Prota 1: Cereals and pulses/Céréales et légumes secs
Sp. pl. 2: 730 (1753).
Papilionaceae (Leguminosae - Papilionoideae, Fabaceae)
2n = 14
Grass pea, chickling pea, chickling vetch, white pea (En). Gesse, gesse blanche, gesse commune, pois carré, lentille d’Espagne (Fr). Chícharo, chícharo comun, sincho (Po).
Origin and geographic distribution
The origin of Lathyrus sativus is unknown. Records exist of wild Lathyrus sativus plants in Iraq, but it is not clear if these are truly wild or escapes from cultivation. Lathyrus sativus is perhaps a derivative from Lathyrus cicera L., which occurs wild in southern Europe, northern Africa and western Asia and is sometimes grown there. Domestication of grass pea probably took place in the Balkan around 6000 BC. Remains of Lathyrus sativus dating back to 2000–1500 BC have been recorded from India. Nowadays grass pea is widely cultivated in large parts of Asia (especially Bangladesh, India, Nepal, Pakistan and the Middle East), southern Europe and northern Africa, and to a lesser extent in America, Australia and South Africa. In tropical Africa it is mainly grown in Ethiopia, but also in Sudan, Eritrea, Kenya, Tanzania, Angola and Mauritius.
In Ethiopia and Eritrea grass pea seeds are mainly consumed in the form of sauces (‘wot’); ‘shiro wot’ (sauce made of flour) and ‘kik wot’ (sauce made of hulled split seeds) are eaten together with ‘injera’ (a pancake-like unleavened bread). Boiled grass pea seeds (‘nifro’) are also consumed in most areas, whereas ‘kitta’ (an unleavened bread) made from grass pea seeds is consumed mainly during times of acute food shortage. In India the seeds are sometimes boiled whole, but are most often processed into dhal. The flour, made by grinding either the whole or split seeds, is sold as ‘besan’. In Bangladesh ‘roti’ made out of grass pea flour is a staple for landless labourers. In India grass pea is sometimes used to adulterate more expensive pulses, such as chickpea or pigeon pea. Care should be taken in the consumption of grass pea seeds, as excessive consumption leads to a neurological disorder in people and animals, called lathyrism and characterized by paralysis of the lower limbs. In many countries grass pea seeds are used as animal feed, e.g. as an ingredient in pig starter and grower diets.
In Asia immature pods are cooked and eaten as a vegetable, or are boiled, salted and consumed as a snack. Young vegetative parts are cooked as a green vegetable; they are also dried for off-season use as a vegetable. Young grass pea plants are used as fodder for cattle or for grazing in many countries. The stems and chaff remaining after harvest are often the most important reason for growing the crop in Asia. As fodder, the plants can be eaten green or as hay; they are not suitable for silage. Grass pea is grown as a green manure, e.g. in Australia and Canada. Oil from the seeds is used medicinally as a powerful cathartic.
Production and international trade
According to estimates India produced about 0.8 million t grass pea seeds per year from 1.5 million ha in the mid 1990s, whereas production was lower in Bangladesh (175,000 t from 240,000 ha) and Pakistan (45,000 t from 130,000 ha). In the late 1990s production in Ethiopia was estimated at 105,000 t from 142,000 ha. As a food grain, grass pea is traditionally traded within the region of production, and it does not enter international trade.
The composition of whole grass pea seed per 100 g edible portion is: water 8.4 g, energy 1457 kJ (348 kcal), protein 27.4 g, fat 1.1 g, carbohydrate 59.8 g, fibre 7.3 g, Ca 127 mg, P 410 mg and Fe 10.0 mg (Leung, Busson & Jardin, 1968). Grass pea is highly deficient in methionine and tryptophan. Raw whole seeds contain 41% starch on a dry matter basis; the starch granules are oval and on average 25 μm long and 17 μm wide.
