Linum usitatissimum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Linum usitatissimum L.

Protologue: Sp. pl.: 277 (1753).

Family: Linaceae

Chromosome number: 2n= 30, 32

Vernacular names

• Flax, textile flax (when grown for fibre), linseed (when grown for seed) (En). Lin (Fr)
• Indonesia: linum
• Thailand: linin (central), huu-mua (central)
• Vietnam: cây lanh.

Origin and geographic distribution

The primary centre of origin of L. usitatissimum has not been established beyond doubt. The large diversity of forms around India suggests that it may have originated there and been spread northwards and westwards by early domesticators. The Mediterranean has also been suggested as a possible centre of origin. The distribution and domestication of L. usitatissimum on a global basis occurred principally as a fibre crop. Flax provided the fibres needed for cloth and cordage, and linen was used by the Egyptians, Greeks and Romans. The crop has been cultivated for thousands of years; it was commercially traded by the Egyptians by 4000 B.C. and remnant seed has been found in prehistoric settlements in the Swiss Alps. The high oil content of the seed was also appreciated and a degree of specialization occurred: Mediterranean and European types developed into the principal flax forms, and short-season variants adapted to the warmer climates of West and South Asia developed into linseed types.

L. usitatissimum is now grown widely in many parts of the world, including the tropics. Flax is typically grown in cool, temperate regions including Russia, Northern Ireland, Belgium and other northern and eastern European countries. Linseed prefers warmer climates and is cultivated in parts of South America, the United States, Canada, Africa, India, Bangladesh and Australia. In South-East Asia L. usitatissimum is cultivated in northern Thailand (Chiang Mai) and locally on a small scale in Indonesia (Java). After successful experimentation with flax in the mountains of Java in the first half of the 20th Century, interest in flax cultivation in Indonesia was revived in the 1970s and 1980s with the objective of reducing flax fibre imports for paper making.

Uses

Linen is the most important product made of the bark fibre of flax and is used variously for household textiles (towels, table cloths etc.), furnishings (curtains, wall coverings and upholstery fabrics) and clothing. The properties making it ideally suited for these applications are high moisture absorption, strength, launderability, excellent colour fastness and resistance to shrinkage. A disadvantage is that it creases easily.

The bark fibre is also used in the manufacture of fine papers such as cigarette, art, currency, archival and security papers, often in blends with other wood and non-wood pulps. The fibre used for paper typically comes from one of three sources:

• waste material from spinning and weaving mills and linen rags, representing the purest form of flax fibre, free of core material and used for the highest paper grades;

• short bark fibre or waste product left over from the processing of the high quality textile fibre ("flax tow");

• mechanically decorticated straw of flax that has been grown primarily for seed ("seed flax tow"), which is the least pure form of fibre, producing pulps that are usually weaker and less durable than flax tow pulps.

Straw from seed flax is also utilized in the manufacture of twine, bagging and insulating wallboards. The waste woody core resulting from bark fibre extraction is used in the manufacture of chipboard or, in combination with bark fibre, for paper making.

Linseed oil contains linolenic acid, which makes it ideally suited as a drying agent in protective coatings such as paint, stains and varnish or by itself as a raw or boiled oil. Linseed oil is also used in the manufacture of window putty, soaps, printing ink, erasers and linoleum, and as waterproofing for raincoats and tarpaulins. A number of edible "Linola" lines have been bred with reduced linolenic acid content and high levels of linoleic acid, valued for human consumption. Linola oil is used in the manufacture of margarine and cooking oil. Other cultivars have been bred for mucilage production from the seed. This mucilage, formed on the outside of the seed when large epidermal mucilaginous cells swell upon exposure to water, is used in treating a range of digestive complaints. Linseed cake and meal are the by-products of oil extraction and are used as protein supplements in livestock rations after prior removal of anti-nutritional and toxic substances.

