Cyamopsis tetragonoloba (PROSEA)
Cyamopsis tetragonoloba (L.) Taubert
- Protologue: Engler & Prantl, Natürl. Pflanzenfam. 3(3): 259 (1894).
- Family: Leguminosae - Papilionoideae
- Chromosome number: 2n= 14
Cyamopsis psoraloides (Lamk) DC. (1825).
- Guar, cluster bean, Siam bean (En).
- Cyamopse à quatre ailes (Fr)
- Malaysia: kottavarai (Malayalam, Tamil).
- Burma (Myanmar): pè-walee, walee-pè
- Thailand: thua-kua (central).
Origin and geographic distribution
Guar is a cultigen of uncertain origin. It has been speculated that guar originated in north-western India and Pakistan from Cyamopsis senegalensis Guill. & Perr. The latter species, which occurs from Senegal to the Arabian Peninsula, is occasionally used as a fodder and may have been taken by Arabian traders to India as fodder for horses, which were one of their main trading commodities.
Guar was taken to Indonesia, Malaysia, and the Philippines around 1915. It is now grown in many parts of the drier tropics and subtropics. Introduced into the United States in 1903, it was developed into an industrial gum-producing crop during the second World War.
Traditionally, the main use of guar is as a green manure and cover crop, and as a shade plant for ginger and turmeric. Sweet and tender young pods are consumed as a vegetable in north-western and southern India. They are also eaten as snacks after drying and frying. Mature seeds have been eaten as a pulse during periods of food shortage. Guar is grown as a fresh or dry forage crop and as a feed-grain crop.
Guar seed is an important source of the industrial vegetable gum galactomannan, which has a thickening property 5-8 times stronger than starch. It is used as a thickener and stabilizer in foods such as salad dressings, ice cream, yoghurt, tinned vegetables and bakery items, and in the preparation of cheese and reconstituted tobacco. Industrially, guar gum is used to strengthen cloth and paper, as a filtering agent in the mining industry and as an additive to drilling fluids in oil-well drilling. The seedcake, a by-product of guar gum extraction, is an important source of animal feed, having a protein content of about 40%.
Extracts from guar seed are being tested as a medicine against non-insulin-dependent diabetes and against hyper-cholesteremia. Traditionally, leaves are eaten to cure night blindness, while pods are used as a laxative.
Production and international trade
The main area of production of guar as a green manure and fodder crop is north-western India and Pakistan. The main producers of guar for gum are India, Pakistan and the United States. Limited and fragmented information indicates that the annual production of guar seed in India for the period 1970-1975 was 510 000 t, which increased to 940 000 t in 1976. Pakistan produced 160 000 t in 1974. Annual production in the United States fluctuates strongly, from 35 000 t in 1976 to only 7000 t in 1978, averaging about 15 000 t. In 1987, world trade of guar gum stood at about 125 000 t. The United States is the main importer of guar gum supplied by India and Pakistan and imported about 45 000 t in 1994 at a price of 0.5 US$/kg.
Green pods contain per 100 g fresh material: water 82 g, protein 4 g, fat 0.2 g, carbohydrates 10 g, fibre 2.5 g, ash 1.5 g, Ca 0.1 g, P 0.25 g, Fe 6 mg, vitamin A 330 IU, vitamin C 50 mg. They contain 40-70 mg hydrocyanic acid per 100 g, which is removed by thorough boiling. The seed consists of 14-16% testa, 38-45(-50)% endosperm and 40-46% cotyledons. Dry seed contains per 100 g: moisture 10 g, protein 30 g, fat 2.5 g, carbohydrates 41 g, crude fibre 13 g, ash 3 g. The proximate composition of guar green forage is per 100 g: moisture 81 g, crude protein 3 g, digestible protein 2.5 g, ether extract 0.4 g, crude fibre 4.4 g, N-free extract 8 g, ash 3.3 g, Ca 0.6 g, P 0.07 g.
The galactomannan gum, which makes up 47-68(-85)% of the endosperm, consists of chains of D-mannopyranosyl units to which D-galactopyranosyl units are attached at every second unit. In cold water it forms a gel of exceptionally high viscosity at low concentrations. The viscosity depends on temperature and concentration. Maximum viscosity is achieved at 25-40 °C. Viscosity increases proportionally with concentration to about 0.5%. At higher concentrations it increases more slowly. Solutions are stable over a very wide pH range (pH 1-10) and a wide range of salt concentrations. With borate ions hydrated guar gum forms a cohesive, structured gel. Commercial guar gum is 78-82% galactomannan with some protein and other endosperm admixtures. In 1974 the United States Food and Drug Administration affirmed the "generally recognized as safe status" (GRAS) of guar gum, with specific limits.