The neurological disorder lathyrism is caused by the water-soluble non-protein amino acid ODAP (β-N-oxalyl-L-α,β-diaminopropionic acid), also known as BOAA (β- N-oxalylamino-L-alanine) and OAP (L-3-oxalylamino-2-aminopropionic acid). ODAP is present in all parts of the plant and affects various parts of the central nervous system, disrupting neurotransmission and thus impairing muscular activity. The onset of lathyrism can be slow or sudden, and is often indicated by a feeling of heaviness and pain in the lower limbs. Lathyrism is often irreversible, but not fatal. Lathyrism seems to occur when food ratios containing at least 25% grass pea are consumed continuously over 1.5–6 months and may then affect up to 5% of the population. Outbreaks of lathyrism often occur during near-famine conditions that force people to rely too heavily on grass pea. The ODAP content of grass pea seeds typically ranges from 0.1–1.4(–2.5) g per 100 g seed. ODAP levels are not only genetically determined, but also highly influenced by growing conditions. In general, soaking and boiling reduce ODAP levels in the seeds, and this effect is enhanced if water is changed after soaking and during cooking. When the seeds are ground into flour, which is then used in baking or cooking, ODAP may not be removed. Unfortunately, effective detoxification treatments often also result in decrease of nutritional quality. Other antinutritional factors in grass pea include trypsin inhibitors, tannins, lectins, phytate and oligosaccharides.
Grass pea hay contains: water 14.6%, protein 9.9%, fat 1.9%, fibre 36.5%, nitrogen-free extract 31.0% and ash 6.1%. The seeds of cultivars with up to 0.22 g ODAP per 100 g seed could be included in the diets of growing chicks at a rate of 400 g grass pea seeds per kg feed without negative effects on weight gain or fat or protein digestibility.
Much-branched, erect, straggling or climbing, glabrous annual herb; stem slender, quadrangular, winged, up to 90(–170) cm long; taproot well-developed. Leaves alternate, 2- or 4-foliolate, ending in a simple or branched tendril; stipules prominent, leaf-like, narrowly triangular, with a smaller but similarly shaped basal appendage and often with a small tooth between the lobes; petiole mostly winged, (1–)1.5–2.5(–3.5) cm long; leaflets sessile, narrowly elliptical-oblong, (3–)4–5(–7.5) cm × 3–5(–13) mm, cuneate at base, acute or acuminate at apex. Flowers solitary in leaf axils, bisexual, papilionaceous, pedicel with joint, lower part (1–)3–3.5 (–5) cm long, upper part (2–)5–7(–8) mm long; calyx campanulate, tube c. 3 mm long, lobes 5, almost equal, narrowly triangular, 3–6 mm long; corolla blue, reddish-purple, red, pink or white, standard erect and spreading, very broadly obovate, c. 15 mm × 18 mm, clawed, retuse at top, wings broadly obovate, c. 14 mm × 8 mm, clawed, with auricle, keel slightly twisted, boat-shaped, c. 10 mm × 7 mm, clawed, with 2 auricles; stamens 10, 9 united and 1 free; ovary superior, sessile, c. 6 mm long, style abruptly upturned, c. 7 mm long, stigma spoon-shaped. Fruit an oblong, flattened pod (1.5–)2.5–4.5(–5.5) cm × 0.5–2 cm, upper margin 2-winged, shortly beaked, glabrous, (1–)2–5(–7)-seeded. Seeds wedge-shaped, 4–7 mm in diameter, white, pale green, grey or brown, marbled; hilum elliptical. Seedling with hypogeal germination.
Other botanical information
Lathyrus comprises about 150 species, mainly in the temperate regions of the northern hemisphere and South America, with a few species in Africa. Lathyrus sativus is placed in section Lathyrus along with about 30 other annual or perennial species. Based on crossability and cytological evidence, Lathyrus amphicarpos Gouan and Lathyrus cicera L. have been placed in the secondary gene pool of grass pea. More recently, successful crosses between Lathyrus sativus and Lathyrus pseudocicera Pamp. have been made. Apart from Lathyrus sativus, other Lathyrus species cultivated in Ethiopia are the ornamental Lathyrus odoratus L. and the forage Lathyrus aphaca L.
