Triticum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Triticum L.

Protologue: Sp. pl.: 85 (1753); Gen. pl. ed. 5: 37 (1754).

Family: Gramineae

Chromosome number: x= 7; 2n= 6x= 42 (T. aestivum); 2n= 4x= 28 (T. turgidum)

Major species and synonyms

• Triticum aestivum L., Sp. pl.: 85 (1753). Synonyms: T. sativum Lamk (1779, excl. T. turgidum L.), T. vulgare Vill. (1787), T. cereale Schrank (1789).

• Triticum turgidum L., Sp. pl.: 86 (1753). Synonyms: T. durum Desf. (1798), T. dicoccum Schübler (1818), T. dicoccoides Körn. ex Schweinf. (1908).

Vernacular names

General:

• Wheat (En, Am)
• Blé (Fr)
• Indonesia: gandum
• Malaysia: gandum
• Philippines: trigo
• Thailand: khao-sa-le, sa-le
• Vietnam: lúa mì, lúa miền.

T. aestivum:

• Bread wheat, common wheat (En, Am)
• Blé tendre (Fr).

T. turgidum:

• Durum wheat, emmer wheat, macaroni wheat (En, Am)
• Blé dur (Fr).

Origin and geographic distribution

Early wheats were first domesticated between 7500 and 6500 BC in the Fertile Crescent region of the Middle East. Wheat was cultivated in ancient Greece, Persia, Egypt, and throughout Europe in prehistoric times. It was an important crop in South-West Asia when history was first recorded. By the third millennium BC, the crop had reached China. In 1529, the Spanish introduced wheat to the New World. It was first cultivated in the Philippines in 1664. Of all the cereals, wheat is the most widely adapted, being grown from sea-level to altitudes of more than 4500 m, and from the equator to within the Arctic Circle. About 90% of the area under the cultivated wheats is planted to bread wheat and 10% to durum wheat. Wheat is not widely grown within South-East Asia, but pockets of wheat are cultivated in most countries.

Uses

Wheat provides almost 20% of all human food energy. It is made into various products including bread (leavened, flat and steamed), chupatties, pastries, crackers, biscuits, pretzels, noodles, farina, macaroni, spaghetti, bulgur, couscous, breakfast foods, baby foods, and food thickeners. It is also used as a brewing ingredient in certain beverages.

In South-East Asia, wheat utilization has been adapted to the local cuisine. For example, in Thailand, whole wheat may be boiled and added to rice and curries, fried with vegetables, and used for desserts; cracked wheat is added to boiled porridge with vegetables and pork, to chilli paste that is eaten with rice, to "tabooleh" salad with chillies, and to desserts with coconut milk; wholemeal flour is used to make noodles and baked or steamed breads, and as gluten for meat substitutes. In the Philippines, "pandesal" (breakfast bread) is a sought after specialty. In most of South-East Asia, wheat products are in transition from a luxury to a staple food. In many Asian countries, wheat flour is mixed with substitute components (5-30%), such as starch from maize, rice, and cassava, to produce bakery products of acceptable appearance, flavour and nutritional quality.

Byproducts of flour milling, particularly the bran, are used almost entirely to feed livestock, poultry or prawns. Because of its relatively high content of protein (25%), and vitamins (B-complex and E), wheat germ (from wheat embryos) is sold as a human food supplement.

Industrial uses of wheat products centre on the production of glues, alcohol, oil and gluten. Straw is fed to ruminants or used for bedding material, thatching, wickerwork, newsprint, cardboard, packing material, fuel and as substrate for mushroom production.

Production and international trade

In 1992, world wheat production was 567 million t, produced on 220 million hectares. Major producers are the United States, Canada, Russia and China. Developing countries were responsible for 35% of global wheat production. In South and East Asia, China, India, and Pakistan are the principal producers. During the 1990-1992 crop years, Burma (Myanmar) devoted 130 000-140 000 ha to wheat production. Small areas of wheat have been grown in rotation with rice or other local crops for many centuries in the highlands of Java (Indonesia), the northern highlands of Luzon (the Philippines), the northern mountains of the Cao Bang, Son La, and Lai Chau Provinces of Vietnam, and in the northern highlands of Thailand. Areas have never exceeded 2000 ha in any of these countries. During the Spanish occupation of the Philippines, some wheat was exported through the galleon trade from Manila to Acapulco (Mexico).

