Corchorus L. (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Corchorus L.

Protologue: Sp. pl.: 529 (1753), Gen. pl. ed. 5: 234 (1754).

Family: Tiliaceae

Chromosome number: x= 7;C. capsularis,C. olitorius: 2n= 14

Major species and synonyms

• Corchorus capsularis L., Sp. pl.: 529 (1753), synonyms: C. cordifolius Salisb. (1796), C. marua Buch.Ham. (1828).

• Corchorus olitorius L., Sp. pl.: 529 (1753), synonyms: C. quinquelocularis Moench (1794), C. decemangularis Roxb. (1814), C. catharticus Blanco (1837).

Vernacular names

• General: jute (En, Fr). India, Bangladesh: pata, jhot
• Philippines: saluyot, saluyut (Ilokano), pasau (Tagalog).

• C. capsularis : white jute, deshi jute (En). Chanvre de Calcutta (Fr)
• Indonesia: serani (Aceh), silangkang (Padang Sidempuan), ganja cina (Moluccas)
• Malaysia: jelita, kanching baju, senerong betina
• Philippines: pasau-na-bilog (Tagalog), tagabang (Bisaya)
• Cambodia: dok kah pha, krachav
• Thailand: seng, po seng (northern), pak kom
• Vietnam: day quả tròn.

• C. olitorius : tossa jute, Jew's mallow (En). Corète potagère (Fr)
• Indonesia: gedangan, pisangan (Javanese)
• Philippines: pasau-na-haba (Tagalog), lumhay (Bisaya)
• Thailand: krachao, po krachao (central), po krachao fak yao
• Vietnam: day, day quả dài.

Origin and geographic distribution

Corchorus is a pantropical genus comprising an uncertain number of species, with estimates ranging from 40-100. Most species are of African origin. The centre of origin of C. capsularis is the Indo-Burman region, including southern China. The primary centre of origin of C . olitorius is probably Africa, with India or the Indo-Burman region as a secondary centre. Both species are cultivated and have naturalized in many parts of the tropics, including South-East Asia.

"Korkhoros" is an old Greek name for C. olitorius long in use as a leaf vegetable in the Middle East and North Africa. In Asia and Africa jute has probably also provided fibre for cordage and woven cloth since ancient times. However, there is uncertainty about the time of its first domestication as a fibre crop, because historical references to cloth from plant fibres are not specific. The Sanskrit word "patta", for instance, may have originally included jute and other fibres as well. There is, however, evidence of trade in jute cloth in 16th Century Bengal. The cultivation of jute in India expanded considerably during the first half of the 19th Century, as a result of growing European interest in jute fibre as a suitable and cheaper substitute for hemp ( Cannabis sativa L.) and flax ( Linum usitatissimum L.) in the manufacture of cordage and packaging cloth. Exports of raw jute from Calcutta to England increased from 100 t in 1793 to 28 000 t by 1850. The introduction of jute spinning and weaving machinery, developed for the Scottish flax and jute industry during the 1830s, resulted in a rapid establishment of large numbers of power-driven jute mills and further expansion of jute cultivation in India. Ever since, world jute production and processing has been concentrated largely in the Ganges-Brahmaputra delta of India and Bangladesh, with minor areas of cultivation elsewhere in Asia. Jute was introduced into the states of Para and Amazonas in Brazil around 1930 by Japanese immigrants. India and Bangladesh produce jute from both species. C. olitorius is potentially higher yielding and produces a fibre of finer quality but C. capsularis is preferred for cultivation in lowland areas because of its tolerance to temporary inundation. C. capsularis is most commonly cultivated in all other jute producing countries. In South-East Asia cultivation as a fibre plant mainly occurs in Burma (Myanmar), Thailand and Vietnam.

Uses

Jute has been the most widely used packaging fibre for more than 100 years because of its strength and durability, low production costs, ease of manufacturing and availability in large and uniform quantities. About 50% of raw jute is processed into gunny bags and sacks for transportation and storage of agricultural and industrial commodities. Other traditional products include hessian cloth, carpet backing, yarn, twine, cordage, felt and jute carpets. Jute is a versatile natural fibre finding a wide range of new applications in fabrics for furniture, upholstery, soft luggage, wall coverings, laminated sheets for packaging boxes and panelling (as a substitute for plywood), as well as in geotextiles for erosion control on slopes and for agricultural mulching. Whole jute stems are suitable as raw material for paper pulp. However, when jute is used for pulping, it is usually in the form of cuttings from burlap manufacture, old sugar bags and wrappings. The resulting pulp is made into hard, thick paper, suitable for cards and labels. The woody central core or "stick" remaining after removal of the bast serves as rural building material, thatch, fences, fuel and for charcoal-making. It can also be processed into paper, board and cellulose.