The weight of 1000 seeds is 26-47 g.
- A robust, bushy, erect, annual herb, 20-100 cm tall in improved cultivars, up to 3 m in landraces. Root system well developed laterally.
- Stems and branches angular, grooved, appressed pubescent with white, forked hairs, sometimes glaucous; some cultivars remain unbranched.
- Leaves alternate, trifoliolate; leaflets elliptical to ovate, terminal one 8-12 cm long, lateral ones 5-8 cm long; rachis 3-7 cm long, pulvinate; margins toothed, the length of the teeth less than 1/10 of the breadth of the leaflet, which usually exceeds 1 cm.
- Inflorescence a dense, axillary raceme with 5-30 flowers.
- Flowers up to 9 mm long; calyx hairy, ending in 5 unequal teeth, carinal tooth longest; petals creamy white on emergence, changing through pink to light purple, standard orbicular, wings and keel oblong; stamens 10, filaments united into a staminal tube, anthers apiculate.
- Pod 6-12-seeded, 4-12 cm long, in stiff erect clusters, pubescent or glabrous, straight to slightly curved, beaked, with a single ridge at one suture and two ridges at the other.
- Seed hard, flinty, flattened, ovoid, about 5 mm long, white, grey or black.
- Seedling with epigeal germination.
Growth and development
After germination, about 3 simple leaves emerge, followed by compound leaves. Under controlled conditions, short daylength and high temperature delay the appearance of trifoliolate leaves and flowering may start before the first compound leaf appears. In branching cultivars most of the initial branching takes place near the stem base. Non-branching types have larger leaves than branched ones. Guar is a quantitative short-day plant, but cultivars in which flowering is not affected by daylength have been developed. Profuse and continuous flowering may start about one month after establishment. Flowers are cleistogamous, but in some cultivars natural crossing may be as high as 9%. Pod formation starts 45-55 days after sowing and peaks after 75-80 days. Seeds ripen 110-160 days after sowing.
Guar produces clusters of nitrogen-fixing nodules with Bradyrhizobium strains. Nodulation may start early, the first nodules becoming visible 1 week after germination.
Other botanical information
Cyamopsis DC. is a small genus of 3 species and is closely related to the genus Indigofera L. All species have a diploid chromosome number of 14. The 2 wild species are African (C. serrata Schinz) or mainly African (C. senegalensis).
Numerous cultivars of guar have been developed. In general, branched types are more suitable for seed production, while erect, single-stem types that produce larger and more fleshy pods are preferred in vegetable production. In India three main types are sometimes recognized: "Deshi", a mostly rainfed seed crop, 1.2-1.5 m tall; "Pardeshi", mainly grown for green pods, 1.5-1.8 m tall; and "Sotiaguvar", mostly grown for fodder and green manure, 2.5-3.5 m tall. "Sofia" is a multipurpose cultivar from Gujarat, grown as a green manure and shade plant and for its green pods, "Durgapura Safed" is a successful cultivar for forage and grain production. "Brooks" was the first cultivar released in the United States, moderately resistant to the main diseases (Alternaria leaf spot and bacterial blight). However, its resistance to bacterial blight tends to break down under heavy infestation, as is the case with "Kinman" released in 1974. "Mills" (early maturing), "Esser" (late maturing) and "Hall" (full season) were released in between 1965 and 1975, "Lewis" (intermediate) and "Santa Cruz" (full season) in 1985. These are all higher yielding than older cultivars and were more resistant to bacterial blight when released.
The American cultivars and "Pusa Sadabahar" and "Pusa Naubahar" from India are daylength neutral; most other cultivars are photosensitive.