All countries in South-East Asia import wheat, totalling 6.6 million t annually in 1991-1993. Indonesia imported the largest share (2.5 million t), followed by the Philippines (1.8 million t), Malaysia (1.1 million t), Thailand (0.6 million t), Vietnam (0.3 million t), and Singapore (0.2 million t). The world price of wheat has fluctuated between US$ 110-210 per t over the last 10 years.

Average per capita wheat consumption in South-East Asia is 14 kg/year, and is growing at a rate of 4.8% per year. The global annual per capita consumption is 106 kg. Imports have caused financial strain in these countries, which has provided an incentive to promote domestic production.

Properties

The composition of a wheat grain (caryopsis) is 7-8% of coat material, 90% endosperm and 2-3% embryo. The embryo mainly comprises oil and protein, and little starch. The endosperm is starchy, and is surrounded by the aleurone layer which is rich in proteins. When a wheat grain is milled, the outer layers and embryo are separated from the endosperm. The pulverized endosperm becomes the wheat flour, while the other parts form the bran.

The endosperm varies both in hardness and vitreousness: hard bread wheats high in gluten protein tend to be vitreous and lowprotein soft wheats tend to be opaque. Hard wheats are best suited for bread making while the soft wheats are best for biscuits and pastries. Flour colour varies from white to slightly yellow.

Grain protein content for bread-making purposes must be 11-15%. More gluten-type proteins increase the strength of the dough produced, allowing the expanding loaf to retain its shape during baking. Loaf volume is one of the most important final quality criteria. Protein levels may be less than 10% for biscuits, cakes and pastries. Chupatties, arabian breads, steamed bread, and noodles require intermediate quality characteristics. Durum wheat is used to make pasta products. The grain is vitreous, amber in colour, and is much harder than bread wheat. The coarse flour (semolina) is used to make spaghetti, macaroni, certain noodles, etc. Gluten strength tends to be low. Protein should have a minimum level of 12%, and the grain must contain a high amount ofβcarotene, which imparts the desired yellow colour.

Wheat contains high levels of energyproducing carbohydrates. The energy value of wheat is 1300-1500 kJ/100 g. The constituents of the whole grain per 100 g are: water 11-14 g, protein 8-16 g, fat 1.7-4.0 g, carbohydrates 69-72 g, fibre 2-3 g, and ash 1.5-1.8 g. Constituents of white flour are per 100 g: water 12.0-12.4 g, protein 10-12 g, fat 1-1.2 g, carbohydrates 74-76 g, fibre 0.3-0.4 g, and ash 0.3-0.5 g. Wheat is deficient in the amino acids lysine and threonine, and somewhat in isoleucine and valine. It is a good source of Bgroup vitamins and minerals.

The 1000-seed weight is 30-50 g.

Description

• Annual herbs, often strongly tufted.
• Stem (culm) cylindrical, with solid nodes and hollow internodes.
• Leaves in 2 vertical rows at the nodes, with a rounded, auricled sheath, a membranous ligule and a linear, parallel-veined, flat blade; uppermost leaf is called the flag leaf.
• Inflorescence a distichous spike; rachis zigzag, disarticulating (wild species) or tough (cultivars).
• Spikelets solitary at each node of the rachis, awned or awnless, laterally compressed, 3-9-flowered; florets bisexual, the 1 or 2 uppermost ones usually rudimentary, sometimes only 1 of the florets bisexual; disarticulation above the glumes and between the florets; glumes chartaceous, subequal, 5-11-veined, asymmetrically 1-2-keeled, apiculate to awned; lemma rounded on back or keeled at least toward the tip, awned or blunt; palea 2-keeled, ciliate on the keels; lodicules 2, ciliate; stamens 3; pistil with an ovary that is tipped by a small fleshy hairy appendage and with 2 plumose stigmas.
• Fruit an ellipsoid caryopsis; endosperm forms the major part of the fruit; the embryo consists of a disklike scutellum, a conical coleoptile enclosing the plumule with 3 immature leaves and the shoot apex, and a coleorhiza which forms the primary root.

