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Sovero, M. 1993. Rapeseed, a new oilseed crop for the United States. p. 302-307. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.

Rapeseed, a New Oilseed Crop for the United States

Matti Sovero

    1. Taxonomy
    2. Origin
    1. Heat Tolerance
    2. Cold Tolerance
    3. Vernalization Requirement
    4. Site Selection and Cultural Practices
    1. Canola Oil
    2. High Erucic Acid Rapeseed (HEAR) Oil
    3. Rapeseed Meal
    1. Canola
    2. High Erucic Acid Rapeseed (HEAR)
    3. Specialty Oils
    4. Adaptation

Rapeseed is the third most important source of vegetable oil in the world, after soybean and palm oil. During the past twenty years, it has passed peanut, cottonseed, and most recently, sunflower, in worldwide production. This is almost entirely due to the plant breeding work initiated in Canada in the 1950s and 1960s which greatly reduced the levels of two anti-nutritional compounds, erucic acid in the oil and glucosinolates in the meal, creating a new, high-value oil and protein crop known as canola in Canada and the United States. Although rapeseed has been domestically grown since World War II, it gained wider interest only after canola oil was granted GRAS status in 1985. Canola is the Canadian Canola Association trademark which refers to any rapeseed with less than 2% of erucic acid (C22:1) in the oil and less than 30 umol of the four major aliphatic glucosinolates in a gram of air dry solids. This definition will be changed in 1995 so the limit will be 15 µmol of glucosinolates. In addition to aliphatic glucosinolates, defatted rapeseed contains usually approximately 5 µmol/g of another group of glucosinolates called indolyls.

Double low rapeseed, as defined by European Community standards, has less than 35 µmol of total glucosinolates tel quel. This definition will also change in 1992 with only 20 µmol of total glucosinolates being allowed after 1992. This change will bring the European and Canadian definitions of canola very close to each other.

The term "industrial rapeseed" does not have any regulatory basis but refers to any rapeseed with a high content of erucic acid in the oil. For most purposes, the limit is 45%, although higher contents are considered desirable. The term "single low" refers to high glucosinolate rapeseed with low erucic oil. High erucic cultivars with low glucosinolate content also exist.

The estimated domestic need for canola oil in 1995 is one million tons. The domestic production of this would require 1 million to 2 million hectares. Increased interest in edible rapeseed production has also resulted in renewed interest in production of high erucic rapeseed for industrial purposes.


Rapeseed is derived from two Brassica species, B. napus L. and B. rapa L. To distinguish between them B. rapa is often called turnip rape and B. napus is called Swede rape. Spring and winter types exist of both species. The rapeseed oil of world commerce comes from these two species and to a minor extent also from the mustards, especially B. juncea Coss. (brown mustard) and Sinapis alba. L. (yellow mustard).


In addition to B. napus L. and B. rapa L., Brassica includes cultivated species B. carinata Braun (Abyssinian mustard), B. nigra Koch, and B. oleracea L. The four most widely cultivated species, B. juncea, B. napus, B. oleracea, and B. rapa are highly polymorphic including oilseed crops, root crops, and vegetables such as Chinese cabbage, broccoli, and Brussel sprouts.

The relationships among the cultivated species were largely clarified by cytological work of Morinaga (1934). According to his hypothesis, the high chromosome number of species B. napus (2n = 38, AACC), B. juncea (2n = 36, AABB), and B. carinata (2n = 34, BBCC) are amphidiploids combining in pairs the chromosome sets of the low chromosome number species B. nigra (2n = 16, BB), B. oleracea (2n = 18, CC), and B. rapa (2n = 20, AA). This hypothesis was verified by U (1935) with successful re-synthesis of B. napus. Re-synthesis of B. juncea and B. carinata was accomplished later by Frandsen (1943, 1947). The low chromosome number species may have developed from ancestral species with even lower chromosome numbers as suggested by Robbelen (1960).


Brassica crops may be among the oldest cultivated plants known to man. In India, B. rapa is mentioned in ancient Sanskrit literature from ca. 1500 BC and seed of B. juncea have been found in archaeological sites dating back to ca. 2300 BC (Prakash 1980). Rapeseed production has a long history in China. The Chinese word for rapeseed was first recorded ca. 2500 years ago, and the oldest archaeological discoveries may date back as far as to ca. 5000 BC (Yan 1990).

Historically, B. rapa seems to have the widest distribution of Brassica oilseeds. At least 2000 years ago, it was distributed from northern Europe to China and Korea, with primary center of diversity in the Himalayan region (Hedge 1976).

Brassica napus has probably developed in the area where the wild forms of its ancestral species are sympatric, in the Mediterranean area. Wild forms of B. napus are unknown, so it is possible it originated in cultivation. Production of oilseed B. napus probably started in Europe during the middle-ages; B. napus was introduced to Asia during the 19th century. The present Chinese and Japanese germplasm was developed crossing European B. napus with different indigenous B. rapa cultivars (Shiga 1970).