Infraspecific classification is mainly based on colour of flowers, markings on pods and size and colour of seeds. In general, white seed is most popular for human consumption. The level of infraspecific variation for RAPD markers is low compared to other grain legumes such as lentil and pea. Based on isozyme analysis variation was found to be highest in western Asia and northern Africa.
Growth and development
Germination of grass pea seeds is most rapid around 20°C. Flowering time is 1.5–4 months after sowing. The floral biology of grass pea favours self-pollination (anthers usually dehisce before full opening of the flower), but there are many records of substantial outcrossing (up to 28%). Total crop duration is 3–6 months. Grass pea effectively nodulates with Rhizobium leguminosarum.
Grass pea is grown successfully in regions with an average annual rainfall of 400–650 mm/year and an average temperature of 10–25°C. It withstands heavy rains in early growth stages and prolonged drought during grain-filling. It grows well in the subtropics as a winter crop. Grass pea can be grown on a wide range of soil types, including poor soils and heavy clays. It tolerates waterlogging and moderate salinity. In Ethiopia grass pea is often grown in the dry season on residual soil moisture in heavy black clay soils at 1700–2700 m altitude. In India grass pea is grown as a cold-season crop up to 1200 m altitude.
Propagation and planting
Grass pea is propagated by seed. The 1000-seed weight ranges from 30–300 g. In Ethiopia it does not require a fine seedbed; 1–2 ploughings are enough. The average seed rate is normally 45–60 kg/ha for a sole crop, and about 35 kg/ha when intercropped. Seeds that may have been soaked in water overnight are broadcast or drilled in furrows. Plant densities of 200,000–250,000 plants/ha are common for grass pea. In Ethiopia grass pea is usually sown in September–November and harvested in January–April.
Grass pea is grown as a sole crop or intercropped, e.g. with barley, linseed or chickpea. In many countries grass pea is produced in rice-based cropping systems before the rice crop or alternately with a rice crop. In India grass pea is often grown as a relay crop: it is broadcast into a standing rice crop about 2 weeks before the rice harvest and left to grow on the residual moisture.
Grass pea often receives hardly any attention after sowing, although for optimum yields it should be kept reasonably free from weeds. In a well-prepared field, the crop comes up as a thick mass over the entire surface, smothering out weeds. Grass pea is not normally fertilized, but atmospheric nitrogen fixation rates of 25–50 kg/ha have been recorded. In Ethiopia grass pea is grown in rotation after barley or sometimes after a pulse crop, such as pea or chickpea, which has been sown in April and harvested in July.
Diseases and pests
The main diseases of grass pea are powdery mildew (Erysiphe pisi) and downy mildew (Peronospora spp.), but the latter not in Ethiopia. Rust (Uromyces fabae) and Fusarium wilt (Fusarium oxysporum) have been recorded from Ethiopia. Faba bean necrotic yellows virus (FBNYV) has been observed on grass pea in Ethiopia; it is transmitted by the aphids Acyrtosiphon pisum and Aphis craccivora. In host-range studies grass pea was found to be susceptible to pea seed-borne mosaic virus (PSbMV). Insect pests of grass pea include aphids and thrips. The pea aphid (Acyrthosiphon pisum) is the main pest of grass pea in Ethiopia.
Harvesting of grass pea should be done when leaves turn yellow and pods turn grey, to avoid shattering. The plants are pulled out by hand or cut with a sickle near the base. They are then stacked and allowed to dry for 7–8 days in the field or on the threshing floor.
The average seed yield of grass pea is 350–700 kg/ha; in Ethiopia it is about 700 kg/ha. Yield trials conducted recently in various countries recorded yield levels of 1500–3000 kg/ha.
Handling after harvest
Grass pea pods are threshed by animal trampling or by beating with sticks, after which the seed is winnowed and cleaned. The seeds may be dried for a few days before storage.
