Secale cereale (PROSEA)
- Protologue: Sp. pl.: 84 (1753).
- Family: Gramineae
- Chromosome number: 2n= 14
- Rye (En)
- Seigle (Fr)
- Indonesia: gandum hitam.
Origin and geographic distribution
Rye is known only from cultivation. The gene centre of rye is located in the mountainous areas of Afghanistan, Iran and the Middle East, from which other small-grain crops like wheat, barley and oats also originated. From there, rye was spread to the surrounding areas in Asia (Iraq, Turkey), northern Africa and later, just like wheat, to Russia, Central and West Europe, where it is cultivated under temperate climatic conditions. Due to its hardiness to drought and frost, rye was spread well beyond 60 °N. It 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, e.g. in East and South Africa.
Rye kernels are used as a foodstuff for humans, but are more important as animal feed. Rye is processed for making bread and cakes. Whole or broken kernels are used for bread-making; for cake-making, the kernels need to be milled. Rye flour is often mixed with wheat flour. Several alcoholic beverages are prepared by distilling malted rye grain. Rye is used as a component in fodder, especially in pig husbandry. The straw is harvested for feed (cattle), litter (in livestock sheds), mulching material, industrial use (paper/cardboard) and even for fuel.
On a small scale, immature rye is harvested as a whole crop for animal feed or it is grown as a green manure crop.
Production and international trade
In 1993, more than 13 million ha of rye was grown worldwide, with a total production of about 26 million t. Cultivation of rye is mainly concentrated in the Russian Federation (6 million ha/9 million t) and Europe (3.7 million ha/10 million t), of which 50% in Poland. In Asia, 0.65 million ha are cultivated, with a production of 0.9 million t. No data are available on area and production in South-East Asia.
Rye enters world trade on a small scale; it is commonly grown for domestic consumption and to feed livestock on the farm.
The chemical composition of 100 g edible portion is approximately: water 14 g, protein 11 g, fat 2 g, carbohydrates 69 g, fibre 2 g and ash 2 g. The protein content varies from 8-12%. The protein fraction contains relatively high contents of lysine and threonine. Due to the lack of gluten, bread made from rye has a compact structure. 1000-kernel weight ranges from 30-40 g.
- Annual (spring rye) or biennial (winter rye) tufted herb, 1-1.5(-3) m tall, often blueish-green in colour. Root system extensive, penetrating to 1-2 m depth.
- Culm erect, slender, glabrous except pubescent near the spike, with 6-7 (spring rye) and 10-12 (winter rye) nodes of which the 5-6 basal ones are very close, with hollow internodes; one leaf is produced at each node, the basic nodes also producing shoots or tillers and crown roots.
- Leaf sheath long and loose; ligule short, jagged; auricles short and small; blade linear-lanceolate, 10-20 cm × 1-2 cm, smooth or slightly scabrous.
- Inflorescence a terminal spike, 7-15 cm long, curved, much awned, narrow but close-flowered.
- Spikelet with 2 fertile florets, alternating on a long zigzag rachis; glumes subulate, 1-veined, up to 1 cm long; lemma up to 18 mm long, narrow, tapering into a 2-8 cm long awn, 3(-5)-veined, keel prominently set with stiff teeth; palea scabrid on the keel; stamens 3, pistil 1 with 2 plumose stigmas.
- Caryopsis oblongoid, 5-9 mm long, light brown, narrowly grooved, short-pointed, glabrous.
Growth and development
First, the coleoptile emerges from the soil and leaves are formed. At the appearance of the fourth leaf, tillers and crown roots are formed to anchor the plant. Initiation and formation of shoots (tillering) enables the crop to compensate for low plant densities. 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 kernels, resulting in 45-55 kernels per spike. Flowering lasts 3-5 days for a spike and 8-12 days for a rye crop. The post-floral period for grain-filling is 4-5 weeks. The period from sowing to harvesting varies from 7-10 months for winter rye and from 4-6 months for spring rye. The duration of growth is largely dependent on temperature during reproductive development. Winter rye is planted in autumn to receive sufficient cold and short days to induce vernalization and reproductive growth.
Other botanical information
There are many landraces (usually with longer culms and smaller grains) and cultivars. Well-known cultivars include "Petkus", "Pearl", "Steel" and "King II".
Cultivated rye is assumed to have developed from Secale montanum Guss., a perennial, wild, outbreeding species of mountainous regions in the Mediterranean and Central Asia.
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 million ha with Poland, France, Russia and Australia as the main producers.
Rye is the most tolerant among the small-grain cereals of variations in (low) temperature, water supply and soil type. It germinates at a soil temperature of 4-5 °C within 4 days and the seedlings can endure frost during winter down to -25 °C. Vernalization occurs naturally. 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. The demand for water is relatively low; rye is more tolerant of water stress than other small-grain cereals. Flowering is favoured by dry and sunny weather. Continuous rain, high humidity and low temperatures hamper pollination, causing incomplete grain set. Rye is a cross-pollinated crop, depending on wind for the spread of pollen. It is suited for growth under temperate and continental climatic conditions. 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 40-65N. Cultivars of spring rye are occasionally grown at high elevations in subtropical and tropical areas. They are less sensitive to long daylength and do not need vernalization. Their flowering and seedset 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. Fertile clay soils are usually reserved for more productive crops, such as wheat.
Propagation and planting
Seed for sowing must be of good quality to ensure optimal germination and favourable crop growth. It is advisable to treat the seed with a fungicide. At the onset of the winter frosts the rye needs to have reached the tillering stage, to ensure good winter hardiness and productivity. Therefore, the optimal planting time for winter rye depends on growing conditions in autumn, but 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. Depending on sowing time and soil conditions, the seed rate ranges 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, when soil conditions are suitable for preparing a seed-bed. Spring rye tillers poorly, so requires a higher seed rate (150-200 kg/ha).