The leaves and tops of C. olitorius are eaten as a vegetable, for instance in Malaysia, Indonesia and the Philippines. In Africa and the Middle East C. olitorius is mainly grown and used for this purpose, and not for its fibre. The leaves of C. capsularis are applied medicinally in Peninsular Malaysia to poultice sores, and in decoction they serve against dysentery, phthisis and cough, and as a tonic for children. In the Philippines the leaves of C. capsularis are used against headache. Though the seeds of both C. capsularis and C. olitorius are toxic, those of the former are recorded as being used, in the form of powder or in decoction, as a tonic, carminative and febrifuge in the Philippines, and those of the latter as a purgative.

Production and international trade

The world jute production in the period 1997-2001 averaged 2.76 million t raw fibre per year from 1.46 million ha. India (1.68 million t per year from 862 000 ha) and Bangladesh (852 000 t per year from 474 000 ha) together produced more than 90%. Jute cultivation is very labour intensive and for that reason it is typically a smallholder crop. The flood plains in the lower delta of the Ganges and Brahmaputra rivers combine optimum conditions for jute cultivation (with respect to climate, soil, and adequate surface water for retting) with the availability of inexpensive farm labour. Other countries with noticeable jute production in 1997-2001 were China (125 000 t per year), Burma (Myanmar) (36 000 t), Uzbekistan (20 000 t), Nepal (15 000 t), Vietnam (14 000 t) and Thailand (4900 t). The average annual jute production in Cambodia was only about 800 t in this period.

Most jute fibre is processed within the producing countries. In 1997-2001 world raw jute fibre exports amounted to about 350 000 t per year, and were almost entirely from Bangladesh. Thailand imported on average 17 000 t annually and Indonesia 5000 t. The annual export of manufactured jute products is about 630 000 t per year, 70% from Bangladesh and 25% from India. Exported products include new gunny bags (50%), yarn (20%), hessian cloth (15%), carpet backing (10%) and smaller quantities of twine, cordage, felt, carpets and other products.

Properties

Jute fibres are obtained from the bast of C. capsularis and C. olitorius , where they occur in the form of wedge-shaped bundles. Dry matter partitioning in a fully-grown jute plant is on average: bark 26% (16% fibre and 10% retting waste), wood 47%, leaves 19% and roots 8%. The spinnable units in jute fibre strands are, like those in most other bast fibre crops, filaments composed of a string of cells cemented together by pectin and hemicelluloses. Individual fibre cells are (0.5-)2-2.5(-6.5) mm long, with a diameter of (9-)15-20(-33) μm. The length of the fibre cells decreases from the top to the bottom of the stem, whereas the width increases. The lumen width varies greatly throughout the length of the fibre cell, with the lumen sometimes closing up. Dislocations and cross-markings are faint. The fibre ends show great variation, with spoon-shaped ends being characteristic for jute. The filaments in yarns ready for spinning can vary in length from 1-250 mm. The use of jute is limited to coarse fabrics, because the length:diameter ratio of jute filaments is only 100-120, much below the minimum of 1000 required for fine spinning quality. Jute fibre is hygroscopic and wetted filaments may swell up to 23% in diameter. Typical values of the tensile strength, elongation at break, and Young's modulus of jute fibre are 395-775 N/mm², 1.5-1.8% and 26.5 GPa, respectively. The rather low ignition temperature (193°C) of jute fibre poses a considerable fire hazard in warehouses. Jute fibre contains 45-64% α-cellulose, 12-26% hemicelluloses, 11-26% lignin, 0.2% pectin and 1-8% ash. The fibre of C. olitorius is finer, softer and more lustrous than that of C. capsularis . The former is yellowish to reddish and the latter usually whitish. Jute fibre may be treated with a strong alkali ("woollenization"), resulting in a reduced fibre length, a softer feel and a crimp or waviness, giving the fibre a wool-like appearance. Woollenised jute is used for cheaper rugs and, blended with cotton, for decorative cloths, curtains and upholstery.

The woody central core is of medium durability under exposed conditions. The fibres in the central core are 0.5-0.8 mm long and 29-42 μm wide.