Production and international trade

According to FAO estimates the average annual world flax (fibre and tow) production in 1996-2000 was about 500 000 t from an area of about 490 000 ha. The main producers in this period were China (181 000 t/year), France (67 000 t/year), Spain (58 000 t/year), the Russian Federation (38 000 t/year) and Belarus (34 000 t/year). The average annual flax (fibre and tow) exports amounted to 124 000 t, with a value of US$ 228 million. The principal exporters were France (54 000 t/year) and Belgium (45 000 t/year), the main importing countries Belgium (27 000 t/year), China (25 000 t/year) and Italy (15 000 t/year). In the 1980s Indonesia imported about 15 000 t of flax fibre per year for the production of high-quality paper, but in 1996-2000 the average annual imports were only 70 t.

The estimated average annual world linseed production in 1996-2000 was about 2.5 million t from 3.1 million ha, with the main producing countries being Canada (0.9 million t/year), China (0.4 million t/year), India (0.3 million t/year) and Germany (0.2 million t/year).

Properties

Embedded within the stem cortex of L. usitatissimum are approximately 30 groups of flexible fibre bundles. Each of these bundles (referred to as "bast") represents a single strand of commercial fibre. The proportion of bast 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. The fibre cells are (1-)10-40(-85) mm long with a diameter of (5-)10-30(-38) μm and a narrow lumen. They are tapered at either end, round to polygonal in cross-section and interlock longitudinally to form the bundles. The fibre cells of the linseed genotypes tend to be shorter and coarser with a smaller lumen. The chemical properties of unretted and retted raw material are, respectively: cellulose 56.6% and 64.1%, hemicelluloses 15.4% and 16.7%, pectin 3.8% and 1.8%. Unretted material contains 2% lignin. Flax fibre has a high moisture absorbency and is stronger than that 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. Typical values of the tensile strength, elongation at break, and Young's modulus of flax fibre are 345-1035 N/mm², 2.7-3.2% and 27.6 GPa, 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.

Per 100 g the seed contains 35-44 g oil and about 20 g protein. The approximate fatty acid composition of linseed oil is: linolenic acid 30-60%, linoleic acid 10-25%, oleic acid 13-36% and stearic and palmitic acids 6-16%. In the breeding of edible Linola lines, linolenic acid levels were dramatically reduced to about 2%, with an accompanying increase in the level of linoleic acid. The proportion of the other fatty acids remained relatively stable. The seed or cake contains the cyanogenic glucoside linamarin which, in the presence of the enzyme linase, hydrolyses to form poisonous hydrogen cyanide. To counter this problem, the feed should be boiled in hot water prior to consumption. Linseed cake and meal are said to have a regulative effect on the digestive system, to increase the butterfat yield in dairy cows and promote a healthy sheen in the coats of show livestock.

The weight of 1000 seeds is 3-12 g.

Adulterations and substitutes

Because of its similar physical and chemical fibre properties, hemp ( Cannabis sativa L.) is often used in place of or in a blend with flax fibre in paper and textile manufacture.

Description

An erect annual herb, up to 1.2 m tall. Root system consisting of a taproot with subsequent branching to a depth of up to 60 cm. Stem slender, erect, usually solitary, up to 120 cm × 4 mm (shorter in seed cultivars), glabrous, greyish-green, slenderly branched in the upper 12-24 cm (more richly branched in seed cultivars). Leaves subopposite to spirally arranged, sessile, simple; blade narrowly elliptic, linear or linear-lanceolate, (10-)25-35(-50) mm × (2-)3-5 mm, 3-veined, glabrous, greyish-green. Inflorescence a loose, terminal, leafy corymb, with flowers leaf-opposed; pedicel erect, 1-3.5 cm long; flowers bisexual, 2-3 cm in diameter, 5-merous; sepals free, broadly elliptic-ovate, 5-10 mm × 2-5 mm, entire, acuminate; petals free, obovate, 8-15 mm × 4-11 mm, shortly clawed at base, margin dentate-crenate, white to pale or purple-blue with hues of pink; stamens 5, united at base in a glandular ring, alternating with the petals, free part about 2-6 mm long; styles 5, often shortly connate at base, about 2-3 mm long, each one ending into a linear-clavate stigma 1-2 mm long. Fruit a globose capsule, 7-10 mm in diameter, 5-carpellate and 5-loculed but often each one divided by a secondary septum, each locule with 2 seeds, up to 10 seeds per fruit. Seed compressed, (4-)6-10 mm × 2-3 mm, yellow to dark brown, beak about 1 mm long; testa with a shiny, slippery appearance.

