Prota 1: Cereals and pulses/Céréales et légumes secs
Sp. pl. 1: 84 (1753).
2n = 14
Rye (En). Seigle (Fr). Centeio (Po).
Origin and geographic distribution
The centre of origin of rye is not known exactly, but its current centre of diversity is in the mountainous areas of Afghanistan, Iran and the Middle East. Probably from there, rye was spread to the surrounding areas in Asia, northern Africa and later, just like wheat, to Russia, central and western Europe, where it is cultivated under temperate climatic conditions. Rye is a typical ‘secondary crop’: it was primarily a weed in wheat and barley fields, later adopted as a crop. It may have been domesticated before 3000–4000 BC. Rye grains dating back to 6000 BC have been found in Turkey, but it is not known if these were from crop plants or from weeds. Rye has been spread to all continents, especially to areas with temperate growing conditions. Occasionally it is cultivated at high elevations in the tropics and subtropics. In tropical Africa rye is cultivated in the highlands of East Africa and it has been grown successfully in Malawi. In Ethiopia rye is sparingly grown in the highlands of Arsi, where it was introduced through Swedish projects in the 1960s. Rye has been grown experimentally in Zambia and Mozambique, but apparently with little success. In Nigeria it has been tried as a fodder plant in the 1980s. Rye is also grown in Morocco, Algeria, Egypt and South Africa.
Rye grain is used as a food for humans, but on a worldwide scale it is more important as animal feed. The grain is processed into bread, cakes, crackers etc. For making bread, whole or broken grain can be used; for making cake, the grain needs to be milled. Rye flour is often mixed with wheat flour. In Africa rye flour is considered to make good porridge with an equal amount of maize flour; if used alone, it is considered too sweet. Rye grain can be sprouted to make malt for beer; several alcoholic beverages are prepared by distilling malted rye grains, e.g. rye whiskey in North America and vodka in Poland and Russia. Rye flour is used as filler for thickening soups and sauces.
Rye grain is used as a fodder, especially in pig husbandry. Starch from the grain is industrially used in the production of glue, matches, gum for sizing paper, and plastics. Rye straw is harvested for feed (cattle), litter (in livestock sheds), thatching, mulching material, industrial use (paper/cardboard), packing material (nursery plants, cheese) and fuel. Immature rye is harvested as a whole crop forage and it is grown as a green manure or cover crop. In Europe and India rye is sometimes grown as a host plant for ergot (Claviceps purpurea), which is used medicinally, e.g. against migraine. Rye pollen extracts are registered and commercially available as a medicine against benign prostatic hyperplasia in western Europe, Japan, Korea and Argentina. In Europe rye is under investigation as a biomass energy crop.
Production and international trade
According to FAO statistics, the total world rye production in 1999–2003 amounted to 20 million t/year from 9 million ha. The main producers are the Russian Federation (5.6 million t/year from 3.2 million ha), Poland (4.2 million t/year from 1.9 million ha) and Germany (3.9 million t/year from 0.7 million ha). No production statistics are available for tropical Africa. World rye exports in 1998–2002 amounted to about 1.8 million t/year. The main exporter was Germany (1.1 million t/year); the main importers were Japan (360,000 t/year), the Russian Federation (170,000 t/year), South Korea (170,000 t/year) and China (140,000 t/year).
Rye contains per 100 g edible portion: water 11.0 g, energy 1402 kJ (335 kcal), protein 14.8 g, fat 2.5 g, carbohydrate 69.8 g, dietary fibre 14.6 g, Ca 33 mg, Mg 121 mg, P 374 mg, Fe 2.7 mg, Zn 3.7 mg, vitamin A 11 IU, thiamin 0.32 mg, riboflavin 0.25 mg, niacin 4.3 mg, vitamin B6 0.29 mg, folate 60 μg and ascorbic acid 0 mg. The essential amino-acid composition per 100 g edible portion is: tryptophan 154 mg, lysine 605 mg, methionine 248 mg, phenylalanine 674 mg, threonine 532 mg, valine 747 mg, leucine 980 mg and isoleucine 549 mg (USDA, 2004). Rye cultivars comparatively rich in lysine are known. The main fatty acids are (per 100 g edible portion): linoleic acid 958 mg, oleic acid 280 mg, palmitic acid 271 mg and linolenic acid 147 mg. Due to the limited gluten content, bread made from rye flour has a compact structure; rye grain or grit is usually combined with wheat flour to improve the volume and texture of the bread. Because rye is not gluten-free, it is not suitable for inclusion in the diet of people with coeliac disease.