The seeds of C. capsularis and C. olitorius are poisonous to mammals and insects. They contain cardiac glycosides (often based on strophanthidin (corchorin) and digitoxigenin), which have digitalis-like effects on the heart. In an experiment, a methanolic extract of C. olitorius seed and its glycoside fraction were toxic when administered intraperitoneally, but showed little acute toxicity when administered orally. The leaves of C. capsularis have a bitter taste due to the presence of glycosides, though non-bitter cultivars exist. The leaves of C. olitorius contain only very small amounts of glycosides and are not bitter. The leaves of C. olitorius have shown antioxidative properties, and various antioxidative phenolic compounds have been isolated from them. Jute seeds contain 14-18% oil, with the major components being linolenic acid (41-43% for C. capsularis and 62-66% for C. olitorius ), oleic acid (29-37% and 9-13%) and palmitic acid (12% and 16-24%).

The 1000-seed weight (6-8% moisture content) is 3.3 g for C. capsularis and 2 g for C. olitorius .

Adulterations and substitutes

The fibres of kenaf ( Hibiscus cannabinus L.) and roselle ( H. sabdarrifa L.) are coarser and cheaper than jute. They are acceptable substitutes for jute in the manufacture of coarse packaging fabrics, but a mixture of jute with either of these fibres sold as pure jute is considered an adulteration. Other bast fibres which can serve as substitutes for jute include those from Abroma augusta (L.) L.f., Helicteres isora L., Malachra capitata (L.) L. and Urena lobata L. Since the second half of the 20th Century jute has faced substitution as sack making material by synthetic fibres such as polypropylene.

Description

Annual herbs or perennial shrubs, often with simple or stellate hairs. Taproot up to 60 cm deep with many lateral roots, adventitious roots on lowest stem section. Stem slender, cylindrical, 0.7-3.6 cm diameter at base, light to dark green or dark red, in cultivation unbranched in vegetative stage, branched near the top on flowering plants. Leaves alternate or spirally arranged, herbaceous; stipules small, caducous; blade simple, serrate to dentate, one or two lowest teeth often enlarged. Inflorescence a lateral or leaf-opposed, 1-several-flowered umbellate or racemose cyme; flowers bisexual; sepals 4-5, free, sometimes hooded at apex, often apiculate or caudate at apex; petals 4-5, yellow, usually shortly unguiculate; androgynophore usually present, at apex with a fleshy, annular to cup-like disk; stamens 4 to numerous, free, filaments terete, anthers dorsifixed; ovary 2-10-locular; ovules 2-many per loculus; style terete, stigma minutely lobed or toothed, fimbriate. Fruit a capsule, 2-10-valved, cylindrical to subglobose, with several seeds per loculus. Seedling with epigeal germination.

• C. capsularis . An erect herbaceous annual, 1-2.5 m tall (up to 4 m in cultivation), base often becoming woody, branching near the top with glabrous, terete branchlets. Leaves with linear-ovate stipules 0.5-1 cm long; petiole 0.5-3 cm long, pubescent above; blade narrowly ovate to elliptical, 5-14 cm × 1-6 cm, base rounded, margin serrate with 2 lower teeth prolonged into fine pointed auricles up to 1 cm long, apex acuminate, glabrous above, minutely papillose below. Inflorescence lateral, solitary at nodes, 2-3-flowered; peduncle 1-2 mm long; pedicel 0.5-1.5 mm long, erect in fruit; sepals 5, linear-obovate, 3-4 mm × 1-1.5 mm, hooded, apex apiculate; petals 5, obovate, 4-4.5 mm × 2.5 mm, claw 1 mm long; androgynophore 0.1 mm long, annulus 0.5 mm long, crenate; stamens 20-25, filaments 2.5-3 mm long; ovary obovoid, 10-celled with 10 ovules per cell; style 1-1.5 mm long, stigma 5-toothed. Fruit depressed globose, 1-1.5 cm in diameter, longitudinally sulcate, coarsely verrucose, 10-valvate, with 35-50 seeds. Seed rhomboid to obovoid, about 2-3 mm long, dark brown.