Growth and development

In warm and moist conditions, flax seeds germinate and emerge within 7-10 days after sowing. True leaves appear within 2-3 days of emergence, when the stalk is about 3-4 cm long and the tap root about 15 cm. The first pair of true leaves are almost opposite, after which phyllotaxis changes to spirally alternate. While there is normally a single stem, tillering is stimulated by difficult emergence, low plant population or damage due to pests, frost or chemicals. Initial growth can be slow if early growing conditions are cool. Flowers open shortly after dawn with predominantly self-pollination occurring by mid-morning. Some cross-pollination is possible through bees. The petals fall shortly thereafter, with complete loss by about noon. The plant reaches its maximum height towards the end of flowering. At this time the crop is particularly susceptible to lodging. Flowering is indeterminate, resulting in uneven formation of the capsules and subsequent maturation. As the capsules mature, they begin to turn brown at the same time as the lower leaves and stem turn yellow. Eventually the leaves senesce and drop. Seed in the capsules becomes light brown, plump and pliable, indicative of maximum dry matter content. Seed ripeness is reached when the seeds are free and can be heard to rattle within the capsule. Flax genotypes typically produce about 80 leaves per plant and seed genotypes about 60. Fruit number per plant varies with genotype, management and climatic conditions but will typically range from 5-15 per plant. Total crop duration of fibre flax is normally 90-120 days, with 30-45 days from first flowering to harvest. The duration from sowing to seed maturity is 140-200 days.

Other botanical information

Linum L. contains about 200 species, mainly in the Mediterranean region, but only L. usitatissimum is an important fibre crop. L. usitatissimum is only known from cultivation. It is thought to have been derived from L. bienne Miller (synonym L. angustifolium Hudson), a wild biennial or perennial species from western and southern Europe (same chromosome number, crossing is easy and hybrids are fertile).

L. usitatissimum is a highly variable crop and to classify this variability numerous subclassifications have been made, making its taxonomy confusing. In a cultivated crop it is more appropriate to distinguish only cultivar groups and cultivars, and to refrain from subclassifications primarily developed for wild species. Unfortunately, a generally accepted cultivar classification for flax does not exist yet. Two main groups are obvious: cultivars grown for the stem fibres and those grown for the seed. In both groups numerous cultivars exist. For the seed a distinction can be made between cultivars grown for the oil of the seed (linseed) and others for the high mucilage potential of the seed coat. There is also a small group of cultivars that are grown both for the fibre and the seed.

Some well-known fibre flax cultivars are:

• "Ariane" (France): medium to early maturing; seed yield low; flowers blue; resistant to lodging.

• "Viking" (France): maturing like "Ariane", but with higher fibre and seed yield; resistant to lodging; excellent resistance to rust, moderate resistance to wilt, susceptible to pasmo.

• "Belinka" (the Netherlands): medium maturation; higher straw and fibre yield than "Ariane"; good seed yield; flowers white; susceptible to lodging.

• "Marina" (France): cross between "Belinka" and "Natasja"; medium to early maturing; good fibre and seed yields; susceptible to lodging.

• "Regina" (the Netherlands): medium to early maturing; susceptible to lodging.

Other fibre flax cultivars are "Arc" and "Ciel" (developed in Belgium); "Fany" (France); "Wiera" (the Netherlands); various Liral, Stormont and Norfolk cultivars (United Kingdom); "Minerva" (Poland); "Milenium" (Roumania, Hungary); "Progress" (Russia); "Giza 2 and 4" (Egypt); "Tainung No 1 and No 2", "Taichung Special No 1" (Taiwan); "Banner", "Flag" and "Standard" (Australia); and "Cascade" (United States).