Rye starch has a high water-absorbing capacity, making it suitable for use in adhesives. The feed value of rye grain is lower than that of other cereal grains, due to decreased feed intake, of which the causes are unclear. Therefore rye is used in mixtures with other grains. Rye straw is not very suitable as fodder because it is tough and fibrous. In a study on forage quality in the United States, the crude protein content of whole rye plants declined from 27.8% in the vegetative stage through 24.2% in the booting stage to 13.4% in the heading stage; the in-vitro dry matter digestibility in these three stages was 79%, 81% and 70%, respectively.
Although rye pollen extracts are used to treat benign prostatic hyperplasia, results from long-term studies are not available and a meta-study did not show sufficiently strong evidence.
Rye, its residues and aqueous extracts have allelopathic properties, enhancing the suitability of rye for use as a weed-suppressing cover crop. The main allelopathic compounds are 2,4-dihydroxy-1,4(2H)-benzoxazin-3-one and its decomposition product 2(3H)-benzoxazolinone. Weed-control effects of a rye mulch remain for 30–75 days after the rye is killed.
Annual tufted grass up to 1.5(–3) m tall, often blue-green; stem (culm) erect, slender, hollow except at nodes, glabrous but pubescent near the spike, producing tillers and roots at base; root system extensive, penetrating to 2 m depth. Leaves alternate, simple; leaf sheath long and loose, with small auricles; ligule short, jagged; blade linear-lanceolate, 10–20 cm × 1–2 cm, smooth or slightly scabrous. Inflorescence a terminal spike 7–15 cm long, curved, much awned, with spikelets alternating and closely inserted on a long zigzag rachis. Spikelets 2-flowered, with bisexual florets; glumes subulate, 1-veined, up to 1 cm long; lemma lanceolate, up to 2 cm long, tapering into a 2–8 cm long awn, 3(–5)-veined, keel prominently set with stiff bristles; palea about as long as lemma, awnless, scabrid on the keel; stamens 3; ovary superior, with 2 plumose stigmas. Fruit a caryopsis (grain), oblongoid, 4.5–10 mm × 1.5–3.5 mm, narrowly grooved, short-pointed, pale brown, glabrous.
Other botanical information
Secale comprises 3 species, and is distributed from eastern Europe to central Asia, with 1 species also occurring in South Africa. Only Secale cereale is cultivated. Secale strictum (C.Presl) C.Presl subsp. africanum (Stapf) K.Hammer (synonym: Secale africanum Stapf) is only found in a single locality in South Africa. It is recordedly eaten as a cereal. It is liked by livestock and birds and is considered a potential pasture plant.
In the literature 2 subspecies have been distinguished within Secale cereale: subsp. cereale (comprising the cultivated types, with a tough rachis) and subsp. ancestrale Zhuk. (comprising the wild and weedy types, with a more or less fragile rachis, mainly found in western Asia). However, more subspecies have also been distinguished. Within cultivated rye there are many landraces (usually with long culms and small grains) and cultivars.
Hybrids of rye and wheat called triticale (× Triticosecale) have been developed and these show a mix of characteristics from the parents, combining the hardiness of rye with the high yield and quality of wheat. Triticale is presently grown only locally in tropical Africa, e.g. in Ethiopia, Kenya, Tanzania and Madagascar, and also in northern Africa and South Africa. As a new food crop, it fell short of expectations, but it is becoming increasingly popular as a forage crop.
Growth and development
Rye germinates within 4 days at a soil temperature of 4–5°C, and more rapidly at higher temperatures. At the appearance of the fourth leaf, tillers and roots are formed to anchor the plant. Shoot initiation ceases as the plant enters the reproductive stage. Then, stem elongation starts and initiation and differentiation of the inflorescence take place. In each spike 40–45 spikelets are initiated, 30–35 of which bear 1–2 grains, resulting in 45–55 grains per spike. Flowering lasts 3–5 days for a spike and 8–12 days for a rye crop. Rye is cross-pollinated by wind. The post-floral period for grain-filling is 4–5 weeks. The period from sowing to harvesting varies from 4–10 months. The duration of growth is largely dependent on temperature during reproductive development. In temperate regions so-called winter rye is planted in autumn to receive sufficient cold and short days to induce vernalization and reproductive growth; spring rye is planted in early spring and can be harvested after 4–6 months.
