABB) between B. rapa and B. nigra, and B. napus (2n = 38, AACC) between B. rapa and B. oleracea. Recent work with molecular markers has provided further evidence of this relationship.
B. carinata (Abyssinian mustard, Ethiopian mustard, gommenzer) is only known from cultivation in Ethiopia and northern Kenya; a cooking oil is extracted from the seeds, the cake is used as a medicine, crushed seeds are consumed in soups or as spice and leaves are also eaten as a vegetable. The plants reach a height of up to about 2 m; basal leaves of flowering plants are petiolate, highest leaves sometimes subsessile; leaves light green; flowers with bright yellow petals, 6-10 mm long; silique 2-6 cm long. In Ethiopia annual seed production is estimated to be 20 t. In other parts of the world, e.g. in Canada, B. carinata is becoming more popular and is considered a promising oilcrop.
Rapeseed crops are cultivated between 60 °N and 40 °S in temperate climates, at 1500-2000 altitude in the tropics and during the cool season in the subtropics. Optimum temperatures for growth and seed set are 18-25 °C. Winter types of B. napus and B. rapa are resistant to frost down to -10 °C at the early vegetative stage. This allows sowing to be done in autumn where moderate winters prevail. For these cultivars, low temperatures are needed for vernalization. Extended periods at 30-35 °C or higher during flowering and seed set have a negative effect on yield and oil content. Photoperiodic requirements of B. napus and B. rapa cultivars vary greatly from 10 to over 20 hours and some are day-neutral. Cultivars tend to be locally adapted and may not reach maturity outside their normal photoperiodic range. Water requirements for satisfactory yields are 400-500 mm, mainly during the vegetative and flowering periods. In the subtropical regions of South Asia, B. juncea and B. rapa are grown during the dry and cool winter ("rabi") season on residual soil moisture after the monsoon crops. Rapeseed can be grown on a wide range of soils, provided these are free-draining because even short periods of waterlogging are detrimental to young crops. A pH of 6.5-7.6 is suitable for optimum growth. Rapeseed tolerates a fair amount of salinity.
Propagation and planting
Rapeseed retains a high viability for more than 4 years when stored dry (6% moisture content) and cool (below 18 °C). Rapeseed is sown directly in the field either by manual broadcasting or machine-drilling in rows 20-45 cm apart, at seed rates of 5-9 kg/ha. The seed rate and spacing may be varied considerably without a significant effect on yield, because rapeseed has a considerable ability to compensate for irregular plant stand by increasing branching. Optimum seedling density is about 160 plants per m2, while optimum final plant density is 60-80 plants per m2. Since seeds are small, the seed bed should be well prepared, level and free of weeds. Recommended planting depth is 0.5-2 cm, depending on soil type and cultivar. The time of sowing is important; late sowing is detrimental to growth and production for rapeseed grown in summer at higher latitudes or during the cool season in the subtropics. Early sowing may also reduce flea beetle damage but early sowing of winter rapeseed increases the risk of frost damage. In the United States, canola is sown about 6 weeks prior to the anticipated onset of hard frost to ensure that seedlings have 6-8 leaves and a well-developed crown prior to the onset of severe weather. On the alluvial plains of South Asia, B. juncea is sometimes sown under zero-tillage conditions in lowland fields just before or immediately after the rice harvest.
Weed control in rapeseed crops is very important during early establishment. Two rounds of hand weeding or mechanical weeding are usually sufficient. Once stems begin to elongate and branch, weeds are effectively suppressed. Rapeseed is very sensitive to most herbicides, including pre-emergence ones. When soil moisture or rainfall becomes deficient, supplementary irrigation shortly before flowering and another application during seed filling can produce economic yield increases. Rapeseed can produce reasonable yields on soils with low nutrient status, but it responds well to organic or chemical fertilizers, particularly N. Rapeseed is rarely fertilized in South Asia, but it may benefit from residual nutrients of the previous crop. A typical fertilizer recommendation for an intensive summer rapeseed crop with a seed yield of over 2 t/ha is: N 40-50 kg, P 50-60 kg and K 25-30 kg per ha in the seed-bed and another 40-50 kg N as top dressing before flowering. Boron deficiency can be rectified by applying B fertilizer 1-2 kg/ha. Rotation with rapeseed is known for its beneficial phytosanitary effect on cereals, but it may also cause a problem of volunteer seedlings in the consecutive crop. Seed set and consequently yields are often improved considerably by placing beehives near flowering rapeseed fields, normally at a rate of 7-10 hives per ha. The resulting honey production provides an additional source of income.
Diseases and pests
More than 15 diseases are common to rapeseed. Widespread diseases, which sometimes cause severe crop losses include leaf spot (caused by Alternaria brassicae ), blackleg (caused by Leptosphaeria maculans, syn. Phoma lingam), stem rot (caused by Sclerotinia sclerotiorum), clubroot (caused by Plasmodiophora brassicae), white rust (caused by Albugo candida) and black rot (caused by Xanthomonas campestris). Some of the measures that reduce disease incidence are crop rotation, fungicidal sprays and disinfection of seeds before sowing.
Numerous insect pests are known to attack rapeseed from young seedlings to the mature crop but occurrence and the degree of damage vary considerably between continents and regions. The most damaging pests are pollen beetles (Meligethes spp.), seed-pod weevils (Ceutorhynchus spp.), flea beetles (Phyllotreta spp.), aphids (e.g. Brevicoryne brassicae), armyworm (Spodoptera exigua) and diamond-back moth (Plutella xylostella). Insecticidal sprays toxic to bees and other pollinating insects should be avoided during flowering of rapeseed fields.
