Hordeum vulgare (PROSEA)
- Protologue: Sp. pl.: 84 (1753).
- Family: Gramineae
- Chromosome number: 2n= 2x= 14
- Hordeum distichon L. (1753),
- H. hexastichon L. (1753),
- H. sativum Jessen (1863).
- Barley (En)
- Orge (Fr)
- Cebada (Sp)
- Malaysia: barli. Indo-China: ta mé (Chinese), tai mak (Cantonese)
- Thailand: khao-ba-le
- Vietnam: lúa mạch, lúa mạch nha, dại mạch.
Origin and geographic distribution
Barley was domesticated in the Fertile Crescent of the Middle East from wild barley populations (sometimes considered as a separate species H. spontaneum C. Koch) before 7000 BC. It was the most abundant and cheapest grain of the ancient Near East. It spread over the Old World between 5000-2000 BC, reaching India 3000 BC and China in 2000 BC; it was taken to the New World by Columbus. At present it is grown over a broader environmental range than any other cereal, from 70 °N in Norway to 44 °S in New Zealand. In Tibet, Ethiopia and the Andes it is cultivated higher on the mountain slopes than other cereals. In many areas of northern Africa, the Near East, Afghanistan, Pakistan, Eritrea, and Yemen it is often the only possible rainfed crop. In South-East Asia it is grown to a limited extent in central Burma (Myanmar), Thailand and, very rarely, in Indonesia in the mountainous areas of East Java.
In the tropics and subtropics barley is cultivated for food, e.g. in India, Nepal, Tibet, Afghanistan, Russia, Ethiopia, North Africa, and the Andean region of South America.
The straw is used as animal feed in the Near East, northern Africa, Ethiopia, Eritrea, Yemen, in the Andes and the Far East; it is also used for animal bedding and to cover roofs. Barley is often grazed during tillering or cut before maturity and fed directly to livestock or used for silage.
In temperate regions, the crop is used as feed and for the production of malt to prepare beer; the brewing process varies with the type of beer being produced.
Production and international trade
In 1993, world barley grain production was about 170 million t from 74 million ha. Major producing countries are Russia (26 million t), Germany (13 million t) and Canada (12 million t). Over 60% of the world production is in Europe. The main producing countries in East Asia are China (3.1 million t, 1.2 million ha) and India (2.5 million ha). In South-East Asia, Thailand produced 1400 t from 2000 ha. World production is about 36% of that of maize and 30% of that of wheat. Europe, Canada and the United States are the largest exporters. The largest importers in South-East Asia are Thailand, the Philippines, Malaysia, Papua New Guinea and Indonesia.
Barley grain contains approximately per 100 g edible portion: water 13 g, protein 12 g, fat 2 g, carbohydrates 68 g, fibre 3.5 g, ash 1.5 g. Hordeins are the major storage proteins in the endosperm and have a low lysine content. The major constituent of the kernel is starch, which consists of a mixture of amylopectin (about 75%) and amylose (about 25%). The fat content in barley is low compared to that of maize. The grain is an excellent source of vitamins of the B-complex (B1, B2, B6) and panthotenic acid. Barley cannot be used to make leavened bread because of its low gluten content. The 1000-kernel weight is 25-50 g.
- Annual, erect grass, 80-120 cm tall, tillering freely.
- Root system consisting of 3-9 primary (seminal) roots and of adventitious (nodal) roots; only seminal roots develop under severe drought.
- Stem usually hairy, with solid nodes and 5-7 hollow internodes.
- Leaves 5-10, borne alternately on either side of the stem at the nodes; sheath glabrous; auricles overlapping and much larger than in wheat or rye; ligule membranaceous, 1-3 mm long, hyaline, ciliolate; blade linear-lanceolate, 5-40 cm × 0.5-1.5 cm, scaberulous.
