Helianthus annuus (PROSEA)
- Protologue: Sp. pl.: 904 (1753).
- Family: Compositae
- Chromosome number: 2n= 34
- Sunflower (En).
- Tournesol (Fr)
- Indonesia: bunga matahari (Indonesian), kembang sarengenge (Sundanese), purba negara (Javanese)
- Malaysia: bunga matahari
- Philippines: mirasol (Pilipino, Tagalog), lampao (Ifugao), ak-aklit (Bontok), takin-takin (Hanunuo)
- Thailand: thantawan (general), bua-thong (northern)
- Vietnam: hướng dương.
Origin and geographic distribution
Wild H. annuus spread from its origin in the south-western United States to most regions of North America, partly naturally and partly in association with human migration in prehistoric times. According to archaeological evidence modern single-headed sunflowers are derived from similar 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 a source of oil. Sunflower became popular in Europe as a novel ornamental soon after its first arrival in the botanic garden of Madrid around 1510 from Mexico. Its potential as an oilseed crop for higher latitudes became apparent in 18th Century 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 Russia developed high-yielding and oil-rich sunflower cultivars, which played a crucial role in the expansion of sunflower production in Europe and elsewhere in the world between 1920 and 1970. Modern sunflower production in North and South America (mainly 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 F1hybrid seed technology in combination with dwarf and semi-dwarf plant habits, high oil content of the seed and resistance to diseases and pests have been major factors leading to the spectacular increase of sunflower production since 1980 in Argentina, India, China, Turkey and the European Union (e.g. France, Spain and Italy). Sunflower production in South-East Asia is a recent development with Burma (Myanmar) and Thailand being the main producers.
Sunflower seed yields an edible oil of excellent quality due to a high concentration of unsaturated fatty acids, near absence of toxic substances, attractive light colour, good taste and flavour. It 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 soya bean and 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 is a protein-rich meal used as livestock feed. For this purpose, it is commonly blended with soya bean 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. The indigenous people of North America have had a long tradition of preparing bread-like products from ground sunflower seeds.
The seeds (achenes) of non-oil cultivars which are large and often black and white-striped, are consumed directly. Generally, the largest 25% of the seeds are consumed as salted and roasted snacks, the medium 30-50% fraction is used as hulled seeds in confectionery and bakery products and the smallest seeds as birdseed and pet food.
Sunflower is sometimes cultivated as a forage crop. It requires a shorter growing season, is more drought tolerant and produces a silage only slightly inferior to maize (Zea mays L.). In Russia and Canada, sunflower is occasionally grown as a hedge crop in fields of wheat to accumulate snow and to protect against desiccating winds. Sunflower is also grown as an ornamental garden and pot plant.
Formerly, yellow and purple dyes were extracted from the florets.
Production and international trade
Average annual world production of sunflower seed over the period 1994-1998 was about 24 million t, equivalent to 9 million t oil, from 21 million ha in 58 countries. Argentina is the largest producer (5.5 million t), followed by the Russian Federation (3 million t), Ukraine (2.2 million t), United States (2 million t), France (1.9 million t), India (1.5 million t), China (1.2 million t), Spain (1.1 million t), Romania (1 million t), Turkey (850 000 t) and Hungary (700 000 t). Countries in South-East Asia with sizable sunflower production are Burma (Myanmar) (130 000 t) and Thailand (20 000 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, 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 oilseed sunflower production. Most of it is traded in the domestic markets, except for 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 seeds (achenes) is approximately: water 5-7 g, protein 14-25 g, oil 20-60 g, other lipids 1-2 g, carbohydrates 18-27 g and ash 2-4 g. Oilseed sunflower cultivars have a high oil content (more than 50%) and low hull fraction (20-25%), against the low oil content (25-30%) and high hull fraction (43-52%) of non-oilseed sunflower cultivars. About 97-98% of 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%, 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 1-2 mg/kg carotenoids (provitamin A) and 630-700 mg/kg tocopherols (fat-soluble vitamin E).
