Linum usitatissimum (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Cereal / pulse|
|Forage / feed|
- Protologue: Sp. pl. 1: 277 (1753).
- Family: Linaceae
- Chromosome number: 2n = 30
- Linseed, flaxseed, flax (En).
- Lin (Fr).
- Linhaça, linho (Po).
- Kitani (Sw).
Origin and geographic distribution
Linum usitatissimum most likely evolved by domestication from wild Linum bienne Mill. (‘pale flax’), a short-lived perennial which occurs in western and southern Europe and western Asia. India is an important centre of genetic diversity for Linum usitatissimum, but cannot be considered the centre of origin because of the absence of its progenitor Linum bienne. Linum usitatissimum was among the first crops to be taken into cultivation in the Fertile Crescent more than 8000 years ago. It developed into a fibre crop, called ‘fibre flax’ and an oilseed crop, called ‘linseed’. Archaeological evidence indicates that the domestication and early distribution of cultivated flax occurred principally as a fibre crop, but this may be due to the fact that textiles are more easily preserved than oil. Flax provided the fibres for cloth and cordage of the Sumerians, Egyptians, Greeks and Romans. It was traded by the Egyptians by 4000 BC and remnant seed has been found in prehistoric settlements in the Swiss Alps. The high oil content of the seed was also appreciated and Egyptian mummies provide evidence of the use of the oil by 1400 BC. Specialization occurred early: Mediterranean and European types developed into fibre flax; short-season types adapted to the warmer climates of western Asia, the Indian subcontinent and Ethiopia developed into linseed types.
Linum usitatissimum is now grown widely in many parts of the world, including the tropics. Fibre flax is cultivated in cool and humid temperate climates, whereas linseed is grown in warmer climates. Socio-economics also affect the distribution; Eastern Europe and the Russian Federation produce mainly fibre flax, Canada and the northern United States mainly linseed. In tropical Africa linseed production is concentrated in the Ethiopian highlands, where linseed has been grown since time immemorial. At higher altitudes it is the second most important oil crop after niger seed (Guizotia abyssinica (L.f.) Cass.). Linseed is also grown on a small scale in the other highlands of East Africa. Fibre flax has commercially been grown in Kenya and Uganda.
Linum usitatissimum is grown for its oil-rich seeds and bast fibre, as distinct or dual purpose crops. There is a long tradition of consuming linseed, usually in a mix with cereals, in western Asia and the Indian subcontinent. In Europe and North America linseed is nowadays a standard ingredient in health foods such as multi-grain breakfast cereals and breads. In Ethiopia the seed is commonly roasted, ground and mixed with spices and some water to be served along with local breads. It is also consumed in soups, soft drinks and with porridges or cooked potatoes.
The oil develops a very unpleasant rancid flavour soon after seed crushing and oil extraction, making it less suitable for human consumption. This is associated with the high content of linolenic acid and rapid oxidation at the double bonds. Eventually, the oil polymerizes into a flexible film. Traditionally it has found wide application as drying oil in paints, varnish and industrial coatings, lamp oil and in the manufacture of window putty, soaps, printing ink, erasers and linoleum, as well as waterproofing for raincoats and tarpaulins. Edible linseed oil with only a few percent linolenic acid and much higher linoleic acid content is produced from ‘Solin’ or ‘Linola’ cultivar types recently developed in Canada and Australia. Seed mucilage is used as a substitute for gum arabic as a stabilizer, binder, gelling and suspension agent in foods. It has been patented as an egg-white substitute. Linseed cake and meal after oil extraction are used as a supplement of protein and omega-3 fatty acid in livestock feeds after prior removal of toxic substances. They are especially used to increase the omega-3 content of chicken egg and pork meat.
The traditionally highly valued medicinal properties of linseed have regained considerable interest in recent times. The seeds or their biologically active constituents (soluble and insoluble dietary fibre, α-linolenic acid and lignans) are used in nutraceuticals to alleviate various ailments, such as digestive complaints, high blood cholesterol, coronary and kidney diseases, hormonal problems and certain types of malignant tumours.