Rye is a crop of temperate climates; in the tropics it is grown at high altitudes, e.g. at 3000–3900 m in Ethiopia. Seedlings can endure frost down to –25°C. Tillering, shoot growth and flower initiation require rather low temperatures (10–15°C); for adequate growth during reproductive development the mean daily temperature must not exceed 20°C. Rye is tolerant to drought. Flowering is favoured by dry and sunny weather. Continuous rain, high humidity and low temperatures hamper pollination, causing incomplete grain set. Winter rye is a long-day plant; the reproductive development is stimulated by daylength increasing from 14 to 20 hours. Therefore, winter rye is mainly grown between 40–65°N. Cultivars of spring rye are occasionally grown at high elevations in subtropical and tropical areas. They are less sensitive to daylength and do not need vernalization. Their flowering and seed set are satisfactory at a daylength of 12–13 hours. Rye can be grown on most well-aerated soil types with a pH from 5–7.5; it is mainly grown on light, sandy and peaty soils.
Propagation and planting
Rye is propagated by seed. The 1000-seed weight is 20–40 g. The optimal planting time for winter rye usually ranges from mid-September until mid-October in Europe. Seed can be broadcast by hand but needs to be covered to achieve adequate germination. Better conditions are created by drilling seed mechanically at a uniform depth of 2–4 cm in rows 10–25 cm apart. Seed rates range from 100–150 kg/ha to obtain an optimal density of 200–300 plants/m2. Spring rye needs to be planted as early as possible, if necessary even during winter, if soil conditions are suitable for preparing a seed-bed. Spring rye tillers poorly, so requires a higher seed rate (150–200 kg/ha) than winter rye.
Rye competes strongly with weeds, but they can cause problems at harvest. They can be controlled mechanically by harrowing or hoeing, or by herbicides during the tillering stage. Lodging can cause considerable damage. The amount of fertilizer required is largely related to the expected yield; about 20 kg N, 4 kg P and 13 kg K are removed from the soil per t grain yield. About 75–80% of the N and P is removed with the grains, whereas 75% of the K remains in the straw. N is often the most yield-limiting nutrient. For yields over 5 t/ha a split N-application is preferred.
Diseases and pests
Rye is considered relatively tolerant to diseases. Nevertheless, after germination snow mould (Fusarium nivale) can cause considerable plant losses and brown or leaf rust (Puccinia recondita f.sp. secalis) can severely damage leaves and stems. The most conspicuous disease is ergot (Claviceps purpurea), which infects the grain especially when grain set is poor; it produces alkaloid-containing sclerotia. Grains with ergot are toxic, causing gangrenous or convulsive ergotism, and can make a rye stock unsuitable for human and animal consumption. No sources of resistance to ergot have yet been identified in rye. Other diseases include eyespot (Pseudocercosporella herpotrichoides), sharp eyespot (Rhizoctonia solani), powdery mildew (Erysiphe graminis), stem rust (Puccinia graminis), glume blotch (Septoria nodorum) and leaf blotch (Rynchosporium secalis). Most fungal diseases can be controlled by fungicides, but damage by snow mould, sharp eyespot and ergot can only be restricted by using healthy and disinfected seed. Resistance, e.g. to leaf rust and stem rust, is found in several rye cultivars, and resistance to these diseases has been transferred from rye to wheat through intergeneric crosses. Damage by viruses is of minor importance. The nematode Ditylenchus dipsaci can affect rye, but it is not common. Insect pests are not important in rye cultivation.
Time of harvest of rye is mid-summer in Europe when the moisture content of the grain is below 15%. The crop can be harvested by hand; the method of harvesting, threshing, collecting and storing can be similar to that used for sorghum and millets. For combine harvesting, it is best to wait until the moisture content has dropped below 16%. However, to prevent loss of quality due to sprouting in the ear, the crop may be harvested at a higher moisture content (18–20%), especially if wet weather conditions prevail and delay ripening. Then subsequent drying will be required, in sheaves in the field or mechanically during storage.