ICARDA (Aleppo, Syria) holds a Lathyrus collection of about 1880 accessions, of which 1560 belong to Lathyrus sativus. Large grass pea germplasm collections are also kept in France (IBEAS, Laboratoire d’Ecologie Moleculaire, Université de Pau; 1810 accessions), Australia (Australian Temperate Field Crops Collection, Horsham, Victoria; 844 accessions), Russia (N.I. Vavilov All-Russian Scientific Research Institute of Plant Industry, St. Petersburg; 688 accessions), Bangladesh (Plant Genetic Resources Centre, Bangladesh Agricultural Research Institute (BARI), Joydebpur, Gazipur; 584 accessions) and the United States (USDA/ARS Western Regional Plant Introduction Station, Pullman, Washington; 248 accessions). In tropical Africa germplasm collections are kept in Ethiopia (197 accessions at the Institute of Biodiversity Conservation, Addis Ababa; 13 accessions at the International Livestock Research Institute (ILRI), Addis Ababa) and Kenya (National Genebank of Kenya, Crop Plant Genetic Resources Centre, KARI, Kikuyu; 4 accessions). Grass pea seeds show orthodox seed storage behaviour.
The major objective in grass pea breeding is reduction of ODAP levels, which is the most feasible method of producing a safe crop. Secondly, increasing the genetic yield potential is an important goal. Other breeding objectives are the incorporation of disease resistance and increase of seed size, earlier maturity and a higher harvest index. Lines with moderate resistance to powdery mildew have been identified. In Ethiopia a large number of accessions and breeding lines introduced from ICARDA are resistant to powdery mildew.
Improvement has been slow in grass pea. High-yielding improved cultivars low in ODAP and with resistance against biotic and abiotic stresses have not been released in Africa. Some attempts to provide improved cultivars with low ODAP content have been made in India. In Chile and Bangladesh some promising lines have also been identified with low ODAP and high yield. Recently, of the 13 lines with low ODAP content identified in Ethiopia, three lines introduced from ICARDA have consistently shown low ODAP and reasonable yield over three years. However, the substantial outcrossing rate in grass pea has limited the progress in identifying stable lines with low ODAP content; seeds of selected lines must be multiplied in isolation and be provided to farmers every year.
Indirect somatic embryogenesis (from callus) is possible in grass pea using shoot tips, axillary buds, and stem, leaf and root explants. Direct somatic embryogenesis has been achieved from immature leaflets and nodal segments. Somaclones with low ODAP combined with high yield have been developed. Other biotechnological approaches applied in breeding for low ODAP grass pea types include incorporation into grass pea of ODAP-degrading genes from microbes, and application of antisense technology to silence the genes involved in the bio-synthesis of ODAP. Transgenic grass pea plants have been produced using bombardment of explants with DNA-coated particles. Genetic linkage maps of the Lathyrus sativus genome have been developed using various molecular markers (RAPD, STMS and STS/CAPS), and quantitative trait loci associated with resistance to ascochyta blight (Mycosphaerella pinodes) have been located for possible future transfer of this trait into the closely related Pisum sativum L.
Grass pea is the least preferred among the common food legumes, but it has a number of features that make it attractive particularly to resource-poor farmers, because of its adaptation to harsh conditions such as drought and waterlogging. Therefore, grass pea is a useful crop for dry and poor soils and a rescue crop when other crops have failed. However, the presence in the seeds of the toxin ODAP is a serious disadvantage, as it poses a real danger to the health of consumers. Cultivation of grass pea is often discouraged or has sometimes even been forbidden, e.g. in certain states of India, but this has not been successful due to the absence of cheap alternatives. The first priority in grass pea breeding therefore is the development of high-yielding cultivars with low ODAP content, which can safely be consumed. Also, more research is needed on effective detoxification methods without reducing the nutritional value of the seeds.
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Sources of illustration
• Jansen, P.C.M., 1989. Lathyrus sativus L. In: van der Maesen, L.J.G. & Somaatmadja, S. (Editors). Plant Resources of South-East Asia No 1. Pulses. Pudoc, Wageningen, Netherlands. pp. 50–51.
Correct citation of this article:
Yadav, S.S. & Bejiga, G., 2006. Lathyrus sativus L. In: Brink, M. & Belay, G. (Editors). PROTA 1: Cereals and pulses/Céréales et légumes secs. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, flowering and fruiting branch; 2, seeds.
flower and fruits
field with ripening crop