World rapeseed production exceeds 20 million hectares, making it the third most important oil plant in the world after palm oil and soybean. The leading producers in 1991 were China, India, European Community, and Canada with estimated areas of 6.13, 6.10, 2.43, and 3.14 million hectares, respectively (Oil World Statistics Update 1992). The European Community figure includes only the major producers Denmark, France, Germany, and U.K. and would be somewhat higher if smaller producers such as Italy and Spain were included. Because of its high yields, European Community was the leading producer of rapeseed oil in 1991.

Winter type B. napus is the main rapeseed crop in most of Europe, in parts of China and also in the eastern United States. Spring type B. napus is produced in Canada, northern Europe, and China. Where winters are mild enough (e.g. southeastern United States) spring type B. napus can be grown in the fall. In the future we should see distinct varieties developed for these areas.

Spring type B. rapa occupies approximately 50% of the Canadian rapeseed area and is also grown in northern Europe, China, and India. Winter type B. rapa has largely been replaced by more productive winter type B. napus and spring crops in its traditional production areas and has no significant impact on the world's rapeseed production at the present.

Only spring types exist of B. juncea. It is the leading Brassica oilseed in India and also produced in Canada and Europe but only for condiment use. Recently, low erucic, low glucosinolate types of B. juncea have been developed and it is possible that in the future it will be an important oilseed crop for the more arid areas of Canada and the northern United States.

The transition from high erucic to low erucic rapeseed, and the simultaneous rapid growth in the global rapeseed production began in Canada in 1968, with commercial release of single low cultivar 'Oro' followed by several other single low cultivars and the first canola Cultivar 'Tower' in 1974. In Europe, the transition started later with the release of the first single low cultivars in 1974. Almost all rapeseed produced in Canada and Europe is canola. The introduction of low erucic rapeseed is now underway in China and India.

This change in crop quality has created a need for specialized production of industrial rapeseed. Improved cultivars for this purpose have been developed in Canada, the United States and now in Europe. Because of the relatively small demand for high erucic oil and, consequently, for industrial rapeseed in comparison with edible rapeseed, most plant breeders now work exclusively on canola. This has led to a shortage of competitive new industrial rapeseed cultivars and, consequently, complicated industrial rapeseed production further.


Heat Tolerance

Rapeseed grows best in mild maritime climates. Historically, the highest rapeseed yields have been produced in England and the Netherlands, a phenomenon which has more to do with climate and soil conditions than sophisticated crop management.

The growth of rapeseed is most vigorous in temperatures between 10° and 30°C with the optimum around 20°C. Rapeseed is very sensitive to high temperatures at the blooming time even when ample moisture is available. Long periods of over 30°C can result in severe sterility and high yield losses. During the pod-filling period rapeseed is somewhat more tolerant to high temperatures. The seed oil content, however, is highest when the seeds mature under low temperatures (10° to 15°C). Extended periods of high temperature during the seed-fill period invariably result in low oil contents and poor seed quality.

Cold Tolerance

The rapeseed plant's ability to tolerate low temperatures depends essentially on its development and the degree of hardening it has achieved. Unhardened plants can survive -4°C, while fully-hardened spring type rapeseed can survive -10deg. to -12°C. Hardened winter rapeseed can survive short periods of exposure to temperatures between -15° and -20°C. Dehydration during sunny and/or windy days while the soil is frozen can cause extensive winter kill in much higher temperatures even when the plants are optimally developed and fully hardened.

The hardening requirements of rapeseed have not been fully characterized. Some time in temperatures below 10°C is, however, typically required. Winter types tend to harden faster, achieve higher degree of cold tolerance and unharden slower than spring types (Paul Raymer pers. commun.), but it is likely that variable hardening requirements could also be found within both types. Some differences in cold hardiness have been observed among both winter spring types. Whether these are due to differences in ultimate achievable cold hardiness or differences in hardening requirements only is unclear.

The plants are typically best adapted to survive the winter in rosette stage with 6 to 8 leaves. Smaller plants are usually not as capable of surviving over-wintering, while plants with more leaves often start the stem elongation prematurely, exposing the meristem tissue to cold, making it more susceptible to damage.

Unhardening happens fairly fast after the plants initiate active growth. Winter type rapeseed can generally still survive temperatures down to 12°C just before the blooming begins (Cramer 1990).

Winter survival is greatly reduced by environmental factors such as occurrence of diseases and pests, grazing, inadequate, excessive or unbalanced soil fertility, and poor drainage conditions. The absence of snow cover during the coldest period of the winter decreases the plants' chances to survive. Ice formation on the soil surface can damage the crown area of the plants and reduce survival rate.