• C. olitorius . An erect herbaceous annual, 1-2.5 m tall (when grown as a fibre plant taller than C. capsularis , when grown as a vegetable a well-branched herb up to about 30 cm tall), base often becoming woody, branching near the top with glabrous, somewhat angular or sulcate branchlets. Leaves with setaceous stipules 7-12 mm long; petiole 0.5-6 cm long, pubescent above; blade narrowly ovate to obovate, 3-12 cm × 1-5 cm, base rounded, margin serrate with 2 lower teeth prolonged into fine pointed auricles up to 1.5 cm long, apex acuminate, glabrous or with short simple hairs below. Inflorescence leaf-opposed, solitary at the nodes, 1-3-flowered; peduncle up to 1 mm long; pedicel 2 mm long, erect in fruit; sepals 5, linear-obovate, 6-8 mm × 2 mm, apex with 1 mm long point, glabrous outside, pubescent inside near base; petals 5, narrowly obovate, 6-7 mm × 2 mm, claw 1 mm long, finely ciliate at margin; androgynophore up to 0.5 mm long, annulus 0.2 mm long; stamens 30-50, filaments 3-4 mm long; ovary cylindrical, 3-3.5 mm long, 5-6-sulcate, covered with small stiff ascending hairs, 5-6-celled with 36-42 ovules per cell, style 1-2 mm long, stigma lobed. Fruit somewhat appressed to stem, cylindrical, 3-8 cm × 3-6 mm, straight, longitudinally 10-12-ribbed, glabrous, 5-6-valved, apex undivided-acuminate 5-10 mm long, with 130-200 seeds. Seed rhomboid, about 1-2 mm long, somewhat rugose, bluish green to black.

Growth and development

Mature jute seeds have no dormancy. In warm and moist soil the radicle emerges from the seed within 24 hours after sowing and a plumule with cotyledons surfaces within 5-7 days. Initial growth is rather slow and 30-day-old seedlings are only 35-45 cm tall (dry weight of 3 g per plant). Subsequent growth accelerates considerably: to an average height of 150 cm at 60 days and, for cultivars with medium-late crop duration, 290-300 cm (dry weight of 75 g per plant) at 120 days, when these cultivars start flowering. C. olitorius generally shows higher growth rates than C. capsularis . In both species the duration from sowing to flowering may vary from 82-97 days (early cultivars), 102-109 days (medium cultivars), 124-128 days (late cultivars) to 148-154 days (very late cultivars). Most nodes on the main stem carry axillary buds, but close spacing in cultivation promotes straight vertical growth without lateral branching during the vegetative phase. Forking of the apex into 2 or more branches marks the transition to the reproductive phase. Subsequently, a number of axillary buds below and above the point of forking may sprout into laterals. Inflorescences are borne mainly on the terminal part of the main stem and upper laterals. Flushes of flowering usually last 4-6 weeks in C. capsularis and may last up to 10 weeks in C. olitorius . In C. capsularis anthesis starts 1-2 hours after sunrise and natural cross-pollination is usually less than 5%. Anthesis in C. olitorius starts 1 hour before sunrise and outcrossing may be 12% or higher due to larger flowers which remain open over a longer period of time. Cross-pollination is mainly by bees and other insects. Seeds mature within 6 weeks after anthesis. During the reproductive phase the leaves on the main stem turn yellow and abscise, leaving only some smaller green leaves on the upper part of the plant. When most seeds are mature the plant dries up and dies, some 200-220 days after sowing for a standard jute crop in India or Bangladesh.

In Java wild plants of both species flower year-round. In Thailand wild C. olitorius flowers and fruits from August to December.

Other botanical information

Confusion exists about the number and delimitation of species in Corchorus , and a worldwide taxonomic revision is needed. It is the only genus with herbaceous representatives in Tiliaceae . Numerous cultivars exist of the 2 species treated here, mostly differing in agriculturally important characteristics. In C. olitorius 2 major cultivar groups can be distinguished: one group of cultivars is grown particularly for their use as a vegetable, the other group for their use as a fibre plant. Although C. capsularis and C. olitorius resemble each other closely, they can be distinguished easily by their fruits, which are subglobose in the former and cylindrical in the latter.

So far, 21 Corchorus spp. have been confirmed as diploids with 2 n = 14 chromosomes, similar to the two cultivated species. A few tetraploids are known, such as C. junodii N.E. Brown from Mozambique. Strong crossing barriers between species prevent introgression from wild to cultivated species. Artificially (colchicine) induced tetraploids in cultivated Corchorus species always have lower fibre yields than diploid cultivars.