Rye competes strongly with weeds. In spite of small yield reductions, weeds can cause problems at harvesting. They can be controlled mechanically by harrowing or hoeing, but most effectively by herbicides during the tillering stage. Considerable damage can be caused by lodging, which is common in dense and leafy crop stands.
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 kernel yield. Nitrogen is often the most yield-limiting nutrient. Fertilizers can be best given at the onset of crop growth in early spring. Nitrogen is taken up slowly during vegetative growth, but quickly during stem elongation. For yields over 5 t/ha a split N-application is preferred. The demand for micronutrients is small; shortages can be remedied by liquid application, but this may not be feasible for smallholders.
Rye fits well into crop rotation systems as an anterior crop as well as a posterior crop. Even continuous cropping is often possible.
Diseases and pests
Rye is considered to be a relatively tolerant cereal. Nevertheless, after germination snow mould (Fusarium nivale) can cause considerable plant losses and brown rust (Puccinia recondita) can severely damage leaves and stem. But the most conspicuous disease is ergot (Claviceps purpurea), which infects the kernel especially when grain set is poor. Ergot kernels are toxic and can make a rye stock unsuitable for human and animal consumption. Other diseases are e.g. 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.
Damage by insects and viruses is of minor importance. Only the nematode Ditylenchus dipsaci can damage rye, but it is not common.
Time of harvest is mid-summer in Europe when leaves are dead, stems yellowish-brown and the moisture content of the kernel is below 15%. Kernels at this moisture content can be stored for a long time. For combine harvesting, it is best to wait until the moisture content has dropped below 16%. However, to prevent loss of quality due to pre-sprouting, the crop may be harvested at a higher moisture content (18-20%), especially if wet weather conditions prevail and are delaying ripening. Then subsequent drying will be required, in sheaves in the field or mechanically during storage.
The crop can also be harvested by hand; the method of harvesting, threshing, collecting and storing is similar to that used for small-grain cereals like sorghum and millets.
Kernel yields vary widely, from less than 1 t/ha (Africa, Latin America) to well over 5 t/ha (some West European countries). Growing conditions and cultivation techniques largely determine the yield; poor management hampers crop growth and severely reduces yield. In West Europe, kernel yields of 8-9 t/ha are attainable in farmers' fields.
Handling after harvest
Low moisture content of the grain and low storage temperatures are desirable for long-term storage. The moisture content of the kernel should be less than 13% if rye is to be stored for six 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 kernels need 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.
In countries with substantial areas under rye germplasm collections are maintained at research institutes and at private breeding stations, and used in national and international breeding programmes. International institutes such as the International Maize and Wheat Improvement Center (CIMMYT) in Mexico, play a major role for breeding programmes in tropical regions, as conservators and suppliers of germplasm.
There is a great variety of rye cultivars, most of which are adapted to or bred for particular geographical areas. Rye breeding programmes have given priority to winter types, and aspects as winter hardiness, straw stiffness, disease resistance and pre-sprouting resistance have received much attention. Breeding for (baking) quality has been restricted to reducing the pre-sprouting. These breeding efforts have resulted in a considerable increase in grain yield and yield stability, shorter plants, reduced lodging and enhanced grain/straw ratio. Efforts to exploit heterosis for enhancing grain yield have resulted in hybrids that have entered commercial production with high-input management in recent years. Hybrids outyield conventional cultivars by 10-20%, but they demand more inputs (seed, crop protection).
Winter rye is the most hardy and least susceptible to drought, diseases and pests of all cereals. Consequently, rye will remain an important cereal crop in continental climatic zones on light soils of moderate fertility and water-retaining capacity. Under such suboptimal growing conditions, rye has proved to be a productive and reliable cereal crop. There is considerable scope for improving yields, especially in areas with a low productivity. The application of high quality seed, new (hybrid) cultivars and advanced management practices can increase yield levels in the short term.
Since rye is potentially an interesting cereal crop for South-East Asia (especially for highland areas well over 1500 m altitude), its prospects merit further investigation.
- Adolf, K. & Riemann, K.H., 1989. Züchtung und Produktion von Winterroggen [Breeding and production of winter rye]. Fortschrittberichte für die Landwirtschaft und Nahrungsgüterwirtschaft 27: 1-35.
- Aufhammer, W. & Kübler, E., 1989. Zur Ertragsbildung von Populations- und Hybrid-roggensorten (Secale cereale L.) bei differenzierten Bestandesaufbau [Yield formation in population and hybrid cultivars of rye at various densities]. Zeitschrift für Landwirtschaftlicher Forschung 40: 207-220.
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- Brouwer, W., 1972. Handbuch des Speziellen Pflanzenbaues I: Roggen [Handbook of special crop growing I: Rye]. Paul Parey, Berlin and Hamburg, Germany. pp. 203-270.
- Bushuk, W., 1976. Rye: production, chemistry and technology. American Association of Cereal Chemists Inc., St. Paul, Minnesota, United States. 181 pp.
- Geisler, G., 1983. Ertragsphysiologie von Kulturarten des gemäszigten Klimas [Yield physiology in cultivated crops of temperate climates]. Paul Parey, Berlin and Hamburg, Germany. pp. 12-68.
- Heyland, K.U. & Aufhammer, W., 1973. Zur Ertragsbildung bei Winterroggen [Yield formation in winter rye]. Zeitschrift für Acker- und Pflanzenbau 137: 96-122.
- 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.
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- A. Darwinkel