Guar is a hardy, drought-tolerant legume. It grows in a wide range of environments from the sub-humid to semi-arid conditions in the tropics and subtropics with (300-)500-800(-1500) mm of rainfall. The main production of guar for seed occurs where annual rainfall is less than 800 mm. In areas with higher rainfall, vegetative growth is greater, but seed quality is inferior, making guar more suitable as a green manure and fodder crop. Guar prefers a very hot climate. Mean monthly maxima in northern India may reach 35-40 °C, though in southern India extremes are lower. Optimum soil temperature for root development is 25-30 °C. Guar is cultivated up to 900 m altitude. It is highly susceptible to frost. The optimum temperature for germination is about 30 °C. At 20 °C, germination is retarded, at still lower temperatures the rate of germination is reduced. It can grow in most soils, but thrives in well-drained alluvial and sandy-loam soils of pH 7.0-8.0. Waterlogging is not tolerated. On heavy soils, guar should be grown on ridges to maintain root aeration. In an experiment using irrigation water with equal amounts of NaCl and CaCl2, salinity levels up to 8.8 dS/m did not affect germination, early growth or grain yields.
Propagation and planting
Guar is propagated by seed. Scarifying the seed by mechanical means or by treating it with sulphuric acid tends to give more rapid and more uniform germination. However, under humid conditions germination is generally good without scarification.
For green manure production, seed is broadcast at a rate of 35-45 kg in India, versus 22-35 kg/ha in the United States.
In northern India, vegetable guar is generally grown twice per year, the first crop is sown after the start of the rainy season in June-July, the second crop is sown in February-March at the start of the hot season, and is grown under irrigation. In southern India, vegetable guar is grown throughout the year. In vegetable production, seeds are generally sown in raised beds, 5-7 cm deep at 45-60 cm × 22-30 cm or dibbled at 60 cm × 30-60 cm. The seed rate used ranges from 3-12 kg per ha.
For grain production in India, sowing is done in March-April under irrigation, while rainfed guar is sown soon after the onset of the monsoon rains in June-July. Seed is often broadcast, though sowing in rows gives higher yields. Spacing between rows varies from 30-60 cm, within-row spacing from 15-30 cm. Seed rates range from 10-15 kg/ha, but 12-25 kg/ha is also reported.
For grain production in the United States, guar is sown in rows 60 cm or 90-110 cm apart, at 10-30 cm within rows, using seed rates of 4-7 kg/ha. The recommended depth of sowing is 2.5-5 cm. Differences in seed rates reflect cultivar type and growing conditions rather than seed size.
Guar responds well to inoculation with rhizobium, which can improve nodulation by as much as 36%. Group E (cowpea) or Group PE inoculant are as good as specific guar inoculants.
In India, especially in dry areas, such as Gujarat, guar is often grown as an intercrop with other annuals such as pearl millet, sorghum, maize or cotton. It is also grown as a cover crop between young rubber or young coconut trees. As a sole crop it is grown in rotation with maize, sorghum, cotton, wheat and vegetables.
Guar plants cannot withstand much weed competition and inter-row weeding by chemical or mechanical means is needed. At least 2 mechanical weedings are normally required. In the United States the application of pre-emergence herbicides is recommended. Trifluralin and profluralin have been found to be non-toxic to guar. Alternatively, EPTC, chlorthal, naptalam or linuron can be used. Precautions should be taken if these herbicides are to be used when intercropping is practised. When grown as a vegetable, weeding is done manually.
The fertilizer requirements of guar are dependent on soil fertility. On fertile soils or soils well-fertilized in the previous season, guar hardly responds to fertilizer application. Otherwise, application of 30-50 kg/ha of P2O5and 10-15 kg/ha of K2O is recommended.
Although guar is adapted to rainfed agriculture, it responds well to irrigation. It has the ability to cease growth during dry weather and to sprout when rain resumes.
Diseases and pests
Internationally, bacterial blight, caused by Xanthomonas cyamopsidis and leaf spot caused by the fungus Alternaria cucumerina var. cyamopsidis are the main diseases of guar. Bacterial blight is seed-borne and infected seedlings are often killed rapidly. In older plants the disease develops from transparent, oily leaf spots coalescing into brown, angular, necrotic lesions. Infection spreads systemically throughout the plant and can kill it at any stage of development. The cultivars "Brooks", "Hall", and "Mills", which were originally resistant, are now affected by a highly virulent strain. Soaking the seed in hot water at 56 °C for 10 minutes will eliminate seed-borne infection. Alternaria leaf spot develops between flowering and pod set. It causes defoliation, especially during periods of high rainfall and humidity. Dithane and cupramar give excellent control of this disease. A mildew, caused by Oidiopsis taurica, is widespread and causes some damage, especially during periods of humid weather.
Guar is relatively free of pests. The midge Contarinia texana causes damage in the United States and has caused yield losses of 20-30%. Effective, economical chemical control is possible. A gall midge (Asphondilia sp.) occurs in India and the United States and may cause limited damage late in the growing season.