Anthocyanin pigmentation of the stem and leaves is controlled by 3 major genes: C-c, pigmented versus green; an allelomorphic gene, Ad-Ar-An-A-a, determining the intensity of pigmentation; and a pigment-reducing factor R-r (reducing versus non-reducing). Stem pigmentation is an important characteristic used to distinguish among cultivars. One major gene determines the bitter taste of leaves: Br-br (bitter versus non-bitter). The non-branching characteristic in a C. capsularis cultivar of Sudanese origin is controlled by the recessive allele of gene Br-br. Unfortunately, non-branching appears to be linked to disease susceptibility.

Ecology

Jute is mainly grown between 16N and 27N, during the hot wet summer season. The daily temperature range for optimum growth is 22-34°C. Growth is retarded at temperatures below 17°C and above 42°C. The annual rainfall should be 1000-2000 mm, with 150 mm of pre-monsoon showers at sowing time in March-April, followed by a relatively dry period with a few light showers in May, and subsequently by the main monsoon rains (June-September). Young C. capsularis seedlings can withstand drought better, whereas C. olitorius is more tolerant of drought in advanced stages of development. All young jute plants are sensitive to waterlogging, but large C. capsularis plants are tolerant of temporary inundation. A relative humidity of 65-90% is most beneficial for the crop. Jute is a short-day plant, with a prolonged vegetative phase where photoperiods are longer than 12-12.5 hours, but the degree of photoperiod sensitivity differs between cultivars and photoperiod-insensitive mutants of both C. capsularis and C. olitorius have been developed. Flowering is induced within 15-20 days in response to short daylengths after the middle of August.

Jute can be grown on a range of soils from clays to sandy loams provided they are deep, free-draining, fertile and with a pH between 5 and 8.6 (optimum pH 6.6-7). Jute, more in particular C. capsularis , is tolerant of fairly saline soils (maximum 1% salt content). Sandy soils increase the risk of wilting of young crops in the case of late starting monsoon rains. Most C. capsularis is grown on soils of alluvial origin, especially those of river banks that are inundated every year and enriched by deposits of silt, while C. olitorius is generally planted on upland soils.

In South-East Asia C. capsularis grows wild in open grassland, waste places, arable land and along watercourses up to 300 m altitude. C. olitorius is found as a weed in settled areas, for instance on fallow or waste fields, grassland, open spaces and paddy fields, up to 300 m altitude.

Propagation and planting

Jute is propagated by seed. Vegetative propagation by terminal cuttings is possible and sometimes applied to obtain seed of selected plants or to produce breeder seed of new cultivars. Jute seed is hygroscopic and germination may be poor after six months of storage under humid conditions. However, seeds properly dried after harvesting (6-8% moisture content) and stored in airtight containers will retain high viability (more than 80% germination) for 2-3 years even at ambient temperatures of 24-30°C.

Jute is sown directly in the field. In the main jute belt of India and Bangladesh this is done during March-April. In Cambodia C. capsularis is sown either in May, as a wet season crop, or in February, as an irrigated dry season crop. In the Philippines it is recommended that jute be sown in April-June. The small jute seeds require a fine seed-bed, which is achieved by repeated ploughing and cross-ploughing followed by laddering (harrowing with a log of wood or bamboo ladder weighted down by the cultivator standing on it) to pulverize and level the soil and also to remove weeds. The first round of ploughing should break up the soil to a depth of at least 40 cm, as jute is a rather deep rooter. Organic manure (composted domestic refuse or water hyacinth, cow dung, rapeseed or castor cake) may be ploughed in when available. Manuring is not needed when jute is grown after a potato crop (residual soil fertility of the previous crop) or in fields which are silted annually by floods. Most jute crops are still sown by broadcasting at seed rates of 7-13 kg/ha for C. capsularis and 4-9 kg/ha for C. olitorius . Seeds are often mixed with sand to ensure a more even distribution. Immediately after sowing, the seed is covered with soil to a depth of 2-3 cm by harrowing and laddering. Broadcast seeded plots require thinning to a final density of 330 000-440 000 plants per ha. Row planting (30 cm between and 7-8 cm within row spacing) has many advantages: 50% lower seed rates, fewer rounds of thinning and weeding, opportunities to reduce costs by utilizing mechanical implements for sowing, thinning and weeding, more convenient harvesting and generally higher fibre yields. However, it is still not widely practised by South Asian jute growers.