Sunflower meal has a protein content of 28-45% depending on cultivar and method of oil extraction and is a good source of Ca, P, K and vitamin B complex. Sunflower proteins are easily digestible and have a high biological value, but are somewhat deficient in the essential amino acid lysine. The 1000-seed (achene) weight is 40-60 g for oilseed and 80-110 g for non-oilseed cultivars.
- A variable, erect, hirsute, annual herb, usually 2-4 m tall. Taproot strong, up to 2-3 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 head in mature plants, (0.5-)1.6-1.8(-5) m tall, round with ridges, 3-6 cm in diameter, branched in many wild forms, unbranched in most cultivated forms, woody and angular at maturity and often becoming hollow.
- Leaves cordate and opposite below, higher ones soon becoming ovate and alternate in spiral with two-fifths phyllotaxis, 20-40 per plant; petiole long; blade cordate to ovate, 10-30 cm × 5-20 cm, margin serrate, apex acute or acuminate, hispid on both sides with glandular and non-glandular trichomes, veins prominent and forming a reticulate pattern.
- Inflorescence a terminal head (capitulum), 10-50 cm in diameter, sometimes drooping; receptacle flat to concave or convex, 1-4 cm thick; involucral bracts arranged in 3 rows, ovate to ovate-lanceolate, ciliate; outer ring of flowers are sterile but showy ray florets, deciduous, corolla ligulate, elliptical, about 6 cm × 2 cm, strongly 2-veined, yellow, sometimes white, lemon, orange or red; inner flowers are bisexual disc florets, arranged in spiral whorls from the centre of the head, 700-3000 in oilseed types, up to 8000 in non-oilseed types per head, about 2 cm long, subtended by a pointed bract; 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, with single basal ovule, style long with nectaries at its base, stigma with 2 curved lobes.
- Fruit an achene (in sunflower commonly called "seed"), obovoid, flattened, slightly 4-angled with truncated tip and rounded base, variable in size and colour, 7-25 mm × 4-15 mm × 3-8 mm, white, cream, brown, purple, black, or white-grey with black stripes, sometimes with phytomelanin layer.
- Seed (kernel) with thin seed coat adnate to the fruit wall (hull), a single layer of endosperm and a large straight embryo which for the major part consists of the 2 cotyledons.
- Seedling with epigeal germination.
Growth and development
Sunflower seeds show dormancy until 30-50 days after harvesting, but this is easily overcome by rinsing them 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. 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 honey-bees and bumble-bees. 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 the head becomes yellow, the bracts brown and about 75% of the leaves are desiccated. During the following 10 days, the seeds will dry to 10-12% moisture content and start shattering, while the receptacle may still contain more than 30% water.
Other botanical information
At present, the genus Helianthus L. comprises about 50 species, including annual and perennial, diploid as well as polyploid species, all endemic to North America. H. annuus L. is one of the 13 annual species. It is a complex species, comprising wild and cultivated sunflowers, formerly classified as subsp. lenticularis (Dougl.) Cockerell and subsp. annuus respectively. Within subsp. annuus two groups were distinguished, a weedy group (var. annuus) and the cultivated sunflowers group (var. macrocarpum (DC.) Cockerell). Cultivated sunflowers, however, can better be classified into cultivar groups and cultivars, but such a classification does not yet exist. Four groups of sunflower cultivars can be distinguished according to plant height:
- Tall (Giant) cultivars: 2-4 m, late maturing; heads 30-50 cm in diameter; seeds large, white or grey or with black stripes; oil content rather low; representative: "Mammoth Russian", an old, very tall cultivar;
- Standard cultivars: 1.5-2.1 m; representatives: "Peredovik", "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, seeds black, grey or striped; oil content higher than in tall cultivars; representatives: "Pole Star", "Jupiter", most modern hybrid cultivars;
- Dwarf cultivars: 0.8-1.2 m, early maturing; fewer nodes and leaves than standard cultivars but normal internode length; flower heads 13-17 cm in diameter; seeds small; highest oil content; representatives: "Advance", "Sunrise".