The best time for harvesting guar for fodder is during flowering and early pod formation. In India pods are often picked for home consumption before the fodder is harvested. In some regions guar is grazed, usually after frost, to reduce the risk of bloat in ruminants. It takes about 4-6 weeks from the onset of natural defoliation for guar to dry sufficiently to allow mechanical harvesting. The pods of most cultivars do not shatter. Moist conditions during this stage may cause the seed to weather and blacken. In India most harvesting is done manually and often starts when the stalks are still green. Subsequently, the plants are put in loose stacks, for rapid drying. This system avoids weathering of the seed, but harvesting too early will reduce the yield and the gum content. In the United States frost often kills the maturing crop, initiating rapid drying. Alternatively, desiccants such as paraquat may be used to promote drying. Harvesting is carried out with an adjusted standard combine harvester.
When grown for green pods, harvesting occurs 50-80 days after sowing, with the tender pods being picked every 2-3 days for several weeks.
As a rainfed forage or green manure crop, average yields in India are 8-12 t/ha, 10-12 weeks after sowing. Under irrigation, average yields are 16-20 t/ha. A green manure crop adds about 50 kg fixed nitrogen to the soil. Yield increments of crops following guar can be very high. Increases in wheat yield of 1500 kg/ha on light soils and 500 kg/ha on heavy soils are reported from India, while yield increases in cotton from 450-540 kg/ha are reported. In an experiment in the United States barley yield increased from 3.2 t/ha to 5.1 t/ha, 0.8 t/ha more than after other green manure crops.
Dry grain yield under rainfed conditions in India and the United States ranges from 350-1000 kg/ha, depending on rainfall and time of sowing. Under experimental conditions it rarely exceeds 1300 kg/ha. Yield can be more than doubled under irrigation. Under experimental conditions in the United States yields of over 3 t/ha have been obtained with "Kinman" and "Esser", in Zimbabwe over 3.5 t/ha with "Mills" and "Hall".
Average yield of green pods is about 2000 kg/ha for a premonsoon crop and 2500-3000 kg/ha for a monsoon crop. Experimentally, yields of over 9000 kg/ha have been obtained with "Pusa Mausami".
Handling after harvest
Guar gum is prepared from the seed by dry milling. In a multi-stage grinding and sifting process, the testa and cotyledons are removed to obtain "splits". Food-grade guar gum is made by grinding splits to a fine particle size. Most seed is milled to guar gum in the country of production.
Guar gum can be purified by autoclaving a mixture of the gum in water to obtain a 0.8% dispersion, followed by gradual addition of ethanol to a concentration of 40% and repeated centrifugation to precipitate the pure galactomannan.
The purified gum can be chemically changed to adjust its gel-making and water-binding characteristics to specific applications.
The National Bureau of Plant Genetic Resources, New Delhi, India and the Agricultural Research Institute, Lyallpur, Pakistan have representative collections of guar accessions. In the United States, the Texas Agricultural Experiment Station, Vernon, Texas and the Oklahoma State University, Stillwater, Oklahoma maintain collections. In addition to these actively used collections, the entire plant collection of 1300 accessions of 33 cultivars and local forms is stored at the National Seed Storage Laboratory, Fort Collins, Colorado.
Selection and breeding in guar in the United States aims at increased seed production and disease resistance, while in India cultivars have been selected for seed, vegetable, and multipurpose use. The American cultivars are derived from a very small number of introductions from India, leaving the genetic variability largely unutilized. An improved technique for controlled pollination of guar has been developed in India. Male sterility has been found, with pollen fertility probably being monogenically dominant over sterility.
Recent research has concentrated heavily on increasing grain yield. This was justified by the strong and growing market for guar gum and the increasing number of its applications. Development of determined cultivars with a compressed flowering phase and improved tolerance of temporary waterlogging have been suggested to increase its adaptability. Despite the crop's good prospects, research on guar all but stopped in the United States around 1985.
Although a few improved multipurpose cultivars have been developed in India, few efforts have been made to develop the green manure, cover crop, vegetable and forage aspects. These aspects would be most important in the drier parts of South-East Asia. There, it could become more important, being one of the few green manure and cover crops providing a useful by-product. Development of disease tolerance under humid conditions and agronomic research to incorporate it in a wider range of crop production systems would be urgently required.
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L.J. Wong & C. Parmar