Seeds can be produced on plants left in a corner of the field after harvesting the main crop. However, seed yield and quality are generally low and the longer growth duration interferes with subsequent cropping. Therefore, most jute seed is produced in special plots sown in April or in September on uplands to avoid flooding. Late sowing is becoming general practice because the short days of October induce profuse branching and flowering in the young jute plants, resulting in higher seed yields. Seed quality is also better, because harvesting takes place during the cool dry winter season.

In vitro propagation of jute is possible: multiple plants have been regenerated from cotyledons and shoot tips of both C. capsularis and C. olitorius .

Husbandry

The traditional method of broadcast sowing at high seed rates results in a quick coverage of the soil by a thick stand of young jute plants, provided seed viability is adequate. This suppresses weed growth and also avoids the risk of insufficient crop density after high plant mortality due to failing pre-monsoon showers. Jute grown in this way requires 3-5 rounds of thinning and weeding during the first 2.5 months, which is mostly a manual operation involving about 80-100 man days per ha and accounts for about one-third of the total costs of fibre production.

Nutrient requirements depend on initial soil fertility and yield levels. Responses in fibre yield of 30-200% to N fertilizer applications (25-70 kg N/ha) have been found, without substantial responses to other nutrient applications. However, the uptake per ha of a C. capsularis crop, based on 34 t/ha green plants and 2 t retted fibre, is considerable for all major nutrients: on average 63 kg N, 14 kg P, 132 kg K, 71 kg Ca and 26 kg Mg. The lack of response to other nutrients than N is explained by the fact that most soils in the jute belt of India and Bangladesh are deficient in N but high in P, K and other major nutrients. Very few smallholders have the financial means to apply inorganic fertilizers to their jute plots. In seed production it is more common to apply N, P and K fertilizers, as increases in seed yield are generally significant for all three nutrients and the economic value of jute seed is high.

Jute is basically a rainfed crop, but supplementary irrigation during the early stages of crop development can improve fibre yield considerably.

Diseases and pests

The fungus Macrophomina phaseolina is the principal pathogen in both jute species, causing seedling blight, collar rot and stem rot, whereas its sclerotial stage ( Rhizoctonia bataticola ) causes root rot. Hooghly wilt in India may result in crop losses of up to 40% by the combined action of Rhizoctonia bataticola , Fusarium solani , the bacterium Ralstonia solanacearum and the nematode Meloidogyne incognita . Methods of control include seed treatment, crop rotation, avoiding acid soils (pH < 6.6) and excessive N applications, and the use of less susceptible cultivars. Other major diseases are anthracnose ( Colletotrichum corchori on C. capsularis and Colletotrichum gloeosporioides on C. olitorius) , soft rot ( Sclerotium rolfsii , synonym: Corticium rolfsii ), black band disease ( Botryodiplodia theobromae ). Diseases of minor importance include leaf spot ( Cercospora , Helminthosporium and Phyllosticta spp.), tip blight ( Curvularia subulata ), stem gall ( Physoderma corchori ), mildew ( Oidium sp.) and a virus causing leaf chlorosis or mosaic (seed borne and transmitted by white fly, Bemisia sp.).

Root-knot nematodes ( Meloidogyne incognita and M. javanica ), sometimes with secondary infection by Macrophomina phaseolina , can cause severe damage to jute crops. Methods of control include deep ploughing, removal of plant debris, proper drainage, avoidance of cropping sequences involving alternate hosts of the nematodes and the use of less susceptible cultivars.

About 40 insect species attack jute in India and Bangladesh, causing considerable yield losses and often adversely affecting fibre quality. The main insect pests are the jute apion or jute stem weevil ( Apion corchori ), the jute hairy caterpillar ( Spilosoma obliqua ), the jute semilooper ( Anomis sabulifera ), the indigo caterpillar ( Spodoptera exigua ) and the mole cricket ( Brachytrypus axhanitus , synonym: B. portentosus ). The indigo caterpillar is an important pest mainly of young seedlings. Mealybugs ( Pseudococcus virgalatus ) may attack C. olitorius particularly late in the growing season. Parasitization can be an important factor in natural control of the above-mentioned insect pests, particularly in the case of the jute apion and semilooper. This calls for judicious application of insecticides. The hairy caterpillar can be effectively controlled by hand picking. An old but effective method of natural control of the semilooper is the erection of perches in the jute field to attract predatory birds. Mites can be a problem during dry weather. C. olitorius is more susceptible to yellow mite ( Hemitarsonemus latus , synonym: Polyphagotarsonemus latus ), whereas the red mite ( Oligonichus coffeae ) occurs only on C. capsularis .

