Helianthus annuus (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Carbohydrate / starch|
|Forage / feed|
- Protologue: Sp. pl. 2: 904 (1753).
- Family: Asteraceae (Compositae)
- Chromosome number: 2n = 34
- Sunflower (En).
- Tournesol (Fr).
- Girassol (Po).
- Alizeti (Sw).
Origin and geographic distribution
Wild Helianthus annuus spread from its origin in the south-western United States to most other regions of North America in association with human migration in prehistoric times. According to archaeological evidence, modern single-headed sunflowers are derived from types first domesticated in central North America more than 5000 years ago. European explorers of the 16th century found very tall and large-headed sunflowers widely used as food and as a source of oil. Sunflower became popular in Europe as a novel ornamental soon after its first arrival from Mexico in the botanic garden of Madrid around 1510. Its potential as an oilseed crop for higher latitudes became apparent in the 18th century in Russia, and by 1880 sunflower was grown on some 150,000 ha mainly in the Ukraine and Caucasus regions for the manufacture of edible vegetable oil. In the Soviet Union of the 1930s more than 3 million ha of sunflower were harvested annually against 0.5 million ha in the remainder of Europe, particularly Hungary and the Balkan Peninsula. Breeding programmes in the Soviet Union developed high-yielding and oil-rich sunflower cultivars, which played a crucial role in the expansion of sunflower production in Europe and elsewhere between 1920 and 1970. Modern sunflower production in North and South America (mainly the United States, Canada and Argentina) developed from sunflower types re-introduced by immigrants from Eastern Europe and Russia at the end of the 19th century and from Russian cultivars brought in after 1960. The application of F1-hybrid seed technology in combination with dwarf and semi-dwarf plant habits, high oil content of the seed and host resistance to diseases and pests have been major factors leading to the spectacular increase of sunflower production since 1980 in Argentina, India, China, Turkey, the European Union (e.g. France, Spain) and South Africa. Sunflower production in tropical Africa is expanding mainly in the highlands of eastern and southern countries. Occasionally sunflower escapes and becomes naturalized, also in tropical Africa.
Sunflower seed yields an edible oil of excellent quality due to a high proportion of unsaturated fatty acids, near absence of toxic substances, light colour, and good taste and flavour. The oil is used mainly as cooking and salad oil and in the manufacture of margarine, sometimes as a pure sunflower product, but more often in blends with other vegetable oils. Inferior grades of sunflower oil find application as drying oils for paints and varnishes, and in the manufacture of soap. The main by-product of sunflower oil extraction is a protein-rich meal used as livestock feed. For this purpose, the meal is commonly blended with soybean meal. Defatted sunflower meal is also suitable for human consumption and has been used as a partial substitute for wheat flour in baking bread and cakes. When oil is extracted industrially, the stalk and flower head of sunflower are processed into cellulose and fibre mats. The indigenous peoples of North America have had a long tradition of preparing bread-like products from ground sunflower seeds.
The seeds (botanically fruits) of non-oil cultivars, which are larger and often black and white striped, are consumed directly. Generally, the largest 25% fraction of the seeds are consumed as salted and roasted snacks, the medium 30–50% fraction as hulled kernels in various confectionery and bakery products, and the smallest seeds are birdseed and pet food.
Sunflower is sometimes cultivated as a forage crop. In comparison with maize, it requires a shorter growing season, is more drought tolerant and produces lower yields but a silage of often slightly superior quality. Sunflower is also grown as an ornamental garden and pot plant and is an important bee plant.
Production and international trade
Average annual world production of sunflower seed over the period 2002–2004 was about 26.2 million t, equivalent to 9.8 million t oil, from 21.4 million ha in 66 countries. The Russian Federation (4.3 million t) is the largest producer, followed by Ukraine (3.7 million t), Argentina (3.6 million t), China (1.9 million t), France (1.5 million t), Romania (1.4 million t), USA (1.2 million t), India (1.1 million t), Hungary (1.0 million t), South Africa (800,000 t), Spain (780,000 t) and Turkey (750,000 t). Countries in tropical Africa with sizable sunflower production are Tanzania (28,000 t), Sudan (18,000 t), Kenya (12,000 t), Angola, Mozambique and Zambia (each about 11,000 t).