Some well known linseed cultivars are:

• "Dufferin" (Canada): very late maturation; yield high when sown early, but not recommended for late sowing; plant height variable, flowers blue, seed brown; oil content high; resistant to rust and wilt.

• "Rahab" (United States): medium maturation; yield high; oil content high; flowers blue, seed brown; good resistance to lodging; resistant to rust, moderately susceptible to wilt and pasmo.

• "Verne" (United States): early maturation; yield high, particularly when sown late; good resistance to lodging; flowers blue, seed brown; with excellent resistance to rust and wilt, and moderate resistance to pasmo.

• "Antares" (France): medium to early maturation; plant height medium; yield-potential high; susceptible to Botrytis and rust.

• "Atalante" (France): later maturing and taller than "Antares", but with similar yields; less resistant to lodging than "Antares", but more resistant to rust.

Ecology

L. usitatissimum is a long-day plant. The crop requires moderate to cool temperatures and adequate moisture during the growing season to achieve optimum fibre yield and quality. Optimum results in Europe are achieved with a temperature range of 10-30°C, a midday relative humidity of 60-70%, and a rainfall of 150-200 mm distributed over the typical 3-month growing period. Hot dry days prior to and during flowering tend to cause branching and hasten flowering, resulting in shorter, more woody stems, lower fibre yield and harsh, dry fibres. Heavy rains and strong winds may cause lodging. Temperatures of -6°C may kill the crop in the seedling stage and frost may also cause injury during the flowering and green capsule stage. Warm, dry conditions from early capsule development to maturity are particularly beneficial for curing the seed as well as for threshing and for drying the straw after retting. Rainfall during this time may cause secondary flowering and hence uneven maturity. Where dew retting is performed, there must be sufficient moisture during the post-harvest period to ret the straw. Experiments in Java in the 1930s indicated that reasonable yields of good quality fibre can be obtained at 1000-1600 m altitude. In experiments in the early 1980s at altitudes from 800 to 1400 m, the 13 cultivars involved grew best, in terms of plant height and straw dry weight, at 1200 m altitude.

Optimal 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 capping or crusting. Flax is particularly sensitive to saline soils and will not perform well on soils with pH less than 5 or above 7.

Propagation and planting

Flax is propagated by seed. Because of the small seed size and poor competitive ability of flax seedlings, a finely prepared, weed-free seed bed with adequate moisture is essential for successful crop establishment. The seed may be broadcast by hand and then covered by discing or harrowing, but this method results in uneven sowing depth, emergence and maturation. Therefore, sowing with a grain drill is preferred. The optimal sowing depth depends on soil type and moisture level. In heavy soils, 1.5 cm is usually enough, whereas on lighter soils, a depth of 2 cm ensures imbibition. The seed rate depends on genotype, planting method, expected moisture conditions during the season and production objective (fibre, seed or both). With a drill, seed rates for fibre crops under optimal water supply are 80-110 kg/ha. Higher rates (up to 150 kg/ha) are recommended for hand-sown crops. Seed rate recommendations for linseed are variable, ranging from 17 kg/ha under low-rainfall conditions to 55-90 kg/ha under wetter conditions. Row spacing for fibre flax ranges from 6-15 cm, with a plant density of 1800-3300 plants/m². On some soils, crusting will occur after heavy rain, making emergence difficult. A light harrowing is advisable for breaking the crust. Seed for planting should be freed from all light, shrivelled, scaly or diseased stock and treated with a fungicide to kill surface-borne diseases.

An experiment in the 1980s in Manoko Experimental Garden (near Bandung in Java, at 1200 m altitude) with 12 flax cultivars showed that stem yields were higher when seeds were sown in November or January than when sown in March. In another experiment at the same location, with 12 plant spacings, the highest straw yields were obtained at densities of 2.5 cm within the row and 10 or 15 cm between rows.