Linen woven from the bast fibre is used for household textiles (towels, table cloths etc.), furnishings (curtains, wall coverings and upholstery fabrics) and clothing. Its high moisture absorption, strength, launderability, excellent colour fastness and resistance to shrinkage make it well suited for these purposes. A disadvantage is that it creases easily. The fibre is also used in the manufacture of fine papers such as cigarette, art, currency, archival and security papers, often in blends with other pulps. The flax fibre used for paper is derived from waste material from spinning and weaving mills, linen rags, the short bast fibre fraction or waste product left over from the processing of high quality textile fibre (‘flax tow’), or mechanically decorticated straw of flax that has been grown primarily for seed (‘seed flax tow’).
Straw from the linseed crop is also utilized in the manufacture of twine, bagging and insulating wallboards. The woody core left after fibre extraction is used in the manufacture of chipboard or, in combination with bast fibre, for paper making.
Production and international trade
The average annual world production of linseed in 2004–2008 was about 2.2 million t from 2.5 million ha. The main producers were Canada (798,000 t), China (407,000 t), United States (268,000 t), India (174,000 t), Ethiopia (136,000 t) the Russian Federation (73,000 t), United Kingdom (48,000 t) and France (41,000 t). The average annual linseed exports in 2004–2008 were 987,000 t, with a value of US$ 429 million. Canada was the largest exporter of linseed ( 634,000 t/year), Belgium the largest importer (over 400,000 t) and the second largest exporter (138,000 t). Exports of linseed from tropical African countries were negligible.
The average annual world production of linseed oil was 648,000 t, with as main producers China (139,000 t/year), the United States (130,000 t) and Belgium (112,000 t). Ethiopia produced 46,000 t linseed oil per year. Annual world exports of linseed oil in 2004–2008 averaged 226,000 t, with a value of US$ 224 million. The main exporters were Belgium (89,000 t/year) and the United States (40,000 t), the main importers the Netherlands (43,000 t) and Germany (40,000 t).
The annual world production of flax (fibre and tow) in 2004–2008 was 730,000 t from 413,000 ha, major producers being China (460,000 t), France (93,000 t), the Russian Federation (50,000 t) and Belarus (47,000 t). The average annual flax (fibre and tow) exports in 2004–2008 amounted to 210,000 t, with a value of US$ 379 million. The principal exporters were France (94,000 t/year) and Belgium (63,000 t/year), the main importing countries China (89,000 t/year) and Belgium (32,000 t/year).
The seed contains per 100 g edible portion: water 7 g, energy 2236 kJ (534 kcal), protein 18.3 g, fat 42.2 g, carbohydrate 28.9 g, total dietary fibre 27.3 g, Ca 255 mg, Mg 392 mg, P 642 mg, Fe 5.7 mg, Zn 4.3 mg, thiamin 1.6 mg, riboflavin 0.16 mg, niacin 3.08 mg, folate 87 μg, ascorbic acid 0.6 mg (USDA, 2011). The fatty acid composition of the oil in traditional linseed is: palmitic acid 5–6%, stearic acid 4–5%, oleic acid 18–20%, linoleic acid 14–16%, α-linolenic acid 40–60%. In the oil of ‘Solin’ and ‘Linola’ cultivar types, the linolenic acid levels can be as low as 2%, with a concomitant increase of linoleic acid, while the level of other fatty acids remains unaltered.
The mucilage of linseed consists mainly of soluble dietary fibre, which is composed of polysaccharides, polypeptides and glycoproteins. The ratio of soluble to insoluble dietary fibre in linseed varies from 1:4 to 2:3. The significant reduction in total and LDL cholesterol and in blood glucose associated with regular linseed consumption is attributed to the mucilage. Linseed also improves bowel movement: the mucilage absorbs water from the gastro-intestinal tract, while the insoluble fibre increases stool transit time. The α-linolenic acid is an essential, omega-3 fatty acid in the human diet. It is involved in increasing the activity of membrane-bound phospholipids, enhancing the elasticity of arterial membranes and reducing eicosenoids-mediated inflammatory reactions leading to arteriosclerosis and rheumatoid arthritis. Linseed is rich in plant lignans (diphenolic compounds), which are converted to mammalian lignans in the colon. Lignans inhibit cell proliferation and growth. They have been shown to be effective against hormone-sensitive cancers in particular.
The seed contains the cyanogenic glucoside linamarin, which in the presence of the endogenous enzyme linase (released after seed crushing) hydrolyses to form the poisonous hydrogen cyanide. Prior heating of the presscake avoids cyanide intoxication. The protein in the seedcake is low in lysine. Linseed cake and meal are said to have a regulatory effect on the digestive system of livestock, to increase the butterfat yield in dairy cows and to promote a shiny sheen in the coats of show animals.