Most sunflower oil is consumed in the countries of origin and only 30% reaches the international market; the European Union absorbs about two-thirds of it. Important exporting countries are Argentina, the United States and Hungary. The 9–10 million t of sunflower presscake are also of considerable commercial value. The oil represents about 75% and the meal 25% of the total value of sunflower oilseed production. Most of the sunflower meal is traded on domestic markets, except for the 1.0–1.5 million t imported annually into the European Union from Argentina. Non-oilseed production of sunflower represents only 5–10% of the total production.
The composition of 100 g dry sunflower seed is approximately: water 5 g, protein 23 g, oil 50 g, carbohydrate 19 g, dietary fibre 11 g, Ca 116 mg, Mg 354 mg, P 705 mg, Fe 6.8 mg, Zn 5.1 mg, thiamin 2.3 mg, riboflavin 0.25 mg, niacin 4.5 mg, folate 22.7 μg, ascorbic acid 1.4 mg (USDA, 2005). Oilseed sunflower cultivars have a high oil content (>50%) and low hull fraction (20–25%), against a low oil content (25–30%) and high hull fraction (43–52%) of non-oilseed cultivars. About 98% of all the oil is contained in the seed (kernel) and 1–2% in the hull. The fatty acids of traditional sunflower oil are palmitic acid 5–7%, stearic acid 3–6%, oleic acid 16–36%, linoleic acid 61–73% and only traces of linolenic acid. The composition of recently developed ‘high-oleic’ sunflower cultivars is different: palmitic acid 3–4%, stearic acid 4–5%, oleic acid 80–90% and linoleic acid 3–9%. Such oil is less susceptible to oxidative degradation than oil with a high polyunsaturated linoleic acid content. Unrefined sunflower oil contains 630–700 mg/kg tocopherols (fat-soluble vitamin E).
Sunflower meal has a protein content of 29–45% depending on cultivar and method of oil extraction and is a good source of Ca, P and vitamin B complex. Sunflower proteins are highly digestible and have a good biological value, but are somewhat deficient in the essential amino acid lysine. Chlorogenic acid is the main antinutritional factor in sunflower meal, but at a concentration lower than 6 g/kg it does not affect the nutritional quality. Stem and husk are rich in K and the forage contains: protein 9%, fibre 20% and ash 15%.
- Erect annual herb up to 4(–5) m tall, long-hairy; taproot strong, up to 3 m deep with numerous lateral roots 60–150 cm long in the top 40–60 cm of the soil; stem erect, but slightly to sharply curved below the flower head in mature plants, 3–6 cm in diameter, terete but with ridges, branched in many wild types, unbranched in most cultivated types, woody and angular at maturity and often becoming hollow.
- Leaves opposite in lower part of plant, higher ones arranged spirally, simple; stipules absent; petiole long; blade of lower leaves cordate, of higher ones ovate, 10–30 cm × 5–20 cm, apex acute or acuminate, margin toothed, hairy on both sides with glandular and non-glandular hairs, veins prominent and forming a reticulate pattern.
- Inflorescence a terminal head 10–50 cm in diameter, sometimes drooping when mature; receptacle flat to concave, 1–4 cm thick; involucral bracts arranged in 3 rows, ovate to ovate-lanceolate, ciliate.
- Ray florets sterile, showy, deciduous, corolla ligulate, elliptical, c. 6 cm × 2 cm, usually yellow; disk florets bisexual, numerous, arranged in spiral whorls from the centre of the head, c. 2 cm long, subtended by a pointed palea, pappus scales 2, chaff-like, deciduous, corolla tubular, 5-lobed, brown or purplish, stamens 5, filaments flattened, free, anthers long, fused into a tube, ovary inferior, pubescent, style long with nectaries at its base, stigma with 2 curved lobes.
- Fruit an obovoid achene 7–25 mm × 4–15 mm × 3–8 mm, flattened, slightly 4-angled with rounded base and truncate tip, white, cream, brown, purple, black or white-grey with black stripes.
- Seed with thin seed coat adnate to the fruit wall.