T. aestivum:

• Plant 40-150 cm tall, forming 2-6 seminal roots and many secondary roots, often strongly tillering (up to 40 tillers per plant, depending on cultivar and environment, but normally 2-5).
• Stem smooth, with 4-7 nodes and internodes, sometimes more; internodes becoming larger from bottom to top.
• Leaf blade 15-40 cm × 1-3 cm, glabrous or pubescent.
• Spike 5-15 cm long excluding the awns, varying in shape, size and density; awns, when present, up to 16 cm long.
• Caryopsis ventrally with a central groove, reddish-brown, yellow, white or intermediate hues.

T. turgidum:

• Spike usually bearded and compressed, narrow across the faces, much wider across the 2-rowed profiles.
• Spikelets usually compressed, crowded, imbricate in the lateral rows; glumes 1-keeled, the keel formed by the sharply winged adaxial vein, the other main abaxial vein quite conspicuous but usually not definitely rugose; lemma usually long-awned.

Growth and development

Phasic development of wheat is influenced by temperature, and the cultivar's vernalization and daylength response.

After water has been imbibed, germination begins as the endosperm is broken down to provide nutrients to the emerging coleoptile. Optimum germination occurs between 12-25 °C. The scutellum initially supports early growth and subsequently serves as temporary storage of starch from the endosperm. The seminal roots emerge first. Once the roots start to absorb nutrients and water, the coleoptile emerges 4-6 days after germination. The seminal roots may remain functional for life unless destroyed by diseases or mechanical injury, but they constitute only a small portion of the total root system. The first true leaf of the seedling emerges from the coleoptile. Secondary roots start to develop about two weeks after seedling emergence. They arise from the basal node and form the permanent root system, which spreads out and may penetrate as deep as 2 m, but normally no more than 1 m. Leaf and tiller production increase rapidly soon after crop emergence. Cultivars with tall, weak tillers tend to lodge. All spikebearing tillers eventually flower almost simultaneously.

Flowering begins at the middle third of the spike, then rapidly progressing both upward and downward. Most flowers bloom in midmorning before noon. Wheat is normally selfpollinated; cross pollination is only 1-4%. Pollen is largely shed within the floret. Stigmas remain receptive for 4-13 days. Pollen is viable for up to 30 minutes only. Grains in the centre of the spike and in the proximal florets tend to be larger. Physiological maturity is the stage when the moisture content of the fully formed grain has dropped to 25-35%. The complete crop cycle of spring wheat varies from 80-115 days in SouthEast Asia.

Other botanical information

Triticum consists of a polyploid series of 10-20 species in which there are diploid, tetraploid and hexaploid representatives with chromosome numbers of 2n= 14, 28 and 42. Only the diploids are genetically true Triticum, the others intergeneric hybrids between Triticum and certain species of Aegilops L. Selection at each level has proceeded from wild species to cultivated species whose grain is tightly invested by lemma and palea, and then to free-threshing naked species. There are hardly any cultivated diploids (only some T. monococcum L. cultivars), and no wild hexaploids.

The hexaploid T. aestivum is believed to be of hybrid origin having the genome set AABBDD, with AA originating from T. monococcum or T. urarti Thumanjan ex Gandilyan, BB from Aegilops speltoides Tausch and DD from A. tauschii Cosson (synonym A. squarrosa auct.). Some authors, however, do not agree with this view, since the identity and origin of the B genome is questionable. They contend that the evolutionary history of bread wheat may possibly never be discovered because the introgression that took place to create the present-day constitution of bread wheat is too complex. Some authors keep the genus Aegilops separate from the genus Triticum , others unite the two into Triticum . Bread wheat is a very variable crop, bearing a heavy burden of names and classifications in the taxonomic literature. The distinction of cultivar groups is most appropriate for a purely cultivated complex crop like wheat. About 25 000 cultivars are known. The major cultivar groups are:

• cv. group Aestivum (based on T. aestivum L.; synonyms: T. aestivum L. var. aestivum, T. aestivum L. subsp. vulgare (Vill.) Mac Key, T. vulgare Vill. subsp. vulgare). This is the free-threshing common or bread wheat, thought to have been developed somewhere near the southwestern corner of the Caspian Sea, being the most important cultivar group comprising the majority of the modern wheat cultivars.

• cv. group Compactum (based on T. compactum Host; synonyms: T. aestivum L. subsp. compactum (Host) Mac Key). This is the free-threshing club wheat, developed in Afghanistan and adjacent regions and probably also in Switzerland and Austria.