Embedded within the cortex of the stem is a ring of 20–50 fibre bundles. Each of these bundles represents a single strand of commercial fibre. The proportion of fibre in the whole dry stem is influenced by both genotype and growing conditions and ranges from 28–36%. Each fibre bundle is made up of 10–40 fibre cells that are longitudinally interlocked and cemented to each other by pectins. The fibre cells are (1–)10–40(–100) mm long with a diameter of (5–)10–30(–40) μm and a narrow lumen. They are tapered at either end, round to polygonal in cross-section. The fibre cells of linseed genotypes tend to be shorter and coarser with a smaller lumen. The chemical properties of the fibre are: cellulose 60–85%, hemicellulose 9–19%. lignin 2–15% and pectin 0–9%. Flax fibre has a high moisture absorbency and is stronger than the fibre of cotton, rayon and wool, but weaker than ramie fibre. It is soft, lustrous and flexible, but not as flexible or elastic as cotton and wool fibres. The tensile strength, elongation at break, and Young’s modulus of flax fibre are 345–1035 N/mm², 1.3–3.3% and 27,000–80,000 N/mm², respectively. The fibre cells in the xylem surrounding the pith and hollow central cavity of the plant have a mean length of 0.5 mm and a mean diameter of 16 μm.
Adulterations and substitutes
Vegetable oils for human consumption can often be interchanged, blended or transesterified. In Ethiopia some linseed oil is blended with other high quality oils such as oil of niger seed, sunflower or safflower. Blending is done to minimize the formation of rancidity and so maintain an acceptable flavour. Safflower is also used instead of linseed to prepare a local dish called ‘fit-fit’ (a mixture of linseed flour, water and spices with local bread), which is often served during fasting seasons.
Erect annual herb up to 120 cm tall; root system consisting of a taproot with subsequent branching to a depth of up to 60 cm; stem slender, erect, glabrous, greyish green, often slenderly branched in the upper part. Leaves alternate to almost opposite in lower part of stem, alternate in upper part, simple and entire, sessile, without stipules; blade narrowly elliptical to linear or lanceolate, up to 50 mm × 5(–8) mm, glabrous, dull medium green, 3-veined from base to apex. Inflorescence a loose, terminal, leafy corymb. Flowers bisexual, regular, 5-merous; pedicel erect, 1–3.5 cm long; sepals free, broadly elliptical-ovate, 5–10 mm × 2–5 mm, acuminate; petals free, obovate, 8–15 mm × 4–11 mm, shortly clawed at base, margin slightly toothed, white to pale blue or purple-blue with hues of pink; stamens 5, united at base in a glandular ring, free part 2–6 mm long; styles 5, often shortly connate at base, 2–3 mm long, stigmas linear club-shaped, 1–2 mm long. Fruit a globose capsule 7–10 mm in diameter, 5-celled but often each cell divided by a secondary septum, up to 10-seeded. Seeds compressed, 6–10 mm × 2–3 mm, with indistinct, c. 1 mm long beak, glossy yellow to dark brown. Seedling with epigeal germination; hypocotyl 1.5–4 mm long, epicotyl up to 1.5 mm long; cotyledons elliptical-oblong, 6.5–14 mm long, leafy.
Other botanical information
Linum comprises about 200 species. Linum usitatissimum is the only important crop, although a few species have ornamental value. Linum usitatissimum is highly variable and to classify this variability numerous subspecific groupings have been proposed. Two main groups are obvious: cultivars grown for the seed and those grown for the fibre. There is also a group of cultivars that are grown for both their seed and fibre. In all 3 groups numerous cultivars exist.
Changes in the nuclear DNA of certain flax cultivars can occur within a single generation due to specific environmental conditions. The characteristics altered include plant height, weight, number of branches and total nuclear DNA. These changes are not random events, but have been shown to occur repeatedly and to be inherited in the progeny.
Linum emirnense Bojer, a perennial herb up to 30 cm tall and Linum betsiliense Baker, a shrub up to 2 m tall, both endemic to Madagascar, also have fibrous stems. The former is used for making cushions to carry water vessels on the head, the latter can be used for weaving.