- Seedling with epigeal germination; hypocotyl 6–8 cm long, epicotyl c. 0.5 cm long, hairy; cotyledons stalked, leafy, 2.5–3 cm long, glabrous.
Other botanical information
Helianthus comprises about 50 species, all from North America. These are grouped in 4 sections, one being the section Helianthus with 11 annual, diploid species including the domesticated sunflower. Cultivars are usually grouped according to plant height:
– Tall (Giant) cultivars: 2–4 m tall, flowerheads 30–50 cm in diameter and large seeds, late maturing, oil content rather low; representative: ‘Mammoth Russian’;
– Standard cultivars: 1.5–2.1 m; representatives: ‘Peredovic’, ‘VNIIMK 8931’ and ‘Progress’, of Russian origin, with high oil content;
– Semi-dwarf cultivars: 1.2–1.5 m, early maturing, shorter internodes but the same number of leaves as standard cultivars; heads 17–22 cm in diameter; representatives: ‘Pole Star’, ‘Jupiter’, most modern hybrid cultivars;
– Dwarf cultivars: 0.8–1.2 m tall, with fewer nodes and leaves than standard cultivars but normal internode length; flower heads 13–17 cm in diameter and small seeds, highest oil content; representatives: ‘Advance, ‘Sunrise’.
Growth and development
Sunflower seeds show dormancy until 30–50 days after harvesting, but this is easily overcome by rinsing in water or exposure to ethylene prior to sowing. Dry seeds stored below 10°C at 50% relative humidity will retain their viability for several years. The growth cycle is usually about 4 months, but it ranges from 75–180 days depending on the environment and genotype. Sowing to seedling emergence takes 5–10 days, emergence to floral initiation 15–20 days, floral initiation to first flowering 20–90 days, flowering 5–15 days and flowering to seed maturity 30–45 days. Floral initiation occurs around the 8th leaf stage. Pronounced heliotropism is a characteristic of sunflower. Young heads and leaves face east in the morning and follow the movement of the sun to face west in the evening. This heliotropism decreases gradually during flowering with most mature heads eventually facing east. Anthesis progresses from the periphery of the head inwards at 1–4 rows of florets per day. Anthesis of a floret starts early in the morning and is protandrous; the style extends through the anther tube, pushing the pollen outside; the stigma becomes fully extended and receptive the following morning. Pollination is mainly by honeybees and bumblebees. Fertilization is complete by the evening of the second day. Sunflower is allogamous with a rather complex system of sporophytic self-incompatibility controlled by at least 2 multi-allelic S loci. However, artificial self-pollination generally results in some degree of seed set and certain genotypes show a high degree of natural self-fertility.
At physiological maturity (30–40 days after last anthesis) the head becomes yellow, the bracts brown and about 75% of the leaves are desiccated. During the following 10 days the seed will dry to 10–12% moisture content and start shattering, while the receptacle may still contain more than 30% water.
Sunflower is cultivated mainly between 20–55°N and 20–40°S, in relatively cool temperate to warm subtropical climates. In the tropics it can be grown in the drier regions, up to 1500(–2500) m altitude, but sunflower is unsuitable for humid climates. Temperatures for optimum growth are 23–27°C. When grown in hotter climates, oil content is lower and the composition of the oil changes with less linoleic and more oleic acid. Temperatures for germination should not be below 4–6°C and maximum temperatures during growth not above 40°C. Young sunflower plants with 4–6 leaves may withstand short periods of frost down to –5°C. Most sunflower cultivars show day-neutral or quantitative long-day responses to photoperiod. Long photoperiods increase plant height. Water requirement is 300–700 mm during the growing period, depending on cultivar, soil type and climate. More than 1000 mm rain increases the risk of lodging and disease incidence. Sunflower is capable of extracting more soil moisture than most other field crops. Dry weather after seed set is important for adequate ripening of the crop. A wide range of soils from sandy to clayey are suitable for sunflower cultivation, provided they are deep, free draining and not acid; suitable pH ranges from 5.7 to 8.1. The tolerance of sunflower of saline soils is only slightly better than that of soya bean and comparable to that of wheat.