- Inflorescence a terminal cylindrical spike, 5-12 cm long, excluding the awns; rachis non-disarticulating, with 1-flowered spikelets alternating in distichous groups of 3 at each node; in 2-rowed barley, only the central spikelet of each group is fertile (hetero-spiculate barley), in 6-rowed barley, the lateral spikelets are also fertile (iso-spiculate barley); glumes 2, narrow, about half the length of the lemma, with fine bristles at the tip; lemma ovate, 9-11 mm × 3 mm, 5-nerved, usually terminated by a long barbed awn up to 15 cm long, but some cultivars are awnless; palea 2-keeled, as long as the lemma but awnless; floret with 2 lodicules, 3 stamens and ovary with 2 plumose stigmas.
- Fruit a caryopsis, 20-60 per spike, elliptical in frontal view, convex on the embryo side, varying in size according to cultivar, hairy at the tip, grooved on the hilum side, usually invested by lemma and palea but "naked" forms, in which the husks do not adhere to the grain, occur as well.
Growth and development
The coleoptile emerges from the soil 5-6 days after germination. Tillers are produced on the main shoot and the process continues until flower initiation. Time to flower initiation varies with cultivar, but barley flowers earlier than wheat. Barley is predominantly self-pollinating but cross pollination can be as high as 10%. It can mature in a short season of 3-4 months.
Other botanical information
The large variability in barley led to many "species" being distinguished in the past. At present, the most accepted view is that in barley evolution only a single species is involved, H. vulgare, forming a crop-weed complex, in which the cultivated barleys have been developed from original wild populations and the modern cultivars are the result of breeding and selection. "Hybrids" between wild and cultivated forms are easily obtained and are fully fertile. In wild forms (formerly classified as H. spontaneum C. Koch) the spikes are 2-rowed and fragment at maturity, and the grains fall. In domesticated forms 6-rowed spikes were developed as well as 2-rowed ones, and the spikes are tough and the grains do not fall. Crossings of barley with other Hordeum species result in sterile hybrids. No other species are known to be involved in barley evolution.
Hundreds of barley cultivars exist; they have been grouped into 3 cultivar groups (there is no generally accepted classification system):
- cv. group Vulgare, including iso-spiculate, 6-rowed, tough-rachis barley cultivars, which again can be grouped into several cv. subgroups based on lemma characteristics (long-awned, hooded or awnless);
- cv. group Distichon, including hetero-spiculate, 2-rowed, tough-rachis cultivars, which can also be grouped into several cv. subgroups based on characteristics of the spikes (normal, compressed and flabellate, or bearing spikelets with much reduced parts);
- cv. group Irregulare, including cultivars in which the spikes are composed of an irregular mixture of iso-spiculate and hetero-spiculate spikelets.
Based on vernalization requirements, barley can also be classified as winter or spring barley.
Barley can grow at low temperatures during its vegetative phase, but can endure high temperatures during and after heading, provided the relative humidity is low. In temperate countries it can be grown as a winter or as a spring crop, just like wheat. In India, it is planted in October-November at the close of the monsoon. In Kenya, it grows in areas of light rainfall between 1500-3000 m altitude.
Barley is best adapted to temperate climates with cool and moderately dry seasons. The crop withstands high temperatures in dry climates, but is ill-adapted to hot, humid climates. It is adapted to areas with annual rainfall ranging from 200 mm to more than 1000 mm; it is very sensitive to waterlogging, but very drought tolerant. It is less cold tolerant than wheat or rye. Barley does not tolerate acid soils, but is more salt tolerant than other cereals.
Propagation and planting
Barley is propagated by direct seeding. On smallholdings the land is prepared by animal traction. The depth of ploughing is 10-15 cm. Preferably, the seed should be treated with a fungicide to protect the crop against seed and soilborne diseases. On smallholdings and in adverse environments sowing is done by hand; normally, the seed is drilled 2-6 cm deep in rows 15-35 cm apart. Seeding rate is 50-150 kg/ha. Average plant density is 200-250 plants/m2.