Vernalization Requirement

Most winter rapeseed cultivars will require three weeks of near-freezing temperatures in the field to get fully vernalized and start rapid generative growth. In controlled environments, eight weeks at 4°C temperature is sufficient for full vernalization. In spring planting, winter rape will typically start slow generative growth after the prolonged rosette stage, and some cultivars may start blooming towards the end of the growing season. Differences in this respect are sometimes useful in distinguishing between similar cultivars. Differences in vernalization requirements are apparent among winter rape cultivars.

Some spring type cultivars do not exhibit any vernalization response at all, but in some cases the generative development can be accelerated with brief chilling treatment. In spring planting, only a few cool nights are usually needed for this. Vernalization response in spring types also tends to disappear in a long day environment (Raymer pers. commun.). In spite of the variability in vernalization requirements within both types, the differences between the types are fairly clear with no overlap in the initiation of blooming in either spring or fall planting.

A high vernalization requirement does not necessarily result in good winter hardiness, as many of the winter type cultivars from extreme maritime environments, such as Japan, require a long vernalization period yet have little tolerance for low temperatures.

Site Selection and Cultural Practices

Good drainage is an essential. Winter rape in particular has little tolerance for heavy, wet soils and a high water table. Wet soil can significantly reduce winter survival and contribute to root disease. Establishment of uniform stands is often difficult in heavy soils. Rapeseed grows best in sandy loams, loams with high organic matter, and loamy sands. Light soils are acceptable, and even ideal when adequate moisture and nutrients are available. Boron deficiency can cause significant yield losses even if no morphological deficiency symptoms are visible.


Canola Oil

Well-developed rapeseed seed contains 40 to 44% oil. The fatty acid composition of the oil is genetically more variable than probably the composition of any other major vegetable oil. Canola oil today contains only traces of erucic acid, 5 to 8% of saturated fat, 60 to 65% of monounsaturated fats, and 30 to 35% of polyunsaturated fats. Mutants with significantly elevated monounsaturate levels exist.

Canola oil is widely used as cooking oil, salad oil, and making margarine. Of all edible vegetable oils widely available today, it has the lowest saturated fat content, making it appealing to health-conscious consumers. Its use in continuous frying and some other industrial uses is somewhat limited by its high linolenic acid (C18:3) content (usually 8 to 12%) and, consequent, fairly high oxidation tendency. Mutant materials with only 2 to 3% of linolenic have also been developed.

The use of canola oil in non-edible uses has been studied fairly extensively and it is at the present used to some extent in lubricants and hydraulic fluids especially when there is a significant risk of oil leaking to water ways or to ground water.

High Erucic Acid Rapeseed (HEAR) Oil

High erucic rapeseed oil is used in lubricants, especially where high heat stability is required. Because of its high polarity, uniform molecule size, and long carbon chains it has greater affinity to metal surfaces and better lubricity than mineral oils. It is easily biodegradable which makes it especially appealing in environmentally sensitive uses. Although HEAR oil in many applications is superior to vegetable oils with shorter average fatty acid chain length, such as canola, it can sometimes be replaced by these. The surplus of low erucic oil in European Community countries has especially increased industry's interest in Europe to use it in place of HEAR oil. This situation has also increased public interest in promoting the production of industrial rapeseed to lower the surpluses of low erucic rapeseed.

In the oleo-chemical, industry high erucic oil is used as a source of erucic acid to produce a slipping and anti-blocking agent used in plastic foils, foaming agents used for instance in mining industry, and many other chemicals for both food and non-food industries. The long chain length of erucic acid makes it a unique raw material in oleo chemical industry. Although in some oleo chemical processes it is virtually irreplaceable, the total demand for erucic acid is fairly low and not expected to grow radically in the near future. Most likely, growth rate is approximately equal with the general growth of oleo chemical industry, which again, as typical for mature industries, is likely to be approximately equal with the overall economic growth.

Significant changes to this scenario will depend on inventions and technical breakthroughs which defy prediction. There is, however, a trend visible that is likely to work in favor of increased use of high erucic oil in future, both in oleo chemical and other uses. The development of "green technology" with increased emphasis on renewable resources and biodegradability is likely to increase interest in raw materials such as high erucic oil.

Rapeseed Meal

Rapeseed meal contains approximately 40% of protein which rates among the nutritionally best plant proteins. For monogastric diets it has better amino acid balance than soybean meal.

In traditional rapeseed cultivars the seed solids contained over 100 µmol/g of glucosinolates. The hydrolysis products of glucosinolates give cruciferous vegetables their characteristic flavor and mustard it's pungency. Some of these hydrolysis products, however, are toxic or at least anti-nutritional. Also, many of the glucosinolate derivatives decrease the palatability of the meal and, consequently, the voluntary uptake of the feed by animals. For these reasons, the use of conventional rapeseed meal was limited mainly to cattle supplementary protein formulas and had relatively low value.