• cv. group Macha (based on T. macha Dekapr. & Menabde; synonyms: T. aestivum L. subsp. macha (Dekapr. & Menabde) Mac Key, T. spelta L. subsp. macha (Dekapr. & Menabde) V. Dorof.). This is makha wheat, perhaps the oldest hexaploid not free-threshing wheat, indigenous to western Georgia but hardly cultivated any more.

• cv. group Spelta (based on T. spelta L.; synonyms: T. vulgare Vill. subsp. spelta Körn., T. sativum Lamk subsp. spelta Aschers. & Graebn., T. aestivum L. subsp. spelta (L.) Thell.). This is spelt wheat, a not free-threshing wheat, with only 2-3 florets per spikelet, cultivated in small quantities in Europe, Africa and on the plateau of western Iran. It is a wheat that can be cultivated under extreme circumstances, not demanding fertile soils, being relatively disease resistant, and having good taste, food and baking qualities. Before 1850 it was a very important wheat in Europe, declining afterwards but now gaining in popularity in "organic" wheat cultivation.

• cv. group Sphaerococcum (based on T. sphaerococcum Percival; synonyms: T. aestivum L. subsp. sphaerococcum (Perc.) Mac Key). This is the free-threshing Indian dwarf wheat and originated in northwestern India and adjacent regions.

• cv. group Vavilovii (based on T. vavilovii (Tum.) Jakubc.; synonyms: T. vulgare Vill. var. vavilovii Tum. ex Fljaksb., T. aestivum L. subsp. vavilovii (Tum.) Sears). This is the not free-threshing vavilov wheat, indigenous to Armenia, cultivated in small quantities in Asia Minor, Turkey, Armenia and Azerbajdzan. It is characterized by its branching spikelets.

The tetraploid wheats are believed to have a genome from Triticum plus one derived from Aegilops speltoides . The cultivated tetraploid wheats are T. timopheevii Zhuk. cv. group Timopheevii, with genome AAGG, originating from western Georgia and the more important emmer wheat, T. turgidum L., with genome AABB. The following cultivar groups are distinguished in the cultivated emmer wheats:

• cv. group Carthlicum (based on T. carthlicum Nevski; synonyms: T. turgidum L. subsp. carthlicum (Nevski) A. & D. Löve). This is the free-threshing Persian wheat, cultivated in the Caucasus, Georgia, Armenia, Iran and Irak.

• cv. group Dicoccum (based on T. dicoccum Schübler; synonyms: T. vulgare Vill. subsp. dicoccum Körn., T. turgidum L. subsp. dicoccum (Schrank) Thell.). This is emmer, the oldest cultivated wheat, domesticated in the area of Palestine, southwestern Syria and northwestern Jordan. It has dense, bearded spikes, 2-grained spikelets and the grains are not free-threshing. At present it is still cultivated in Ethiopia, Iran, Turkey, Transcaucasia, former Yugoslavia, the Czech Republic, Slovakia and India.

• cv. group Durum (based on T. durum Desf.; synonyms: T. vulgare Vill. subsp. durum Körn., T. aestivum L. subsp. durum (Desf.) Thell., T. turgidum L. subsp. turgidum convar. durum (Desf.) Mac Key). This is the free-threshing durum wheat or macaroni wheat, domesticated in the Mediterranean, and cultivated all over the world in regions with a hot dry climate. It has its greatest diversity in Ethiopia.

• cv. group Polonicum (based on T. polonicum L.; synonyms: T. turgidum L. subsp. polonicum (L.) A. & D. Löve, T. turgidum L. subsp. turgidum convar. polonicum (L.) Mac Key). This is the free-threshing Polish wheat, occasionally cultivated in the same areas as cv. group Durum.

• cv. group Turgidum (based on T. turgidum L.; synonyms: T. vulgare Vill. subsp. turgidum Körn., T. aestivum L. subsp. turgidum (L.) Domin, T. durum Desf. subsp. turgidum (L.) V. Dorof.). This is the free-threshing rivet wheat or cone wheat, cultivated in northern Africa, southern and central Europe, Asia Minor, Pakistan, Iran and Irak.