Growth and development
Under tropical conditions, seeds germinate and emerge within 7–10 days after sowing. The first true leaves appear within 2–3 days after emergence. Early growth is slow under cool conditions. The taproot reaches 15 cm when the stem is 3–4 cm long. The taproot, and under dry soil conditions also lateral roots, of some cultivars may grow to a depth of 1 m. Branching is a cultivar characteristic; in some cultivars, e.g. from Ethiopia, branches are formed in the axils of the cotyledons or lower leaves; many linseed cultivars branch strongly from higher nodes, while fibre flax forms very few branches.
Fibre flax is a quantitative long-day plant, linseed is less photoperiod sensitive. Flowers open shortly after dawn and are predominantly self-pollinating. Pollination occurs round mid-morning. Some cross-pollination may occur depending on the population of insects, such as bees. The petals drop after pollination, with complete loss around midday. Stem length reaches its peak soon after flowering. Flowering is indeterminate, resulting in uneven formation of the capsules and subsequent maturation. As the capsules mature, they turn brown as the lower leaves and stem turn yellow. Seeds in the capsules become pale brown, plump and pliable, indicating maximum dry matter content. Seed ripeness is reached when the seeds are free and can be heard rattling inside the capsule.
Linseed cultivars produce about 60 leaves per plant, fibre flax cultivars about 80. Number of capsules per plant varies with genotype, management and climatic conditions but will typically range from 5–15 per plant. Total crop duration of linseed is normally 100–180 days, with 40–60 days from first flowering to harvest. For fibre flax the duration from sowing to harvesting is 90–120 days, to seed maturity 140–200 days.
Good seed yield can be achieved with a temperature range of 10–30°C, a midday relative humidity of 60–70%, and rainfall of 150–200 mm distributed over the 3-month growing period. Temperatures of –6°C may kill the crop in the seedling stage and frost may also cause injuries during the flowering and green capsule stages. Warm and dry conditions from early capsule development to maturity are required for curing the seed and for threshing. Rainfall towards maturity of the crop may cause secondary flowering and hence uneven maturity. Heavy rain and strong winds may cause lodging. In Ethiopia reasonable seed yields are obtained at 1600–2800 m altitude. In fibre flax hot dry days prior to and during flowering tend to cause branching resulting in shorter, more woody stems.
Optimum soils for flax are well drained but moisture retentive and medium to heavy textured, such as clay loams and silty clays. The soil should be of a fine tilth and not prone to crusting. Flax will not perform well on soils with pH less than 5 or above 7 and is sensitive to soil salinity.
Propagation and planting
Flax is propagated by seed. The weight of 1000 seeds ranges from 4–13 g. Owing to the small seeds and poor competitiveness of the seedlings with weeds, a finely prepared, weed-free seedbed with adequate moisture is essential for successful crop establishment. Ploughing and harrowing or two or three passes with a traditional plough can do this. The seed may be broadcast by hand and then covered by dragging twigs of trees across the field. It can also be disked or harrowed but this may result in uneven sowing depth, emergence and maturation. Thus, sowing with a seed drill is preferred. The optimum sowing depth depends on soil type and moisture level. In heavy soils, 1.5 cm is usually enough, while on lighter soils, a depth of 2 cm reduces the risk of drought. On soils in which crusting occurs after heavy rain, making emergence difficult, a light harrowing is advisable. The seed rate depends on genotype, planting method, moisture conditions and objective of production. Higher seed rates are recommended for hand-sown crops and under high moisture conditions. Recommendations for linseed range from 17 kg/ha under low-rainfall conditions to 55–90 kg/ha under optimum water supply. Seed rates of 25 kg/ha are optimum for row-planted linseed in Ethiopia, with row spacing of 20 cm and a plant density of about 500 plants/m²; for broadcasting seed rates of 35–40 kg/ha are recommended. For fibre flax a seed rate of 80–110 kg is recommended for optimum conditions when a seed drill is used; up to 150 kg/ha is recommended for hand-sown crops. Row spacings for fibre flax are 6–15 cm with a plant density of 1800–3300 plants/m². Seeds for planting should be free from weed seeds, shrivelled or diseased seeds and preferably treated with a fungicide.