Other important pests are nematodes (Meloidogyne spp., Pratylenchus spp. and Heterodera spp.) and the parasitic broomrape (Orobanche spp.). Crop rotation with non-Brassica crops is the only practical means of reducing infestation.
Signs of maturity of rapeseed crops are the yellowing of stems and pods, rattling sound of fruits when shaken and dark colour of the seeds. Harvesting is best done before the whole crop is fully mature to avoid yield loss due to seed shattering and a deterioration in quality. Therefore, further drying is needed before threshing to separate the seed from the fruits. Manually harvested rapeseed is usually spread on a threshing floor to dry in the sun before threshing. For the same reason, machine harvesting is often followed by windrowing to dry the crop before threshing.
World average yield of rapeseed is about 1.4 t of seeds per ha while that from smallholders in India or China is often not more than 500-800 kg/ha. Spring-sown rapeseed on large-scale farms in the Canadian prairies and Australia produce 900-1600 kg seeds/ha while winter rapeseed crops of Europe yield 2000-4000 kg seeds/ha.
Handling after harvest
The high oil content and small seed size require rapeseed to be handled efficiently and to be dried to 6-8% moisture content to prevent rapid deterioration in quality. Clean and dry rapeseed stores well for at least one year. In South Asia, about 30% of the rapeseed is still processed in small-scale oil mills that are bullock-driven or power-driven pestle and mortar devices called "ghanis". Much of the rapeseed oil produced in this manner is sold unrefined, sometimes after filtration. This type of crude oil has a pungent flavour and a rather dark colour due to the seed coat pigments. The oil from 70% of the crops is extracted in larger mills by mechanical expellers or by solvents. Advanced rapeseed processing involves several steps, including cleaning, flaking and cooking, oil extraction by screw press or by solvent or by a combination of both, filtration and refining through degumming, de-acidification, bleaching and deodorization. The resulting oil is light coloured and has a bland taste. The meal obtained after oil extraction of canola-type rapeseed cultivars can be used to prepare various products for the stock-feed industry, e.g. protein concentrates and isolates.
Germplasm collections of Brassica oilseed are maintained by agricultural institutes in Europe, Canada, the United States, India, Japan and China. The International Plant Genetic Resources Institute (IPGRI) in Rome keeps a database on global resources for Brassica species. The possibility of interspecific hybridization, aided by embryo culture, in vitro fertilization and protoplast fusion, allows the exploitation of the large genetic diversity present in certain species, notably B. juncea, B. oleracea and B. rapa for the improvement of oilseed crops. This applies particularly to B. napus because genetic variation in this species is rather limited.
Common methods of developing improved cultivars from available landraces have been recurrent mass and family selection in case of the outcrossing B. rapa and pure line and pedigree selection for the self-pollinating B. juncea and B. napus. Breeding objectives are higher seed yield and increased oil content, reduced seed shattering, shorter and more erect plant habit, environmental adaptation, especially cold tolerance in Europe, earlier maturity in India and tolerance to stress and salinity. Further objectives include thinner seed coat resulting in less crude fibre in the meal and resistance to important diseases and pests. Better knowledge of the chemical components of the oil and their genetic control, as well as the development of analytical techniques applicable to single seeds without impairing viability, has resulted in considerable advances in breeding for higher seed and oil quality. Low erucic acid content is controlled by two recessive genes with additive effects, low glucosinolate content by at least three genes and low linolenic acid content by one gene. The "double-zero" and "triple-zero" or canola cultivars were developed by introgression of these characters through backcrossing into existing cultivars, and they have dominated rapeseed production in Europe, Canada and Australia since the 1980s. During the last decade, F1canola hybrids have started to replace open-pollinated cultivars. There is considerable hybrid vigour for seed yield (20-70%) in B. rapa, as well as in B. napus, particularly between parents of diverse origin. In vitro anther or microspore cultures to produce haploids for instant inbred lines is more successful in B. napus than in B. rapa. Large-scale production of F1hybrid seed is based on self-incompatibility or cytoplasmic male sterility (CMS) with fertility restorer genes. Sources of CMS systems are interspecific crosses, protoplast fusion and recently, also genetic transformation. The transgenic systems of CMS are claimed to be free from the persistent problems of poor growth caused by chlorosis and low female fertility linked to the other systems. Resistance to herbicides, especially atrazine, which is an important cost-reducing factor in rapeseed production, was successfully introgressed into B. napus and B. rapa cultivars from Bird’s rape, which is a wild form of B. rapa. Transgenic canola rapeseed cultivars with resistance to glyphosate or glufosinate herbicides have become available recently as well.
Daylength-neutral B. napus cultivars suitable for cultivation during the short-day, cool season of the subtropics have been developed by introgression of photo-insensitivity from other Brassica species into B. napus. Such cultivars are higher yielding than local B. rapa landraces and also more tolerant of temporary waterlogging.
The present trend of expanding rapeseed production is likely to continue, particularly in India and China, where canola-type cultivars will also gradually replace the traditional, high erucic acid and high glucosinolate landraces. The remaining technical problems of hybrid seed production should be solved soon and F1 hybrid cultivars will then dominate in most rapeseed-producing countries on account of their considerably higher yield potentials, with the possible exception of smallholder production systems of South Asia where the pungent oil is preferred. Molecular breeding technology is well advanced in rapeseed, which offers opportunities for rapid gene transfer from unrelated species with regard to host resistance to important diseases, pests and weeds and also for the production of novel industrial oil and pharmaceuticals.
Rapeseed cultivars developed in South Asia, especially the day-neutral B. napus types, may fit well into existing cropping systems in the tropical highlands of South-East Asia.
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