Harvesting

Jute is generally harvested between 100 and 120 days after sowing when most plants are flowering. Earlier harvesting will result in lower yields of immature, finer fibres, whereas later harvesting will produce higher yields of coarse low-quality fibre that requires longer retting. Jute is normally harvested by hand with a sickle, being cut at the base of the stem very close to the soil surface. Thick- and thin-stemmed plants are usually sorted into separate groups (for uniform retting) before stacking them vertically for 2-3 days in the field to induce defoliation and desiccation. After shaking off all remaining leaves the stems or "reeds" are tied with bark strips into bundles 15-20 cm in diameter. The leaf-shedding operation is not possible if the crop is harvested on flooded land. In that case, the leaves are stripped off directly after harvest.

Yield

The world average jute yield is about 1.9 t of raw fibre per ha. National averages are 1.8 t/ha for Bangladesh, 2.0 t/ha for India and 2.2 t/ha for China. Yields of 3.0-5.0 t/ha have been obtained in field experiments in Bangladesh with improved cultivars grown under optimal agronomic conditions. The estimated dry fibre yield in Cambodia is 1 t/ha. In Borneo in the 1940s and in Peninsular Malaysia in the 1950s fibre yields of 0.8-1.1 t/ha were obtained with C. capsularis cv. Segama. In experiments in Java and Sumatra fibre yields up to 2.3 t/ha have been obtained. Seed yields vary from 100-250 kg/ha in early sown to 400-1200 kg/ha in late sown multiplication blocks.Potential fibre and seed yields are generally higher for C. olitorius than for C. capsularis cultivars.

Handling after harvest

Jute stems are retted in water for a period of (8-)15-20(-30) days to free the fibres from the surrounding bark tissues by enzymatic action associated with microorganisms. The length of the retting period is of critical importance: if it is too short, the fibre is difficult to remove and clean; if it is too long, the fibres are damaged and of lower quality. Retting of both species is most rapid at a water temperature of 34°C, but the resulting fibre is harsher and less bright than when retted at lower temperatures. Rafts (India: "jak") consisting of 2-3 layers of stem bundles are steeped in the shallow water of canals, ditches or ponds. Slowly moving water helps to remove the acidic and dark-coloured degradation products and produces the best quality fibre. When retting is complete, the fibres are stripped manually from the stems and washed in clean water to remove all remaining gum, decomposed plant tissues and dirt. The clean fibres are then dried in the sun over bamboo racks for 3-5 days. The quality of jute fibre is to a large extent determined by correct retting, cleaning and drying. Ribbon retting, whereby the bark is stripped from freshly harvested stems by manual or machine decorticators and only the ribbons steeped in water, requires less water and reduces the retting time by half. It is a method that has generally been used in China and it is gradually being introduced in India and Bangladesh, particularly in areas with chronic water shortage during the retting season. The dried fibres are transported in crude bales to local centres for initial grading and packing into low compression "kutcha" bales of 60-150 kg before transportation to the jute spinning mills. Raw jute for export is carefully graded and cleaned (e.g. removal of coarse butt ends) before packing by hydraulic presses into compact "pucca" bales with standard weight of 180 kg each. Grading systems vary among countries: Indonesia and Thailand have only 3-4 grades, whereas Bangladesh, India and Nepal have 6-8 grades each for C. capsularis and C. olitorius . The principal characteristics used in grading are length, strength, colour, lustre, cleanliness, uniformity and the percentage of "roots" (bark fibres from the basal part of the stem).

In almost all jute-producing countries a part of the jute harvest is not retted, but ribboned, scraped with a knife and dried. The resulting ribbons are used as tying twine or as raw material for the production of yarns and rope.

Pulping of waste material such as burlap pieces and old bags is primarily done with chemical processes such as the soda process. Retted fibre can be satisfactorily pulped with the refiner mechanical pulping (RMP) process; treatment with the white rot fungus Ceriporiopsis subvermispora prior to refining results in considerable energy savings and increased strength properties. Unretted bast fibre has been experimentally pulped using the neutral sulphite-anthraquinone (NS-AQ) process, but yields were low and the input of chemicals high, compared to the pulping of retted fibre. The central cores can be pulped with various chemical and chemi-mechanical processes. Pulping experiments with whole stems showed that the soda-amine process (soda process with amines as additives) gave higher yields and better physical properties than the soda and kraft processes.