Propagation and planting
Sunflower is sown directly in the field at a depth of 3–8 cm. It requires a medium fine seedbed that is free from weeds. The 1000-seed weight is 40–60 g for oilseed and 80–110 g for non-oilseed cultivars. With mechanical planting seed rates are 3–8 kg/ha depending on seed size and spacing (60–75 cm between rows and 20–30 cm within rows). Optimum final plant densities vary with environment and cultivar: 15,000–30,000 plants/ha for rainfed and 40, 000–60,000 for irrigated sunflower crops. With good seed quality, seedling emergence of more than 80% can be attained. Sunflower has some ability to compensate for lower densities or irregular crop stands by increasing total biomass, seed size and number of seeds per plant, provided other growth factors such as moisture and nutrients are not limiting.
Smallholders often intercrop sunflower with groundnut, pulses and millets, plant it on banks around irrigated fields, or use it as living supports for beans and gourds.
Sunflower seedlings compete poorly with weeds. Control is effected by inter-row cultivation and herbicides. Pre-plant, pre-emergence and post-emergence herbicides are used, but they should be selected carefully as sunflower is extremely susceptible to hormone-based herbicides. Mechanical cultivation should also be done carefully to avoid damage to the extensive superficial network of roots. Irrigation to supplement rainfall to 600–750 mm can result in considerably higher yields in sunflower, but may also increase the risk of lodging, especially for tall cultivars, and in areas where strong winds are common. For this reason too, surface irrigation is the preferred method of application.
Fertilizer requirements depend on yields and nutrient status of the soil. Plant nutrient status can be monitored through foliar analysis by sampling the youngest expanded leaf. Macro-nutrients removed by one t harvested seed are about 25 kg N, 4 kg P, 17 kg K, 2 kg Ca, 3 kg Mg and 2 kg S. Considerable amounts of these elements, K in particular, are also immobilized in the plant stover (stalk and receptacle), resulting in a rather low fertilizer use efficiency. Recommended applications of fertilizer to sunflower crops with expected seed yields of 1.5–2.5 t/ha vary: 50–120 kg N, 20–30 kg P and 40–80 kg K. Seed oil content tends to decline and the protein content to increase with higher N fertilizer applications. Sunflower is particularly susceptible to boron deficiency, which can be rectified by soil or foliar application. Soil application of 1–4 kg B per ha is normally adequate. To avoid a build-up of diseases and pests, sunflower should not be grown in 2 consecutive crops. Crop rotation with cereals and pulses is common.
Diseases and pests
Sunflower is host to more than 30 pathogens, about half of them of worldwide importance and regularly causing considerable economic losses. Probably the most serious crop limiting disease is sclerotinia wilt or white rot caused by Sclerotinia sclerotiorum, which affects roots, stems, buds and heads. Wide host range and longevity of the sclerotia complicate control, but clean seed, wide crop rotation (3–4 years) with non-host crops and the use of less susceptible cultivars help to reduce disease incidence. Equally common fungal diseases are: red rust (Puccinia helianthi) forming small dark brown pustules on the underside of the leaves, eventually causing the leaves to turn brown and in severe cases the death of the plant; alternaria blight (Alternaria helianthi and related species) causing seedling blight, leaf and stem spots and head rot; and septoria leaf spot (Septoria helianthi). Downy mildew (Plasmopara halstedii), causing damping-off in seedlings and yellowing of the leaves that spreads from the midribs and a characteristic upright orientation of the head, is of less importance in eastern and southern Africa than in Europe; it occurs especially in traditional open-pollinated cultivars. Occasionally serious fungal diseases occur, including powdery mildew (e.g. Erysiphe cichoracearum), wilt caused by Verticillium dahliae, charcoal rot (Macrophomina phaseolina), southern blight or collar rot (Sclerotium rolfsii) in warm climates, head rot (Botrytis cinerea) in cool and wet conditions, and white rust (Albugo tragopogonis). Some of these diseases can be controlled by fungicides or by host resistance. A bacterial foliar disease is caused by Pseudomonas syringae and sunflower may also become infected by virus diseases (sunflower mosaic virus (SuMV) and tobacco leaf curl virus (TLCV)) and attacked by nematodes (e.g. Meloidogyne spp., Rotylenchus spp.).