Husbandry

Flax is a small plant and is not very competitive, so good weed control is important and can be achieved through a range of pre- and post-emergent herbicides. Early working of the soil to stimulate weed seed germination, followed by shallow preparation prior to planting may help to obtain a clean seedbed. Weed control is not only vital for maximizing fibre and seed yields, but also for avoiding impurities when processed.

Seed quality and yield are adversely affected by water stress during flowering and early seed development. In areas where rainfall is likely to be limiting during this period, irrigation is suggested from budding until late grain filling. Later watering may cause secondary flowering and uneven ripening. The best results are obtained with light irrigations, owing to the shallow-rooted nature of the crop.

Flax requires relatively small amounts of nutrients and excessive fertilization can result in a serious decrease of fibre quality. Hence, fertilizer rates should be such as to achieve a balance between maximizing yield without adversely affecting quality. Nutrient uptake depends on a range of factors including soil type, cultivar and weather conditions. Typical uptake figures for a fibre flax crop yielding 5-6 t straw and 0.6-0.8 t seed per ha are: 50–75 kg N, 10-16 kg P, 40-60 kg K, 18-36 kg Ca and 8-11 kg Mg. The actual quantities removed at harvest are somewhat less, owing principally to leaf detachment. High nitrogen rates promote lodging and have an adverse effect on fibre quality through promotion of branching, lignification of the fibre and reduction of fibre wall thickness. Therefore, flax never receives high rates of inorganic nitrogen and responds better to split applications. Ideally, the crop should draw most of its nitrogen from soil organic matter. Ample phosphorous is required for good seed yields and high-quality fibre, but excessive rates can result in reduced fibre quality. Sufficient potassium is essential for both fibre yield and quality. Adequate potassium nutrition promotes fibre strength, flexibility, elasticity, and suitability for spinning. It also tends to prevent lodging and disease damage through the promotion of longer and thicker stems. Recommended rates of application for mineral fertilizers vary widely, depending on yield level, soil type and seed rate. Organic manures should ideally be applied to the preceding crop, as direct organic manuring may promote lodging and cause uneven growth.

Flax should preferably not be grown in the same field more than once every 5-6 years and is best grown in a rotation which reduces weed infestation and disease development, ensures adequate soil organic matter and enables the preparation of a fine seedbed. It does well after beans, maize, potatoes and peas, but weed-free land previously sown to lucerne, wheat or barley is also suitable.

Diseases and pests

The majority of diseases afflicting L. usitatissimum are caused by soil- or seed-borne fungi and can usually be controlled by thorough seed disinfection, rotation or the use of disease resistant cultivars. The principal seed-borne diseases are anthracnose ( Colletotrichum lini ), stem break and browning ( Polyspora lini ), grey mould ( Botrytis cinerea ) and pasmo ( Mycosphaerella linorum ). Typical symptoms of these diseases are stem or leaf lesions usually appearing early in the life of the plant. Key soil-borne diseases include sclerotinia ( Sclerotinia sclerotiorum ), wilt ( Fusarium lini ), foot rot ( Phoma sp.) 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 crown downward. Another disease, rust ( Melampsora lini ) is characterized by the occurrence of bright red pustules (containing uredospores) on aboveground plant parts, later in the season 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; if susceptible cultivars are grown, infection can be controlled through seed cleaning and a rotation of 3-4 years.

L. usitatissimum attracts 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; the larvae of flea beetles ( Aphthona euphorbiae and Longitarsus parvulus ) can damage roots while the adults feed on leaves, stem and seed; the caterpillar of Heliothis spp. penetrates the young seed bolls 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 graze on (and remove) the growing point of young plants, 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.

Harvesting

The optimum time for harvesting textile flax is when the straw is 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 can be done by hand, lifting and binding the straw into sheaves, which are left to dry and, if conditions are suitable, ret in the field, before being collected and stored under shelter. This process is labour-intensive and in most producing countries harvesting is done mechanically with pulling machines, which pull and lay the crop on the ground in swathes. The seed-bearing capsules can be removed during pulling or left on the plant during retting and baling and removed in the processing factory ("rippling"). Subsequent threshing of the seed is usually done concurrently with "scutching" of the fibre.