Weeding is essential to procure a reasonable yield. Resource-poor farmers weed manually and use the weeds as animal feed. Post-emergence spraying of 2,4-D is widely used to control broad-leaved weeds. Barley requires about 25 kg/ha of nitrogen to produce 1 t of grain. Nitrogen can be applied before sowing or by top dressing after germination. Under dry conditions high rates of N-application can reduce yields, whereas under favourable conditions high rates of nitrogen increase the occurrence of lodging and diseases. N-fertilization of malting barley may increase the protein level in the grain above the permitted level. As a barley crop removes 15-20 kg/ha of phosphorus, this amount should be applied to maintain soil reserves.
Diseases and pests
Barley is affected by several viral and fungal diseases. The most important viral diseases are barley yellow dwarf virus (BYDV) and barley stripe mosaic virus (BSMV). Major fungal diseases are powdery mildew (Erysiphe graminis), spot blotch (Helminthosporium sativum), scald (Rhynchosporium secalis), scab (Giberella zeae), rusts (Puccinia spp.), net blotch (Pyrenophora teres), barley stripe (Helminthosporium gramineum), and smuts (Ustilago spp.). Several nematodes can parasitize barley: e.g. root-knot nematode (Meloidogyne sp.), cyst nematode (Heterodera sp.) and root-lesion nematode (Pratylenchus sp.).
Major pests are aphids.
Barley can be harvested when the grains reach 35% moisture content. It is harvested by hand or by combine. Hand-harvesting is done by sickle or by pulling the plants. Special care must be taken when threshing malting or naked barley, to minimize the amount of broken seed.
Barley yields vary from 0.3 t/ha in dry years and under marginal conditions to 10 t/ha in high-input agriculture. Average yields vary from 1.5-1.7 t/ha in Asia and South America to 2.9 t/ha in North America and 4 t/ha in Europe. Straw yields are equally important in many developing countries but no data are available.
Handling after harvest
The major problem for harvested grain is damage and losses caused by insects and rodents. A high moisture content at harvest favours the development of mycotoxins dangerous to humans and certain animals (e.g. cattle, pigs, poultry). In developing countries it is common practice to keep selected spikes to produce the seed for the next cropping season. Barley seeds having 14% moisture content can be safely stored.
For the brewing of beer, 2-rowed barleys with a low protein content, a soft mealy endosperm and a thin hull are preferred. The grain is germinated and when the radicle appears the very young seedlings are dried to produce malt. The malt is mixed with water and heated; the malt enzyme diastase hydrolyses the starch to fermentable maltose and glucose and the bitter flavour is imparted by boiling with the flower buds of hops (Humulus lupulus L.). The resulting wort is then cooled and fermented by brewers' yeast (Saccharomyces cerevisiae), which produces alcohol (3-8%), carbon dioxide and flavouring substances. The yeast is removed by settling and filtration; further carbonation is usually provided before the beer is bottled or canned.
The primary centre of diversity for barley is the Fertile Crescent in the Middle East, with Ethiopia being an important centre of diversity. The International Centre for Agricultural Research in the Dry Areas (ICARDA, Syria) plays a major role in collecting, maintaining and distributing barley germplasm. The Centre collaborates with several national programmes in collecting and evaluating germplasm. Many national programmes maintain their own working collections.
Landraces are still cultivated today in many countries and are composed of many different homozygotes. These landraces are maintained by the farmers themselves. Before 1950, the main breeding method was either mass selection or pure-line selection within landraces. New variability has been created by crossing or by mutation. ICARDA has the mandate for barley improvement in developing countries. The major emphasis is on producing cultivars resistant to diseases and pests and with adaptation to specific agro-ecological environments. Ethiopian barleys often show good disease resistance.
Barley has received less attention in crop improvement than wheat, rice and maize. As breeding has mostly addressed favourable environments, the potential of the crop in low-input agriculture is largely underexploited. Considerable improvement is expected in breeding cultivars resistant to lodging and diseases. However, since barley is primarily a cereal for temperate climates, it will most probably remain unimportant in South-East Asia.
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