Young linseed plants do not compete well with weeds and good weed control is necessary. This can be achieved by hand weeding twice (3 and 5 weeks after sowing) or with a range of pre- or post-emergence herbicides. Usually, early ploughing is practised to stimulate the germination of weed seeds, followed by shallow harrowing prior to sowing to kill the weeds. Water stress during flowering and early seed development negatively affects seed yield and quality, and where possible supplementary irrigation is recommended from budding until late grain filling. Later irrigation may lead to secondary flowering and uneven ripening. Linseed and fibre flax require relatively small amounts of nutrients though their uptake depends on soil type, cultivar and weather conditions. Typical uptake rates for a linseed or fibre flax crop yielding 5–6 t straw and 0.6–0.8 t seed per ha are approximately 50–75 kg N, 10–16 kg P, 40–60 kg K, 18–36 kg Ca and 8–11 kg Mg. In Ethiopia recommended rates of fertilizer for linseed are 23 kg N and 10 kg P per ha; average recommendations in the United States are 50 kg N, 25 kg P and 50 kg K per ha.
In fibre flax high N rates promote lodging, branching, lignification of the fibre and reduction of fibre wall thickness. Therefore, fibre flax never receives high rates of inorganic nitrogen and responds well to split applications. Ideally, the crop should draw most of its nitrogen from soil organic matter. Ample P is required for good seed yields and high-quality fibre, but excessive rates can result in reduced fibre quality. Sufficient K is essential for both fibre yield and seed quality. Organic manures are best applied to the preceding crop, as direct organic manuring may promote lodging and cause uneven growth.
Crop rotation is required for reducing weed infestation, disease development and improving organic matter of the soil. Flax should preferably not be grown in the same field more than once every 5–6 years and is best grown in a rotation that reduces weed infestation. It performs well after pulses, cereals and potatoes.
Diseases and pests
The main diseases affecting linseed and fibre flax are caused by soil- or seed-borne fungi and can usually be controlled by seed dressing, rotation or use of disease resistant cultivars. The major seed-borne diseases are anthracnose (Colletotrichum linicola), grey mould (Botrytis cinerea), pasmo (Septoria linicola, anamorph Mycosphaerella linicola) and blight (Alternaria spp.). The symptoms of these diseases are stem or leaf lesions. Browning and stem break is a complex of symptoms caused by seed-borne Polyspora lini (synonym: Aureobasidium lini, teleomorph Discosphaerina fulvida). Early infection causes stems to break, infection at a later stage causes elongated brown lesions with purplish margins on the upper parts of the stem, giving heavily affected patches a brown appearance. The principal soil-borne diseases include stem rot (Sclerotinia sclerotiorum), wilt (Fusarium oxysporum) and scorch (Pythium megalacanthum). These diseases attack the root system or the lower part of the stem resulting in either lodging or the cessation of growth and gradual death of the plant from the top downwards. Another disease, rust (Melampsora lini), is characterized by the occurrence of bright red pustules (uredospores) on above-ground plant parts, later on replaced by black encrustations (teliospores). The spores are carried with the seed and on chaff fragments and can survive in the soil for up to two years. In infected areas, rust resistant cultivars should be used. It can also be controlled through seed dressing and crop rotation of 3–4 years. Powdery mildew (Odium spp.) is another fungal disease and its control is similar to rust. A recent survey showed that wilt, pasmo and powdery mildew are most prevalent in Ethiopia.
Linseed and flax attract a wide range of pests, but most are not considered to be of economic importance. Some may cause severe damage, however, if left unchecked: cutworms (Agrotis sp.) gnaw through young stems at ground level; red-legged earth mites (Halotydeus destructor) suck the sap from young seedlings resulting in low vigour and possible seedling death; various aphids cause damage through direct feeding or disease transmissions; sap-sucking thrips may retard growth and kill the plant; especially in Europe the larvae of flea beetles (Aphthona euphorbiae and Longitarsus parvulus) damage roots while the adults feed on leaves, stem and seed; in Canada potato aphid (Macrosiphum euphorbiae) became a pest of flax in the 1990s, while the caterpillars of Heliothis spp. penetrate the young capsules and cause substantial damage in Australian crops. Control is achieved either through the use of insecticides or by sowing the crop at a time of the year that is out of synchronization with the pest’s life cycle.
Various birds may feed on young plants and remove the growing point, resulting in tillering and subsequent non-uniformity of maturation and a decline in yield. Bird control measures such as scarecrows, humming lines and gas guns, and a rapid establishment of the crop are recommended.