Genetic resources

Early efforts to collect, conserve and characterize local and exotic jute germplasm were initiated in Dhaka in 1904. The genebank of the Bangladesh Jute Research Institute (BJRI) in Dhaka was given the mandate of world repository for germplasm of jute and allied fibres by the International Jute Organization (IJO) in 1987. Since that time the total collection has been extended from 2100 to almost 6000 accessions at the present time, through various germplasm collection projects in Asia and East Africa. These include old and new cultivars, landraces, induced mutants, genetic and cytogenetic stock, and wild species. Some 2370 accessions represent C. capsularis , 1440 accessions represent C. olitorius , and 2190 accessions are of the allied fibre plants kenaf and roselle. A duplicate set of seed samples for all accessions is stored at the Commonwealth Scientific Industrial Research Organization (CSIRO) in Canberra, Australia. Jute research centres in India, China, Nepal, Thailand, Indonesia and other jute-producing countries have unrestricted access to genetic resources present in the genebank of the BJRI. The Central Research Institute for Jute and Allied Fibres (CRIJAF) in Barakpur (India) maintains a collection of more than 2300 jute accessions.

Breeding

Selection and breeding methods common to self-pollinated crops have been applied to jute. Most cultivars are the result of line selection within landraces and cultivars, or of intervarietal crossing within the same species. C. capsularis and C. olitorius are complementary in a number of agronomic characteristics. The first successful interspecific crosses between C. capsularis and C. olitorius were realized in 1960, but breeding programmes based on hybridization between the two species have not yet produced superior cultivars. Jute selection with the objectives of higher yields and finer fibre quality was started in Dhaka in 1904 by the Department of Agriculture of (British) India. Cultivars developed by this programme include C. capsularis cv. D154 (selected from the earlier "Kakya Bombai") and C. olitorius cv. Chinsurah Green, both released around 1919 and the main cultivars grown until 1952. After 1947 jute breeding activities continued at two locations: the BJRI (formerly Jute Agricultural Research Laboratories) at Dhaka and the Jute Agricultural Research Institute (JARI) at Barakpur in India. In addition to yield, fibre quality and disease resistance, early crop maturity and low photosensitivity (i.e. no premature flowering in early sowings) became important objectives of crop improvement, in order to fit jute into more intensive crop rotation schemes. Early sowing of jute in February (day-length less than 12 hours) will allow 3 crops per year, e.g. first jute, then rice and finally pulses or rapeseed. Examples of improved C. capsularis cultivars are "CVE-1" (released in 1977), "CC-45" (1979), "BJC-83" and "BJC-7370" (both 1995) in Bangladesh, and "JRC-212" (1951), "JRC-321" (1952) and "JRC-7447" (1967) in India. Examples of successful C. olitorius cultivars are "O-9897" (released in 1987) and "OM-1" (1995) in Bangladesh, and "JRO-632" (1952), "JRO-7835" (1971) and "JRO-878" (1980) in India. The cultivars grown in China, Burma (Myanmar), Thailand, Indonesia and other countries are mostly derived from introductions from India.

Prospects

Under pressure from food and other crops, jute cultivation is being pushed onto marginal land in almost all jute-producing countries. It is also finding strong competition from synthetic fibres in packaging materials and from the fact that agricultural commodities are increasingly shipped in bulk or in large containers. Nevertheless, jute fibres are a biodegradable and environment-friendly raw material suitable for many applications in various fabrics, semi-rigid and laminated sheets for packaging and panelling, as well as for the manufacturing of geotextiles. The biomass of jute plants can also be processed into pulp for the paper industry. The market for jute fibre could well expand in the future under the influence of growing concerns about environmental pollution and dwindling forest resources. Strategies in jute research and development will require further adjustment to include such targets as improved tolerance to suboptimal growing conditions and suitability of the plant and fibre to product diversification. Even with less photoperiod-sensitive cultivars the prospects for jute in South-East Asia are limited to production for local and national use, e.g. to substitute for imports in Thailand and Indonesia. It seems impossible for South-East Asia to compete in export markets, in view of the excellent ecological conditions for jute cultivation and the availability of inexpensive labour in Bangladesh and India.

Literature

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• Mahato, S.B., Sahu, N.P. & Roy, S.K., 1989. Cardiac glycosides from Corchorus olitorius. Journal of the Chemical Society, Perkin Transactions 1, 1989(11): 2065-2068.
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Authors

A.L. Khandakar & H.A.M. van der Vossen