Fagopyrum esculentum (PROSEA)
Fagopyrum esculentum Moench
- Protologue: Methodus pl.: 290 (1794).
- Family: Polygonaceae
- Chromosome number: 2n= 16
- Polygonum fagopyrum L. (1753),
- Fagopyrum vulgare Hill (1756, nom. illeg.),
- F. sagittatum Gilib. (1792, nom. illeg.).
- Buckwheat (En)
- Blé noir, sarrazin (Fr)
- Laos: khauz sa:m hlièmx
- Thailand: phakbung-som (northern)
- Vietnam: mạch ba góc, mạch hoa.
Origin and geographic distribution
Buckwheat is not an ancient crop. It was described for the first time in China in the 5th Century. It was probably domesticated in China from the shattering, wild species Fagopyrum acutatum (Lehm.) Mansf. ex K. Hammer (synonym: F. cymosum (Trevir.) Meissner), perennial buckwheat. For over a thousand years buckwheat has been an important subsistence and cash crop in the Himalayan area from northern India, Nepal, Burma (Myanmar), Mongolia and China to Korea and Japan. Although the total area may have declined, buckwheat is still very important in these areas. It is a popular food crop in some former Soviet Union republics. It is cultivated sporadically in the northernmost parts of South-East Asia, in northern Vietnam and northern Thailand. In the early Middle Ages it was introduced into Europe, probably through Siberia with the Mongols, to become a leading grain crop on poor soils and an important staple food. After its introduction by European emigrants, it became an important food crop in the United States and in Canada. It is occasionally cultivated elsewhere in the world. However, the increased use of chemical fertilizer in the beginning of the 20th Century led to the buckwheat area in Europe and North America decreasing enormously, to be replaced by higher yielding crops such as rye, oats, maize, wheat, and Irish potato. At present, it is regaining some importance in western countries because of its excellent nutritional qualities.
Buckwheat is commonly used for the preparation of noodles, pancakes, porridge, cakes and biscuits, comparable to those made from wheat. It is an ingredient in breakfast cereals. Groats is the part of the seed left after hulling. Buckwheat is often ground or milled coarsely, to produce broken groats. Many consumers like the coarsely milled flour (meal) which is brownish because of the high content of hull particles. At present, a high fibre content is considered a favourable character. When sieving for almost white buckwheat flour, the extraction rate is quite low, only 60-70%, the waste being used for fodder. Although pure buckwheat flour is sometimes used for baking bread, it lacks the gluten to provoke rising of the dough. It is popular for use in mixtures with wheat, barley or rye flour to improve the taste and nutritional value of bread and other foodstuffs. Up to 30% of buckwheat may be mixed in wheat dough for baking bread.
The tender shoots make a palatable green leaf vegetable. The flavonoid rutin, a traditional medicine, is present in all aboveground plant parts (leaves, stems, inflorescence, grain). Fresh leaves and inflorescences are used for industrial rutin extraction. In the Himalayas, buckwheat is processed into alcoholic drinks. In that area, people believe that buckwheat consumption reduces hazards of exposure to excessive solar radiation. Honeybees in buckwheat fields produce a dark coloured fragrant honey; a honey yield of 120 kg/ha may be attained. The grain is also fed to animals, especially pigs and chickens. The plants are occasionally used for silage, but must be mixed with other fodder because pure buckwheat silage may cause a cattle disease called fagopyrism. Buckwheat forms a good green manure. The seed hulls are used as litter in poultry houses, for stuffing pillows, as fuel or for compost.
Production and international trade
At present, buckwheat is still grown in many countries, and is mainly commercialized locally. Annual world production is about 1 million t from 2 million ha. The Russian Federation is the largest producer, followed by China (90 000 t), India (60 000 ha; 35 000 t), Canada, the United States, Brazil, Nepal, Japan (28 000 ha; 21 000 t). In Brazil, Canada, the United States and South Africa it is grown as an export crop in a highly mechanized way, like wheat. The farmgate prices are high, about double the price of wheat, but crops often fail, and average yields are low when compared with true cereals. Buckwheat noodles ("soba-uchi") are very popular in Japan, and the country imports 80% of its domestic demand, mostly from Brazil.