Triticale (Triticosecale Wittmack) is a cereal derived from hybridization of rye and wheat. After several cycles of selection, the resulting triticale cultivars show characteristics in between wheat and rye. Breeders strive to combine the hardiness of rye with the high yield and quality of wheat. Tetraploid (2n= 28), hexaploid (2n= 42) and octoploid (2n= 56) forms exist, but the hexaploid forms are most successful. As a new food crop, triticale fell short of expectations, but it is becoming increasingly popular as a forage crop. Only where wheat does not grow well because of adverse conditions, triticale is a promising human food crop. It is estimated that it is grown annually on 1.5 milllion ha with Poland, France, Russia and Australia as the main producers.

Ecology

Wheat has a C3cycle photosynthetic pathway and is essentially a temperate climate crop. It requires 1475-1600 growing degree-days (GDD) for a complete crop cycle. Optimum temperatures for development are 10-24°C. Relatively low temperatures result in the highest yields. Temperatures above 35°C stop photosynthesis and growth, and at 40°C the crop is killed by the heat. In tropical areas, wheat is best grown at higher elevations or in the cooler months of the year. The minimum amount of water required for an acceptable crop is 250 mm in the top 1.5 m of soil. Wheat does not grow well under very warm conditions with high relative humidity, unless irradiation and nutrient availability are very favourable. In addition, wheat diseases are generally encouraged by such climatic conditions.

Soils best suited for production are well aerated, well drained, and deep, with 0.5% or more organic matter. Optimum soil pH ranges between 5.5 and 7.5. Wheat is sensitive to soil salinity.

Propagation and planting

Wheat is propagated by seed. It requires a fine seed-bed that is free of weeds. Seed-bed preparation following rice can be labour-intensive and time-consuming. Heat during critical stages should be avoided. Therefore it is crucial to establish and adhere to an optimum planting calendar, to allow the wheat to flower under the most favourable or coolest environmental conditions and hence to maximize yield. If irrigation is not available, then a compromise has to be made by seeding when soil moisture is optimal. Wheat can be sown by hand or machine. When broadcast, the seed is incorporated with a rakelike tool, covered by an animaldrawn plough or incorporated by a machinedrawn disc. The seed may also be dribbled directly into a furrow behind a plow and covered, or machineplanted in rows (spaced at 10-35 cm). Machine drilling uses less seed, promotes uniform germination and stand, and usually gives higher yields. Sowing depth varies from 2-12 cm, with deeper planting required in dry conditions to reach the soil moisture. However, care must be taken not to sow too deep. When using a notill planting machine, rowseeding can be done straight into the stubble of the previous crop. Experiments involving zero or minimum tillage and straw mulching have not led to practical application in South-East Asia. For a rainfed crop, it is recommended to plant when the soil profile is close as possible to being fully charged with moisture, but when there is least risk of monsoon rains. Seeding rate is commonly 100-150 kg/ha, resulting in 250-300 plants/m². The aim is to eventually obtain 400-600 spikes/m². It is advisable to use certified seed that has been treated with fungicides against soil- and seedborne diseases.

Husbandry

Uniform crop stand and early vigour discourage weed growth. In this respect tillering allows the crop to compensate for poor stands and variable weather conditions. Tiller production depends on the formation of secondary roots, plant density, available nutrients and climatic conditions. Yield losses due to weeds are caused by early competition in the first 4-5 weeks. The more common weeds are: Amaranthus spp., Cynodon dactylon (L.) Pers., Cyperus rotundus L., Digitaria spp., Echinochloa spp., Eleusine indica (L.) Gaertner, Eragrostis spp., Portulaca oleracea L., Trianthema portulacastrum L., and volunteer rice. Weeds can be controlled by hand weeding, proper crop rotation, preseeding irrigation, machine cultivation, or application of chemical herbicides.

Irrigation has great potential to increase wheat production. It can be practised in basins, by furrow, or using overhead sprinklers. Care must be taken not to overirrigate since wheat, unlike rice, is very sensitive to early waterlogging. When wheat is grown after rice the risk of waterlogging is considerable, since the rice fields are puddled, which decreases their ability to drain, and since rice farmers are used to applying large amounts of water. Irrigation timing is based either on pre-defined crop stages or on estimates of soil moisture depletion.