With the quality of canola, significant amounts of meal can be used in virtually all animal feeds and economical disposal of the crushing residue is typically not a problem. Since some of the glucosinolates are destroyed in the crushing process, the meal of future canola cultivars will be almost glucosinolate free and can be used in feed formulas without any special limitations.



The canola industry in the United States was created after 1985 when canola oil was granted GRAS status. At present, most major food processors are using canola oil. This year the estimated imports will reach 300,000 t, while the domestic production is approximately 50,000 t.

The estimated need for canola oil in the United States by 1995 is approximately one million tonnes. The domestic production of this would require 1 million to 4 million hectares of rapeseed, depending on the production areas and cultivar types. As the by-product of the oil approximately 1.5 million tonnes of rapeseed meal would be produced. If the meal is of canola quality it should be easily absorbed by animal feed industry without burdening the crush margins for canola.

High Erucic Acid Rapeseed (HEAR)

The present consumption of HEAR oil in the United States is approximately 10,000 to 15,000 t/year. Dramatic changes in consumption are not likely to occur in the near future, although steady growth can be expected. Even if all HEAR oil will be produced domestically, and only using rapeseed, high erucic rapeseed will not develop into a major field crop in the foreseeable future, but it will remain a specialty crop for limited productions areas.

Specialty Oils

Several biotechnology companies are working to develop rapeseed with altered seed composition. Potential products could include crops which will replace foreign sources of oils and fatty acids or even produce chemicals currently for which economical plant sources are not available. The impact of these developments on the total rapeseed production is unpredictable, but it is possible that if at least some of these projects are successful, specialty rapeseed in the future will have at least as much area in the United States as canola.


Since little breeding work was done in the United States prior to 1985, production has mainly been based on imported cultivars, although the cultivar 'Cascade' from the University of Idaho has been grown to some extent in the Midwest and Pacific Northwest. In the summer of 1990, two cultivars 'A112' and 'A114' from Calgene/Ameri-Can's breeding program were also introduced to the market in the Southeast and have since been widely accepted to production.

Early Canadian spring types, both B. napus and B. rapa, can be produced in the northern tier states, although aridity and high summer temperatures will set limits to their adaptation. The best production areas will probably be in the western and eastern ends of the range which form the southern extensions of the "Canola Crescent" of the Canadian prairies. European winter rapeseed cultivars can also be grown successfully in the Pacific Northwest in the areas where winters are not too harsh and adequate fall moisture is available.

The Midwest, extending from central Indiana and Ohio to Central Michigan, may be the best region for the production of European type winter rapeseed cultivars, although they can be produced profitably as far south as northern Georgia. Further south, these cultivars do not reach adequate vernalization but will be extremely late if they produce any generative growth at all.

In the Great Plains area, rapeseed could possibly be grown in at least Texas, Oklahoma and parts of Kansas. Production has, to-date, suffered from multiple problems. Because of the extreme summer heat only winter rapeseed can be grown, yet the winter hardiness of present winter rape cultivars are only marginal for the region. Even if winter survival can be improved to some extent with proper cultural methods, significant genetic improvement is needed before rapeseed can be introduced to wide scale production in the Great Plains. Cultivars for this area need to be earlier than what is presently available to avoid the hot, dry summer weather which will ripen the plant prematurely and also cause extensive shattering losses.

In the Southeast, rapeseed has been very successful in the southern parts of Georgia and also in South Carolina. European spring type cultivars are well adapted to winter production in this area. Most of them have adequate winter hardiness and since they typically start blooming somewhat later than Canadian cultivars, they mostly escape the damage from spring frosts. There are regions in the Southeast where winter and spring types produce very similar yields. In those areas, however, spring cultivars typically will mature 10 to 14 days before winter cultivars and may be more appealing to producers for this reason.

Although imported cultivars have so far been fairly successful, the development of domestic, regionally-focused breeding programs is very important for the growth of rapeseed industry in the United States. In introducing rapeseed to double-cropping rotations, the lack of a high-yielding, early-maturing winter type has been a problem, and suitable cultivars need to be developed in America. It is likely that differences in cropping systems and climate will ultimately give domestic breeding programs an advantage. Imported cultivars will gradually disappear from the market once rapeseed gets established and the germplasm development in the United States starts producing results.

The development of pest and disease management strategies and availability of suitable chemicals and/or resistant cultivars is also an important factor affecting the acceptance of rapeseed to production in the United States. Diseases such as white mold, black spot, and blackleg have caused significant damage in some areas. Although the incidences have so far been isolated, the disease problem can only grow worse as production expands unless control methods become available. Cabbage seed pod weevil has established itself as a major problem in areas where rapeseed has several years of history in cultivation, and other insect pests are likely to emerge.


Last update April 15, 1997 aw