Industrial flax or dual purpose crops are often harvested with conventional combine harvesters to avoid the cost of specialized pulling and turning equipment. Successful combining of the seed requires a seed moisture content of 10-15%. Recent advances have been made in the development of mobile decorticators/harvesters which simultaneously pull, separate and bale the bark fibre in one pass with the core returned as mulch to the soil. Manufacturers claim success both with retted and unretted stem material. This mechanically decorticated fibre is usually of a poorer quality than that required for textile production and is typically used for paper manufacture.

Yield

Average world flax (fibre and tow) yields in 1996-2000 were estimated at about 1 t/ha per year and average world linseed yields at 0.8 t/ha per year. In an experiment with 7 flax cultivars in Tasmania (Australia), stem yields ranged from 4.7-8.8 t/ha, bark yields from 1.3-2.6 t/ha and seed yields from 1.6-2.2 t/ha. In Indonesia, experiments with 12 cultivars and 3 sowing dates resulted in an average yield per cultivar ranging from 2.0-3.9 t/ha dry stems and 0.2-0.5 t/ha dry seeds, whereas dry stem yields up to 7.8 t/ha were obtained in a plant density experiment.

Handling after harvest

Retting is most commonly performed in the field in a process called "dew retting". The duration and uniformity of dew retting depends on weather conditions. Ideally, harvesting needs to be followed by rain and periods of 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 carefully turn the crop to expose the underside of the crop. Turning can be done up to 3-4 times depending on crop yield. Once 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 these 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. Residual core is then removed via a process known as "scutching". The separated bark fibre is "hackled" by passing the fibre through a series of comb-like devices of increasing fineness, comprised of metal teeth that scrape and buff the fibre. The end products are "line flax", ready to be spun into yarn and subsequently used in textile manufacture, and "tow", the by-product of hackling often used in the manufacture of paper and other industrial applications. In the past these processes were performed manually but they are now generally mechanized. Flax fibre quality is usually assessed by visual and manual evaluation, whereas yarn quality is evaluated with the help of instruments, measuring strength, elongation, evenness, etc.

Harvested linseed can be dried, cleaned and stored using the same equipment and techniques used for other grain crops. A safe seed moisture content for long-term storage is 9% and below.

Genetic resources

L. usitatissimum does not seem to be threatened with extinction owing to its widespread cultivation. Large germplasm collections are kept in France (Institut National de la Recherche Agronomique (INRA), Versailles), Belgium (Gembloux), the Netherlands (Centre for Genetic Resources (CGN), Wageningen), Germany (Bundesforschungsanstalt für Landwirtschaft (FAL), Braunschweig), the United States (United States Department of Agriculture (USDA), Beltsville) and the Russian Federation (N.I. Vavilov Research Institute of Plant Industry, St Petersburg).

Breeding

The breeding objectives for L. usitatissimum vary with the end use of the crop. As fibre yield is strongly influenced by management and environmental factors, breeders use fibre content or fibre wealth (the ratio of fibre weight to total stem dry weight) as breeding objectives. Fibre quality is particularly important for flax grown for textile fibre, and quality traits that have been bred for include 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.

For dual purpose flax, seed yield and oil content are key considerations. Seed quality breeding has largely focused on fatty acid composition and has led to the development of the low-linolenic acid Linola cultivars. Some efforts have been made to breed these low-linolenic acid characteristics into a fibre type of flax. In cultivars developed for non-food purposes, on the other hand, the linolenic acid content needs to be high.

Substantial breeding efforts have been made to improve lodging resistance via straw stiffness and fibre content. In the absence of chemical control methods for Fusarium wilt, breeding efforts have been focussed on developing disease resistance, with limited success to date. Breeding for tolerance or resistance to various pests has not received much attention, principally because of the availability of effective insecticides. Given the severity of weed competition often experienced in flax crops, efforts have been made to screen new cultivars for herbicide tolerance and to incorporate herbicide resistance genes.