The mean nutrient removal per 1 t/ha of grain is 40-43 kg N, 5-8 kg P, 25-35 kg K, 2-4 kg S, 3-4 kg Ca, 3-3.5 kg Mg, and smaller amounts of micronutrients. The exact values depend on the available nutrients and water in the soil, the temperature, and the cultivar. For irrigated wheat in northern Thailand, 60 kg/ha of nitrogen is recommended, 30 kg/ha if rainfed. Responses to phosphorus and potassium are rare or absent in parts of Thailand and the Philippines. Organic manures and composts may be used. Boron deficiency, resulting in grain set failure, has been observed on certain soils. Soil acidity can be a constraint, as observed in wheat production at lower elevations in Indonesia. Liming might raise the pH, but its economics are unknown.

Wheat is best rotated with non-graminaceous crops, particularly with pulses.

Diseases and pests

On average, diseases and pests destroy 20% or more of potential grain harvest either in the field or in storage. The major diseases caused by obligate pathogens of wheat are stem rust (Puccinia graminis f.sp. tritici) and leaf rust (Puccinia recondita f.sp. tritici). In cooler regions, stripe or yellow rust (Puccinia striiformis) may occur. The rusts infect the foliage and sometimes the spikes, resulting in maximum yield losses of 30-50%. The major diseases caused by non-obligate pathogens are spot blotch (Bipolaris sorokiniana), head scab and foot/root rot (Fusarium spp.), and sclerotium foot rot (Sclerotium rolfsii). Regionally important diseases are tan spot (Drechslera triticirepentis), powdery mildew (Erysiphe graminis), speckled leaf blotch (Septoria tritici), glume blotch (Septoria nodorum), alternaria leaf blight (Alternaria spp.), loose smut (Ustilago tritici), rhizoctonia root rot (Rhizoctonia spp.), bacterial leaf streak or black chaff (Xanthomonas campestris pv. undulosa), and BYDV (barley yellow dwarf virus). The most common fungi in stored wheat are various species of Aspergillus and Penicillium .

Field pests include various aphids (which may also transmit viruses), termites, grasshoppers, planthoppers, leafhoppers, bugs, thrips, beetles, grubs, worms, maggots, miners, midgets, sawflies, nematodes (of the roots and the grain), and birds. Storage pests include the rice weevil (Sitophilus oryzae), the lesser grain borer (Rhizopertha dominica), the Angoumois grain moth (Sitotroga cerealella), and the khapra beetle (Trogoderma granarium). Rodents, mainly the black rat (Bandicota bengalensis), also damage stored seeds.

Suitable genetic resistance is available for most diseases. Resistances remain insufficient for spot blotch, several of the root diseases, and most pests. Given the very diseaseconducive environment in South-East Asia, occasional chemical control will probably never be completely eliminated. Seed treatment is usually an economic option.

Harvesting

In South-East Asia wheat is usually harvested with sickles and rarely with machines. A crop harvested at physiological maturity must be dried thoroughly before threshing. Tillers are stacked or spread out to dry in the sun. Threshing, which is more difficult with wheat than with rice, may be done by beating with flails, trampling by humans or animals, or by driving a small tractor over the straw. A wheat sheaf may also be beaten by hand against a low wall, an oil drum, or a wagon bed, so that the grains fall into a container or onto a mat. Grain losses can be considerable with these procedures. Pedal or motordriven paddy rice threshers are also used.

Yield

Commercial yields in South-East Asia vary from 200-300 kg/ha to 2.5 t/ha. Mean yield is estimated at 1 t/ha. At higher elevations (above 1200 m in Indonesia) and the more northern latitudes (northern Vietnam, northern Thailand), experimental yields may reach 3-4 t/ha. Yields tend to be rather low due to high temperature, high humidity, disease pressure, and the low levels of fertilizer applied. Mean yield throughout the developing world is 2.4 t/ha, with the world average only slightly better at 2.5 t/ha. Maximum recorded spring wheat yields are 13 t/ha.

Handling after harvest

After threshing, the straw, chaff, immature grains, sand, stones and other foreign matter are separated from the grain. Laborious, timeconsuming, and less than perfect handwinnowing is the most common cleaning practice in South-East Asia. Lowcost, handdriven or motorized blowers are becoming popular for cleaning and additional drying. Rooftops and highway pavements are also used for drying. A grain moisture content of 13-14% is considered safe for storage. High temperatures and moist conditions may result in spoilage. There are well-designed largescale, commercial seed storage facilities in some Asian countries. On the farm, lowcost seed storage techniques such as tins, metallic drums, earthen jars, or polyethylene containers have been adopted. Bamboo and mud silos are used to store larger amounts of seed. Regular redrying may be necessary to maintain seed viability, if the seed is not stored in an airtight container. Drying in the sun is by far the most common form of insect control, as most insects will leave the grain when temperatures reach 40-44 °C. Control with commercial insecticides is rare because of the costs involved and because seeds for planting and consumption are stored together. Rodents are controlled by keeping them out of the facilities.