Rye yields vary widely, from less than 1 t/ha in Africa, Latin America and Australia to over 5 t/ha in some western European countries. The world average yield is about 2 t/ha.
Handling after harvest
Low moisture content of the rye grain and low storage temperatures are desirable for long-term storage. The moisture content of the grain should be less than 13% if rye is to be stored for 6 months (without ventilation) at 15°C. If the stock is regularly ventilated, a moisture content of 14–15% may be acceptable. In temperate regions, such low moisture contents are often not reached at harvesting, and grain needs to be dried by warm air. Cleaning is commonly done before or during storage. After drying in the field, straw is usually baled and stored in barns or stacks for later use.
Large germplasm collections of rye are kept in the Russian Federation (N.I. Vavilov All Russian Scientific Research Institute of Plant Industry, St. Petersburg, 2635 accessions), Germany (Institute for Plant Genetics and Crop Plant Research (IPK), Gatersleben, 1990 accessions), the United States (USDA-ARS National Small Grains Germplasm Research Facility, Aberdeen, Idaho, 1823 accessions) and Poland (Plant Breeding and Acclimatization Institute (IHAR), Radzikow, Blonie, 1366 accessions; Botanical Garden of the Polish Academy of Sciences, Warsaw, 1362 accessions). The only rye germplasm collections in Africa recorded by IPGRI are in South Africa (Division of Plant and Seed Control, Department of Agriculture Technical Service, Pretoria, 178 accessions; Small Grain Institute, Bethlehem, 52 accessions).
Rye breeding programmes have given priority to winter types, and aspects as winter hardiness, straw stiffness, disease resistance and resistance to sprouting in the ear have received much attention. These breeding efforts have resulted in a considerable increase in grain yield and yield stability, shorter plants, reduced lodging and enhanced harvest index. Well-known cultivars include ‘Petkus’, ‘Pearl’, ‘Steel’ and ‘King II’. Efforts to exploit heterosis for enhancing grain yield have resulted in hybrids that have entered commercial production with high-input management. Hybrids outyield conventional cultivars by 10–20%, but they demand more inputs (seed, crop protection). Tetraploid cultivars have been developed, with more vigorous growth and larger grains. Secale cereale has been crossed with Secale strictum with the objective of improving winter hardiness and resistance to drought and diseases. Perennial rye cultivars, intended for use as fodder, have also been developed by crossing the two species. For the production of ergot, male-sterile lines are used, facilitating the infection by the fungus.
Rye is considered one of the most recalcitrant plants for tissue culture and genetic transformation. However, systems for the stable genetic transformation of rye using Agrobacterium tumefaciens or biolistic methods have been developed. It is possible to obtain large numbers of genetically identical plants by in-vitro regeneration using immature inflorescences as explants. Genetic linkage maps of rye, on the basis of various marker types (RFLPs, AFLPs, RAPDs and microsatellite markers) have also been constructed. Genes conferring resistance to leaf rust have been identified.
Rye may be inferior in several ways to the predominant world cereals (wheat, rice and maize), but it will continue to be an important crop because of its winter hardiness, tolerance to drought, ability to grow on poor soils, and consumer demand for baked products with the unique flavour of rye. There is considerable scope for improving yields. The application of high quality seed, new (hybrid) cultivars and advanced management practices can increase yield levels in the short term. The prospects of rye in tropical Africa seem limited. It has been tried in various countries, but its cultivation has not become important.
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Sources of illustration
• Darwinkel, A., 1996. Secale cereale L. In: Grubben, G.J.H. & Partohardjono, S. (Editors). Plant Resources of South-East Asia No 10. Cereals. Backhuys Publishers, Leiden, Netherlands. pp. 123–127.
Correct citation of this article:
Brink, M., 2006. Secale cereale L. In: Brink, M. & Belay, G. (Editors). PROTA 1: Cereals and pulses/Céréales et légumes secs. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, plant habit; 2, flowering spikelet; 3, floret without lemma; 4, fruiting spikelet; 5, grains.
detail of inflorescence
transport from the field