The seed has a cereal-like composition. The approximate composition of hulled buckwheat seed per 100 g edible portion is: water 10-15 g, protein 12-15 g, fat 2-3 g, carbohydrates 70-80 g, fibre 1.5 g, ash 1.5 g. Like small-seeded cereals, unhulled buckwheat grain is rich in fibre, containing up to 10%, the seed hull providing most of it. This may be partly or even almost completely sieved out from the flour. Stored flour may become rancid because of the high fat content. Buckwheat differs from true cereals in the high biological value of the protein, caused by the high content of essential amino acids, in particular lysine (6%). The high rutin content is also remarkable; it is about 1.2 mg per 100 g in boiled flour. Rutin is a vitamin that cures hypertension, reduces cholesterol count, protects the blood vessels from rupturing, and blood from forming clots. The flour is also rich in vitamins B1, B2and P. The straw has a reasonable good composition as a fodder, with 1.2% digestible protein, whereas buckwheat as green fodder contains about 2.9% digestible protein.
The 1000-kernel weight varies from 12-35 g, averaging about 22 g.
- Erect annual herb, 40-120 cm tall.
- Stem angular, hollow. Leaves alternate, upper ones almost sessile, lower ones with petiole up to 10 cm long; ocrea tubular, short, truncate; blade triangular, hastate or cordate, acute, 2-10 cm × 2-10 cm.
- Inflorescence compound, consisting of axillary or terminal clusters of flowers combined into corymbose pseudo-spikes.
- Flowers small, shortly pedicelled, rose-red to white; tepals 5, 3-4 mm long, persistent; stamens 8, alternating at the base with 8 honey glands; ovary 1-celled, trigonous, style tripartite with capitate stigmas; flowers show heterostylic dimorphy: some have 8 long stamens and 3 short styles, others have 8 short stamens and 3 long styles.
- Fruit a 3-sided achene or nutlet, 6 mm × 3 mm, sometimes winged, grey-brown, dark brown to almost black.
- Seed light green turning reddish-brown, slightly smaller than fruit.
Growth and development
At soil temperatures above 10 °C the seed germinates fast, and seedlings emerge after about 7 days. The crop grows fast, reaching the full height of 60-100 cm in 4-6 weeks. Growth is indeterminate. Flower formation starts 20 days after emergence, anthesis starts a week later and continues until complete senescence and death of the whole plant. After the onset of flowering, the vegetative organs (leaves and stems) continue to grow while the grain is forming, hence seed ripening is very uneven. From the middle of the flowering period onwards, when the leaf area has reached its maximum, further growth of vegetative organs is slow, and the seed has become the main sink for assimilates. Buckwheat is self-incompatible. Cross pollination occurs by insects, mostly bees and flies. The grain is ready for harvesting 70-130 days after emergence, depending on cultivar and ecological conditions.
Buckwheat has the reputation of producing an acceptable yield on marginal, infertile land, where other cereals or pseudo-cereals fail. On wet soils or soils rich in nitrogen, luxuriant growth leads to lodging, a low grain/straw ratio (down to 0.7), poor fruit setting, considerable losses during harvest, and thus modest yields. When used for silage or as green manure, a low grain yield is unimportant, and more biomass will be produced on wetter, heavier soils.
Other botanical information
The name "buckwheat" is the English translation of the genus name Fagopyrum which is derived from the latin word "fagus" (the beech or buck tree) and the greek word "pyron" (wheat). Its three-angled fruit resembles the beechnut.
Numerous landraces and cultivars are known in the main production areas, adapted to local ecological conditions, and with morphological and physiological differences, e.g. cultivars with well-filled roundish seed or very sharp-sided seed, cultivars for the summer or for the winter season, and special-purpose types for grain, fodder, vegetable or medicine.
A classification into 3 cultivar groups is possible, based mainly on the form of the fruit:
- cv. group Emarginatum (synonyms: Polygonum emarginatum Roth, Fagopyrum emarginatum (Roth) Moench, F. esculentum Moench var. emarginatum (Roth) Alef.); this is Japanese buckwheat with winged fruits, mainly cultivated in China, Japan and India;
- cv. group Esculentum (synonym: Fagopyrum esculentum Moench var. vulgare Alef.) with fruits triangular in cross-section;
- cv. group Pyramidatum (synonyms: Polygonum pyramidatum Loisel., Fagopyrum esculentum Moench var. pyramidatum (Loisel.) Meissner) with pyramidal fruits.