Genetic resources

The national wheat programmes in the region generally obtain a considerable part of their germplasm from the International Maize and Wheat Improvement Center (CIMMYT, Mexico) and from the International Center for Agricultural Research in the Dry Areas (ICARDA, Syria). These centres have large breeding programmes, and maintain extensive germplasm collections, including of wild relatives of wheat. Other large national collections are kept in India, the United States and Russia. National breeding programmes maintain key germplasm in storage.

Breeding

Most wheat-producing countries in South-East Asia have established their own National Wheat Programme. Local crossing is rare; the national breeders request germplasm from programmes in neighbouring countries or from CIMMYT or ICARDA. Homozygous advanced lines are mostly requested, but some segregating germplasm is also used. Throughout the region, material is tested in 20-30 different locations. Emphasis is on evaluating performance under high humidity and temperature, in the presence of the major diseases (e.g. Bipolaris or Fusarium).

Prospects

During 1983-1991 per capita wheat consumption in South-East Asia grew by 4.8% per year, and demand is expected to increase further. Wheat is not really a tropical crop and should be promoted as an alternative crop only in the cool, dry season, or in the highlands, preferably with irrigation. Many years of adaptive research are still needed to develop wheat that reliably produces 2-3 t/ha in farmers' fields. Progress is required in the arena of breeding and agronomic research, and also in establishing an attractive pricing and marketing structure for farmers. The crucial factor is a stable and longterm commitment from the respective national governments.

Literature

• Bowden, W.M., 1959. The taxonomy and nomenclature of the wheats, barleys, and ryes and their wild relatives. Canadian Journal of Botany 37: 657-684.
• CIMMYT, 1985. Wheats for more tropical environments. International Maize and Wheat Improvement Center (CIMMYT), Mexico D.F., Mexico. 354 pp.
• Cook, R.J. & Veseth, R.J., 1991. Wheat health management. APS Press, St. Paul, Minnesota, United States. 152 pp.
• Klatt, A.R. (Editor), 1988. Wheat production constraints in tropical environments. International Maize and Wheat Improvement Center (CIMMYT), Mexico D.F., Mexico. 410 pp.
• Larter, E.N., 1995. Triticale. In: Smartt, J. & Simmonds, N.W. (Editors): Evolution of crop plants. 2nd edition. Longman Scientific & Technical, Harlow, United Kingdom. pp. 181-183.
• Lorica, M.V. & Belen, E.H. (Editors), 1986. Wheat review and planning workshop. International Maize and Wheat Improvement Center (CIMMYT) and Philippine Council for Agriculture, Forestry and Natural Resources Research and Development (PCARRD), Los Baños, Laguna, the Philippines. PCARRD Book Series No 38. 161 pp.
• Morris, R. & Sears, E.R., 1967. The cytogenetics of wheat and its relatives. In: Quisenberry, K.S. & Reitz, L.P. (Editors): Wheat and wheat improvement. ASA, Madison, Wisconsin, United States. pp. 19-87.
• Quisenberry, K.S. & Reitz, L.P. (Editors), 1967. Wheat and wheat improvement. ASA, Madison, Wisconsin, United States. 560 pp.
• Saunders, D.A. (Editor), 1991. Wheat for the nontraditional, warm areas. International Maize and Wheat Improvement Center (CIMMYT), Mexico D.F., Mexico. 549 pp.
• Saunders, D.A. & Hettel, G.P. (Editors), 1994. Wheat in heatstressed environments: irrigated, dry areas and ricewheat farming systems. International Maize and Wheat Improvement Center (CIMMYT), Mexico D.F., Mexico. 402 pp.
• Wiese, M.V., 1987. Compendium of wheat diseases. 2nd edition. APS Press, St. Paul, Minnesota, United States. 112 pp.
• Zillinsky, F.J., 1983. Common diseases of small grain cereals: a guide to identification. International Maize and Wheat Improvement Center (CIMMYT), Mexico D.F., Mexico. 141 pp.

Authors

• M. van Ginkel & R.L. Villareal