The optimum time for harvesting linseed is when most capsules are fully mature and turn brown. At this stage, the seeds make a rattling sound in their capsule, while the stem and leaves turn yellow. The moisture content of the seeds will decrease to 10–15%. In Ethiopia harvesting is largely done manually by cutting the stems with a sickle. Some farmers harvest linseed by pulling the stems out of the ground to use them for making utensils, such as sweepers, baskets, etc. Threshing is done manually by beating the capsules with sticks or by oxen or horses trampling them on a well-prepared threshing floor. Then the seeds are separated from chaff by winnowing. In North America short-straw linseed is combine harvested when the seed is sufficiently dry (<10% moisture); under more humid conditions it is cut and swathed to dry before threshing.
The optimum time for harvesting fibre flax is when the leafy stems are green-yellow and the capsules are still forming, at which time the fibres are long and supple. Flax harvested too early and still green produces fine and weak fibres. Conversely, over-ripe, brown to dark brown flax yields brittle fibre with a high proportion of tow. Flax is typically pulled out of the ground rather than cut, to preserve the full length of the fibres. This is done by hand or with pulling machines, which pull and lay the crop on the ground in swathes. The capsules can be removed during pulling or left on the plant during retting and baling and removed in the processing factory. Threshing of the seed is usually done concurrently with ‘scutching’ of the fibre. Industrial flax or dual purpose crops are often combine harvested with conventional combine harvesters to avoid the cost of specialized pulling and turning equipment.
World average seed yields of linseed in the period 2004–2008 were nearly 0.9 t/ha per year. In cool-temperate regions up to 2.0 t/ha is attainable with cultivars of 140–160 days duration. The yield potential of modern cultivars of linseed is estimated at about 3.0 t/ha. The average seed yield in Ethiopia is 0.7 t/ha, while improved cultivars with good management yielded up to 2.5 t/ha in favourable areas, such as Bekoji in the south-eastern part of the country. In Kenya yields of up to 2.3 t/ha have been achieved in experimental fields.
Average world flax (fibre and tow) yields have increased to about 1.5 t/ha per year; the highest yields being reported from Czech Republic (3.3 t/ha) and China (2.9 t/ha). In experiments in Australia stem yields of up to 8.8 t/ha, fibre yields of 1.3–2.6 t/ha and seed yields of 1.6–2.2 t/ha have been obtained.
Handling after harvest
Threshing of linseed can be done about a fortnight after harvesting if dry and windy weather situations prevail; if not linseed plants are sun dried for up to 30 days. Seeds can be stored for a long period of time in clean containers under dry and well-aerated conditions. Optimum seed moisture for long-term storage is 9% or less. So far, no storage pests have been reported for linseed in Ethiopia. Traditional methods of oil extraction involve boiling of pounded and macerated seed in water and skimming off the floating oil. Small-scale oil extraction in rural areas has been made more efficient with the introduction of inexpensive screw presses, similar in design to the horizontal expellers of large oil mills, operated by hand or powered by a small diesel engine or electricity.
For fibre production retting is most commonly done in the field in a process called ‘dew retting’. The duration and uniformity of dew retting depend on weather conditions. Ideally, harvesting needs to be followed by alternating periods of rain and dry weather; there must be sufficient moisture to ret the straw, but continuous rain can lead to over-retting and loss of fibre quality. To improve the uniformity of dew retting, it is necessary to turn the crop 3–4 times to expose the underside of the crop. When retting is complete and the crop is dry, it can be baled and stored. A range of off-field retting methods exist which are faster and provide greater uniformity of separation, but they are generally more expensive. Dried and retted stem material is ‘broken’, which involves rolling and/or crimping the stem to loosen the core from the bark. The core is then removed via a process known as ‘scutching’. The separated bast fibre is ‘hackled’ by passing it through a series of combs of increasing fineness that scrape and buff the fibre. The end products are ‘line flax’, ready to be spun into yarn and ‘tow’ used in the manufacture of paper and other industrial applications.