There are numerous insect pests, many of them specific to a continent, the most damaging being those attacking buds, flower heads and developing seeds. A major cause of poor emergence and plant stands are the larvae of various cutworms (Agrotis spp.), wireworms (Gonocephalum spp.) and mole crickets (Gryllotalpa spp.). Other important sunflower pests in Africa are scarabs (Schizonycha spp.), grasshoppers (Zonocerus spp.), leafworm (Spodoptera spp.), leaf miners (Liriomyza spp.) and sucking insects such as Aphis gossypii and Bemisia tabaci, stem borer (Heteronychus spp.), head and developing seed-damaging bollworm (Helicoverpa armigera), sunflower moth (Homoeosoma spp.), blue bug (Calidea spp.) and shield bug (Nezara viridula). Insecticides used to control pests in sunflower should not be toxic to pollinating bees during the flowering period. Crop rotation, trap crops, biological control and host resistance in cultivars are some means of control. Cultivars with seed having a phytomelanin layer in the pericarp are less attacked by seed damaging insect pests. Drooping broomrape (Orobanche cernua Loefl.) is a parasitic plant that feeds on sunflower roots and may cause considerable damage. Broomrape is difficult to control, but integration of a biocontrol agent with a resistance-inducing chemical offers new perspectives. Birds and rodents can cause major losses to the maturing sunflower crop and need control measures (e.g. chemical repellent, scare guns and early harvesting).
Sunflower is ready for harvesting when the heads have turned yellow-brown and seed moisture content is 10–12%, about 120–160 days after planting for tall and 80–110 days for short cultivars. Manual harvesting, as applied by smallholders, involves cutting of the heads and drying them on platforms or threshing floors for 6–7 days in the sun before manual or mechanical threshing and winnowing. Cleaned seeds are dried in the sun again for a few days before storage. The highly uniform ripening of short-stature hybrids allows mechanized harvesting by adapted combine harvesters. Time of harvesting is then usually earlier, when seed moisture is about 20%, to avoid yield losses due to seed shattering during harvesting operations. Before storage, harvested seeds are cleaned and dried to 8% in open sacks under shelter in warm and dry weather, or otherwise by artificial dryers.
World average seed yield is 1.2 t/ha. National averages in Africa range from 0.4 t to 1.3 t/ha, e.g. Tanzania 0.4 t, Zambia, 0.6 t, Sudan 0.8 t, Kenya 1.0 t and South Africa 1.3 t per ha. High yields of 2–4 t/ha (1–2 t/ha of oil) are obtained in Europe and the United States from modern hybrid cultivars and with high inputs. Maximum seed yields of 5–6 t/ha have been obtained in field experiments.
Handling after harvest
Small quantities of dried seed can be stored in moisture- and insect-proof containers placed in a cool place. Large-scale storage of sunflower seeds requires well-aerated bins or silos to maintain seed moisture content at about 8%. Regular inspection prior to and during storage is necessary to avoid storage insect pests similar to those in other grain crops. Infestations may be controlled by fumigation.
The extraction and processing of oil takes place in oilseed crushing plants. The seed is first cleaned and dried to 7% moisture content before being hulled (decortication), which involves cracking and separation of the fruit wall. Three methods of industrial oil extraction are available: mechanical expulsion by screw press, organic solvent extraction e.g. with hexane, or a combination of mechanical and solvent extraction. Mechanical pressing leaves a meal residue with 5–6% oil, while solvent extraction forms residues with 0.5–1.5% oil. The crude oil is subsequently cleaned by filtration, refined (chemically or by steam) to reduce its free fatty acid content, bleached (with bleaching earth) to remove carotenoids and other pigments, and finally deodorized (stripping by steam) to produce a colourless cooking and salad oil. Oil stability is improved by adding anti-oxidants. The manufacturing of margarine requires an additional process of partial hydrogenation of the sunflower oil and usually blending with other vegetable oils to produce the right hardness and mouthfeel.
Most wild Helianthus species are potentially useful genetic resources for the improvement of the cultivated sunflower because of the relative ease of introgression by interspecific hybridization. Embryo-rescue and in-vitro culturing are quite successful methods of achieving difficult interspecific hybridization in sunflower. Wild Helianthus annuus and several other species have contributed important characters for the improvement of the cultivated sunflower, such as (nuclear and cytoplasmic) male sterility, fertility restoration, resistance to several diseases and some pests, improved drought and salt tolerance as well as changed fatty acid composition.