F. tataricum (L.) Gaertner is a related species, called tartary buckwheat or bitter buckwheat, grown in India and China under cooler and harsher conditions than normal buckwheat, and occurring as a weed in Europe. In Europe it used to be cultivated on the poorest soils, and used for feed or silage more than as cereal food. It produces more biomass for silage than normal buckwheat. It is distinguished from buckwheat by green flowers and dented seed sides. It is self-compatible, not heterostylic dimorphic and is assumed to have evolved from F. acutatum too. The wild perennial F. acutatum is said to be cultivated in Assam (India).
Buckwheat is a crop of temperate and subtropical areas, but may be grown successfully at higher elevations in the tropics. It is photosynthetically active between 10 °C and 40 °C, the optimum being between 15 °C and 25 °C. Exact data on optimal temperatures are scarce, but climate descriptions indicate a range of 18-30 °C for day temperatures, and night temperatures 5-10 °C lower. Because the leaf mass dries slowly, a dry period is required at maturity and harvest. Buckwheat is very sensitive to frost. Strong winds cause lodging during crop growth and shattering of the seed at maturity. The crop is rather sensitive to drought because of its poorly developed root system. During flowering, drought combined with high temperatures will cause poor seed setting. Much rain during the crop cycle stimulates vegetative growth, but inhibits seed setting, also because it hampers pollination by insects.
Buckwheat cultivars are either indifferent to daylength (day-neutral) or show a short-day photosensitivity. Typical autumn-cropping cultivars are short-day sensitive.
Buckwheat performs best on nitrogen-poor light sandy soils, from neutral to rather acid (pH value 4.5-7.0). It is suitable for newly cleared infertile land, drained marshland, rough land or acid soils with a high content of decomposing organic matter.
Propagation and planting
Buckwheat is propagated by seed. The seed has no dormancy. The seed-bed should be finely crumbed. A firm soil at about 5 cm depth reduces drought injury and lodging. Very crusted land and heavy clay soil will result in poor field emergence. Most growers use farm-saved seed. There are numerous landraces, but few improved cultivars are available. For seed production of improved cultivars the fields must be at least 200 m apart, because of the risk of outcrossing.
In mechanized cultivation, seed is drilled in rows about 30 cm apart, at a depth of 2-4 cm, requiring 40-60 kg of seed per ha, depending on seed quality, seed weight and density. The crop compensates for a thin stand by branching more. Thin stands produce more inflorescences and seeds per plant. In manual cultivation, seed is broadcast, followed by harrowing to cover the kernels with topsoil. Broadcasting requires 10-20 kg seed more per ha than row drilling. With a seed rate of 40 kg/ha and a 1000-seed weight of 20 g, about 200 seeds/m2 are sown, and with an establishment rate of 50%, a density of 100 plants/m2 will be obtained. A higher plant density has the advantage of better weed suppression, but the heavy leaf canopy may cause rotting of the inflorescence and lodging, and hampers harvest.
Buckwheat is a crop with a short growing season, easily fitting in cropping patterns with cereals, root crops, legumes, and forages. It is sometimes intercropped with vegetables.
No serious losses from soilborne diseases have been reported. Any crop is suitable as preceding crop provided that it does not leave much nitrogen or weed seeds. Although buckwheat competes well with most weeds, some fast-growing weeds are a problem. Some growers sow more densely on purpose, and then weed mechanically by harrowing about 4 weeks after emergence, killing most weed plants together with a number of buckwheat seedlings.
The uptake of minerals per ha for a yield of 2 t/ha grain is about 45 kg N, 10 kg P and 50 kg K. Growers usually apply no organic manure and no or little chemical fertilizer, e.g. 10-30 kg N, 0-15 kg P and 15-30 kg K. Only P and K fertilizers should be applied if there is a risk of lodging. Growers in western countries apply about 40 kg N, 15 kg P and 30 kg K, but recommendations for subtropical areas are lower: about 20 kg N, 15 kg P and 10 kg K. In some places, foliar application of the micronutrient boron has considerably increased the yield.