Linum usitatissimum has been cultivated in many parts of the world and is very variable. Three distinct centres of diversity are recognized: the Mediterranean and western Asia, India and Ethiopia. Large germplasm collections are maintained in the main production countries: Biodiversity Conservation and Research Institute, Addis Ababa, Ethiopia (3110 accessions); Institute of Crop Germplasm Research (CAAS), Beijing, China (2556 accessions); Institute of Food and Oil Crops, Shijiazhuang, China (2165 accessions); Suceava Genebank, Suceava, Romania (4910 accessions) and the North Central Plant Introduction Station, Ames (IA), United States (2815 accessions). Important collections are also maintained in other countries in Europe. Preliminary collection and characterization of linseed has been underway in Ethiopia at Holetta Research Center since the early 1980s in collaboration with the Biodiversity Conservation and Research Institute. A recent analysis of the genetic diversity of 60 Ethiopian and exotic accessions, using morphological and molecular methods, revealed the presence of tremendous genetic diversity.
Breeding methods are those applied to self-pollinating crop species. Most linseed and flax cultivars grown today are pure lines developed by pedigree selection after crossing (and backcrossing) genotypes with contrasting characteristics. Breeding objectives for linseed focus primarily on seed yield and oil content. Breeding for seed quality is aimed largely at the fatty acid composition and has led to the development of low-linolenic acid cultivars in Australia and Canada. In cultivars developed for non-food purposes on the other hand, the linolenic acid content needs to be high. Breeding for disease resistance has resulted in cultivars that are resistant to Fusarium wilt and to rust. Breeding work in Ethiopia has concentrated on the development of disease resistance and all released cultivars are relatively resistant to wilt.
Well-known linseed cultivars include: ‘AC-Emerson’ and ‘McDuff’ (Canada), ‘Verne 93’ (United States) and the ‘Solin’ (low linolenic acid) cultivars ‘CDC gold’ and ‘2047’.
Some of the cultivars grown in Ethiopia are (with year of release): ‘CI-1525’ and ‘CI-1652’ (1984): medium to late maturing, good seed yield, high oil content, brown seed, blue flowers, tolerant to wilt, pasmo and powdery mildew; ‘Chilalo’ (1992): medium to early maturing, high yielding, medium oil content, brown seed, tolerant to wilt, pasmo and powdery mildew; ‘Belay-96’ (1996): similar to ‘Chilalo’ but with higher yield and oil content; ‘Berene’ (2001): similar to ‘Chilalo’ but adapted from mid to higher altitudes and with higher oil content; ‘Tolle’ (2004): medium maturing, high yielding, medium oil content, pale-brown seed, tolerant to wilt, pasmo and powdery mildew.
In fibre flax, breeders emphasize fibre content or fibre wealth (the ratio of fibre weight to total stem dry weight) more than fibre yield, as the latter is strongly influenced by management and environmental factors. Fibre quality is particularly important for flax grown for textile fibre. Important selection criteria for fibre quality are homogeneity, degree of lignification, strength, fineness and water uptake. Selection for industrial fibre flax may emphasize productivity rather than quality traits, given the normally negative correlation between these two traits. Substantial breeding efforts have been made to improve lodging resistance via straw stiffness and fibre content. Important fibre cultivars are: ‘Ariane’, ‘Viking’ and ‘Viola’ (France), ‘Svetoch’, ‘Alexim’ and ‘Lenok’ (Russia) and ‘Heiya’, a family of cultivars being developed in north-eastern China.
Various plant biotechnological techniques are finding useful application to supplement conventional linseed and flax breeding, such as in-vitro culture (explants, protoplasts, anthers, microspores), molecular marker-assisted selection, genomics and genetic transformation.
After a long period of stagnation of flax and linseed production, mainly due to the dominance of petroleum-based synthetic fibres and drying agents, the demand for the products of this crop has been growing rapidly in recent years due to a trend towards eco-friendly and natural raw materials. Linseed is also emerging as a major nutraceutical crop with a wide range of biologically active constituents present in the seed that promote health and may help prevent some important chronic diseases. World production of linseed and flax is expected to expand in the near future in response to increasing demands. Suitable conditions for profitable linseed production do exist in the highlands of East Africa.
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Sources of illustration
- Seegeler, C.J.P., 1983. Oil plants in Ethiopia, their taxonomy and agricultural significance. Agricultural Research Reports 921. Pudoc, Wageningen, Netherlands. 368 pp.
- W. Adugna, Ethiopian Institute of Agricultural Research, Holetta Research Center, P.O. Box 2003, Addis Ababa, Ethiopia
Correct citation of this article
Adugna, W., 2011. Linum usitatissimum L. [Internet] Record from PROTA4U. Brink, M. & Achigan-Dako, E.G. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 3 March 2020.
- See the Prota4U database.