Large collections of germplasm of sunflower and wild Helianthus spp. are maintained by the Institute of Crop Science (CAAS), Beijing, China (2250 accessions), INRA, Montpellier, France (2500 accessions), the National Institute of Information and Documentation, Bucharest, Romania (1125 accessions), the N.I. Vavilov Scientific Research Institute of Plant Industry (VIR) in St.Petersburg, Russian Federation (3055 accessions), the Research Institute for Field and Vegetable Crops at Novi Sad, Serbia and Montenegro (5150 accessions), and the USDA North Central Regional Plant Introduction Station, Ames IA, United States (3814 accessions, of which more than 1000 wild Helianthus).
Uniform F1 hybrids have almost completely replaced the open-pollinated cultivars developed by mass and family selection such as ‘Peredovik’ in Russia (released in 1930). The early hybrid cultivars based on self-incompatibility like ‘Advance’ in Canada (1946) or on nuclear male sterility like ‘INRA 651’ in France (1969) still had 30–50% selfed plants. The discovery of cytoplasmic male sterility (CMS) in offspring of an interspecific cross of Helianthus petiolaris Nutt. × Helianthus annuus together with maintainer and restorer genes in France in 1968–1970 quickly led to a new generation of sunflower F1 hybrids with the potential of maximally exploiting hybrid vigour: no selfed plants and 100–150% higher yields than open-pollinated cultivars. In the meantime more than 70 new sources of CMS have been detected within the Helianthus gene pool, but most of the F1 hybrids grown at present are still based on the first CMS source, partly because introgression into inbred lines and finding matching restorer genes takes time. Selection against self-incompatibility during inbred line development leads to self-fertile F1 hybrids capable of good seed production even when pollinating insects are less abundant. Multi-branched male lines are commonly used to enhance pollination and seed set in large-scale seed production. This character is conditioned by one recessive gene and the F1 hybrids will be unbranched.
Breeding objectives include higher yield and oil content, precocity, reduced plant height and higher harvest index. There is generally a positive correlation between seed yield, plant height, head diameter and single seed weight, while oil content is negatively correlated with pericarp thickness. Other objectives are resistance to diseases and pests, drought, low temperatures, salinity and lodging. Many sunflower hybrids are resistant to downy mildew (Plasmopara halstedii) and rust (Puccinia helianthi), both conditioned by dominant major genes, but the resistances are race-specific and breakdowns due to new virulent races of the pathogen have occurred. Resistance to sclerotinia wilt or white rot (Sclerotinia sclerotiorum) is difficult to achieve due to its complexity and polygenic inheritance. Broomrape resistance exists, but here also virulent races may overcome this. Bird damage appears to be less in sunflowers with concave-shaped heads which hang parallel to the soil at plant maturity.
There is still considerable scope for increasing yields in sunflower, although the upper limits of selection for higher oil content may not be far above 60%. Further exploitation of the considerable genetic resources present in the wild Helianthus gene pool should contribute to higher crop security by improved resistance to diseases and pests, which at present still account for the destruction of 40–50% of the world sunflower crop. Recent advances in sunflower biotechnology, like marker assisted selection and genetic transformation, are expected to contribute considerably to more efficient sunflower improvement, in particular where conventional breeding has failed to produce results. For example, significant progress has been made already in developing transgenic sunflower with partial resistance to Sclerotinia sclerotiorum, based on the expression of a gene that detoxifies the oxalic acid secreted by the invading pathogen.
Sunflower produces an excellent vegetable oil, but expansion beyond the highlands of eastern and southern tropical Africa will be difficult because it is unsuitable for hot and humid climates. Numerous diseases and pests, as well as serious risks of damage by birds and rodents are also limiting factors to small-scale and low-input cultivation of this crop.
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Correct citation of this article
van der Vossen, H.A.M. & Fagbayide, J.A., 2007. Helianthus annuus L. [Internet] Record from PROTA4U. van der Vossen, H.A.M. & Mkamilo, G.S. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 16 February 2021.
- See the Prota4U database.