Diseases and pests
Although many fungal diseases have been reported on buckwheat, they only occasionally cause serious damage. The following diseases are to be noted: smut (Sphacelotheca fagopyri), leaf spot (Septoria polygonicola), root and basal rot (Phytophthora fagopyri), powdery mildew (Erysiphe polygoni), brown leaf spot (Ascochyta italica), rust (Puccinia fagopyri), root and collar rot (Sclerotinia libertiana), stem rot (Botrytis cinerea), root rot (Fusarium sp., Botrytis sp., Rhizoctonia sp.), chlorotic leaf spot (Alternaria alternata), stipple spot (Bipolaris sorokiniana), and downy mildew (Peronospora sp.). Cultivars differ markedly in susceptibility. Several viral diseases have been reported, but they do not cause much damage.
Bean weevil (Acanthoscelides obtectus), cutworm (Cirphis sp.), green peach aphid (Myzus persicae), grain moth (Cephitinea sp.) and storage beetles (Mycetophagus sp.) may cause some damage. Sometimes insecticide is sprayed, although it is doubtful whether this is economically justified.
The worst problem for buckwheat production is damage by birds at maturity and after harvest, when the crop is left to dry in the field. Rats are also sometimes destructive.
When most (at least 75%) seed is mature and most leaves have yellowed and dropped, the crop is harvested by mowing, after which the stems are bundled and put in heaps to dry. Farmers prefer to harvest early in the morning or late in the afternoon, or even at night, when the plants are slightly damp from dew, to reduce grain shattering. The bundles are stacked alternately head-to-tail in the heaps, to reduce bird damage. If the leaves are not dry enough, they may stick together, causing problems for threshing. Combine-harvesting is practised in more advanced countries.
A good crop yields about 2 t/ha of grain and 2.5 t/ha of straw. Grain yields normally vary from 0.6-2.5 t/ha, but 3.0 t/ha has been obtained from experimental plots in Korea. In Germany, average yields amount to 1.2 t/ha, in Japan to 750 kg/ha, and in India to 600 kg/ha. Buckwheat research has not succeeded in raising yields; they remain about the same as a century ago.
Handling after harvest
Thorough drying to a moisture content below 16% facilitates the removal of straw fragments and immature seed. Small farmers usually thresh manually, as in other small grain crops. Mechanical threshing requires careful regulation of the threshing cylinder to avoid damaging the seed. In Japan, standard quality grain should have less than 15% moisture, at least 85% healthy kernels, not more than 20% damaged or immature seed and no alien material.
Processing starts with hulling and separation of the hulls from the groats, followed by milling. Formerly, the grain was processed by individual households or in small village workshops. At present, most buckwheat is processed in factories that apply advanced food technology to make specific foodstuffs.
There are numerous landraces and many have already been collected for selection and testing, and for storage in genebanks. Germplasm is available in national collections in the United States, Canada, South Africa, Japan, Korea, China, India, Pakistan, Nepal, Russia, Slovenia, Poland, and Germany. These countries are part of a network under the International Plant Genetic Resources Institute (IPGRI), responsible for characterization and documentation. IPGRI plans to analyse and assess breeding and production constraints and to conserve genetic diversity for the Asia, Pacific and Oceania region.
Buckwheat has received relatively little attention from international and national research institutes. The important problems of the crop are lodging, seed shattering and low yields. These handicaps might partly be solved by improved cropping techniques and a proper breeding programme. Breeding has been carried out in, for example, the United States, Russia, Japan, India and former Yugoslavia. The mechanism of pollination and fertilization has been studied. Homomorphic, highly self-compatible diploid lines have been isolated. They revealed a severe inbreeding depression, and heterosis in F1generations. Breeders have selected improved cultivars with higher yields, e.g. by improving the plant habit. Autotetraploid buckwheat selections show superior characters in many aspects (self-fertile, higher rutin content, increased dry matter production, improved nitrogen uptake, no seed shedding). Tetraploid cultivars developed in Japan and China show a yield increase of about 20%.
Internationally, the interest in buckwheat as a health food is increasing. With a higher price compensating for the lower yield level compared to cereals, the acreage under buckwheat may increase. Buckwheat is fairly heat tolerant. It is potentially an interesting crop for marginal land in highland areas in South-East Asia, or as a winter crop in the northern part of the region, especially as a low-input subsistence or cash crop in rotation with other crops. An interesting feature is that at the moment buckwheat is hardly affected by diseases and pests. Giving the existing genetic variability, it is likely that breeding will result in cultivars better adapted to more tropical conditions, with less lodging and seed shattering, and improved seedset, hence with higher yield levels.
The International Buckwheat Research Association (IBRA) issues a newsletter "Fagopyrum" and organizes international meetings.
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