The breeding objectives described above are difficult to achieve via conventional breeding methods because the traits involve polygenically inheritance, low heritabilities and unreliable assessment techniques. Consequently, a range of biotechnological techniques are being employed to supplement classical breeding, including somaclonal variation, in vitro selection, anther and microspore culture, protoplast culture, genetic mapping and recombinant DNA technology.

Prospects

Worldwide, L. usitatissimum is going through somewhat of a resurgence after a period in which it was felt that the development of synthetic fibres and drying agents within the petroleum industry might bring about the extinction of the crop. This resurgence can be attributed to a range of factors, including:

• the fact that flax is seen as a suitable alternative to overproduced food crops in the European Union, with subsidies to encourage flax production;

• a trend towards "environmentally friendly" and natural textiles;

• the development of stronger, more fashionable linoleum products at a competitive price to vinyl;

• new markets for oilseed flax straw in construction and fertilizer formulations;

• the development of genetically modified (GM) oilseed cultivars, rich in linoleic acid and with a fatty acid profile comparable to premium sunflower oil.

L. usitatissimum is grown commercially from 22-65N and 30-45S; the extremes of these latitudes are not noted for high fibre or seed yields. The apparent lack of suitable genotypes for the high temperature and rainfall conditions in South-East Asia suggests that flax has limited potential, at least not without substantial investment in a breeding programme to develop better adapted cultivars. However, there may be some scope for flax production at higher altitudes, e.g. in Java. The high cost of machinery for harvesting and processing flax fibre is likely to be a further impediment to flax development in this region.

Literature

• Abdullah, A., Tridjatiningsih & Pribadi, E.R., 1986. Pertumbuhan beberapa varietas linum di berbagai altitude [The growth of flax cultivars at different altitudes]. Pemberitaan Penelitian Tanaman Industri 11(3-4): 41-45.
• Berger, J., 1969. The world's major fibre crops: their cultivation and manuring. Centre d'Etude de l'Azote, Zürich, Switzerland. pp. 209-216.
• Dempsey, J.M., 1975. Fiber crops. The University Presses of Florida, Gainesville, United States. pp. 3-45.
• Lisson, S.N. & Mendham, N.J., 2000. Agronomic studies of flax (Linum usitatissimum L.) in south-eastern Australia. Australian Journal of Experimental Agriculture 40(8): 1101-1112.
• Marshall, G., 1993. Recent developments in flax breeding relevant to production technologies. Industrial Crops and Products 1: 273-281.
• McHughen, A., 1992. Revitalisation of an ancient crop: exciting new developments in flax breeding. Plant Breeding Abstracts 62(10): 1031-1036.
• Sultana, C., 1983. The cultivation of fibre flax. Outlook on Agriculture 12(3): 104-110.
• Suratman & Emmyzar, 1980. Linum (Linum usitatissimum L.) serta kemungkinannya di Indonesia [Flax and its prospects in Indonesia]. Pemberitaan Lembaga Penelitian Tanaman Industri 37: 45-62.
• Suratman & Emmyzar, 1982. Hasil percobaan waktu tanam dan umur panen pada tanaman linum [Results of experiments on the dates of planting and harvesting of flax]. Pemberitaan Penelitian Tanaman Industri 8(42): 45-49.
• Toxopeus, H.J., 1938. Ervaringen met de vlascultuur in Nederlandsch-Indië [Experimental data on flax growing in the Dutch East Indies]. Korte Mededeelingen van het Algemeen Proefstation voor den Landbouw. No 21. Algemeen Proefstation voor den Landbouw, Buitenzorg, Dutch East Indies. 38 pp.
• Turner, J., 1987. Linseed law: a handbook for growers and advisors. BASF United Kingdom, Hadleigh, Suffolk, United Kingdom. 356 pp.
• Wood, I.M., 1997. Fibre crops: new opportunities for Australian Agriculture. Queensland Department of Primary Industries, Brisbane, Australia. pp. 17-24.

Authors

S.N. Lisson