Sunflower is cultivated mainly between 20-50°N and 20-40°S, in relatively cool temperate to warm subtropical climates. In the tropics, it can be grown in 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 composition changes with less linoleic acid 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, but there is at least one short-day cultivar. Long photoperiods increase plant height. Water requirement is 300-700 mm during the main 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 neither acid nor saline; suitable pH ranges from 5.7 to 8.1.
Propagation and planting
Sunflower is sown directly in the field at a depth of 3-8 cm. It requires a medium fine seed-bed that is free from weeds. With mechanical planting, seed rates are 3-8 kg/ha depending on seed size and spacing. Commonly used spacings are 60-75 cm between rows and 20-30 cm within the row. Optimum final plant densities vary with environment and cultivar: 15 000-30 000 plants/ha under 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 groundnuts, pulses and millets, plant it on banks around irrigated fields, or use it as living support for beans and gourds.
Sunflower seedlings compete poorly with weeds. Control is effected by interrow 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 1 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 particularly, are also immobilized in the plant stover, resulting in a rather low fertilizer use efficiency. Recommended applications of fertilizer to sunflower crops with expected yields of 1.5-2.5 t seeds per ha vary: 50-120 kg N, 20-30 kg P and 40-80 kg K. 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. Sunflower should not be grown in 2 consecutive crops to avoid a build-up of diseases and pests. Crop rotation with cereals and pulses is common.
Diseases and pests
Sunflower is affected by some 15 pathogens of worldwide importance, regularly causing considerable economic losses. Probably the most serious 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. Other major fungal diseases and pathogens are: downy mildew (Plasmopara halstedii) causing damping-off in seedlings and yellowing of the leaves that spreads from the midribs, downy growth underneath the leaves and a characteristic upright orientation of the head; sunflower 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) causing lesions in the leaves. Sunflower can be a host of the cucumber mosaic virus (CMV) and Mormor astrictum which infect tobacco crops in East Java, Indonesia. Sunflower is also attacked by nematodes, e.g. Meloidogyne and Rotylenchus species. There are numerous insect pests, many of them specific to a continent, but the most damaging are those that attack buds, flower heads and developing seeds. A major cause of poor emergence and plant stands are the larvae of various cutworms (Agrotis spp.), wireworms (Gonocaephalum spp.) and crickets (Gryllotalpa spp.). Other important sunflower pests in Asia are: Chrotogonus spp., Diacrisia spp., Spilosoma spp., Spodoptera spp., the leaf miner Phytomyza atricornis and sucking insects like Aphis gossypii and Bemisia tabaci on foliage; stem borer Ostrinia damoalis ; and Helicoverpa armigera, Homoeosoma nebulella, Oxycertonia spp. and Dolycoris indicus on the head and developing seeds. Insecticides to control pests in sunflower should not be toxic to pollinating bees during the flowering period. Cultivars with seeds that have a phytomelanin layer in the pericarp are less attacked by seed-damaging insect pests. Birds and rodents can cause major losses to the maturing sunflower crop and can be controlled by measures such as scaring, chemical repellents and early harvesting. Broomrape (Orobanche cernua Loefl.) is a plant parasite that feeds on the roots and may cause considerable damage also in Asia. Crop rotation, catch crops, biological control and resistant cultivars are means of control. Sunflower affects germination of witchweed (Striga spp.), but is not a host and may contribute to its control. In some states of the United States, weedy sunflower forms are considered noxious weeds.
Sunflower is ready for harvesting when the heads have turned yellow-brown and seed moisture content is 10-12% at about 120-160 days after planting for tall and 80-110 days for dwarf cultivars. Manual harvesting by smallholders involves cutting 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 shattering. Before storage, harvested seeds are cleaned and dried to 8% moisture content in open sacks under a shelter in warm and dry weather, or otherwise by artificial dryers.
World average seed yield is 1.2 t per ha. National averages range from 0.5 t-2.5 t, e.g. India 0.7 t, Burma (Myanmar) 0.8 t and China 1.5 t per ha. High yields of 2-4 t per ha are obtained in France and the United States from modern hybrid cultivars and with high inputs. Maximum yields of 5-6 t seed per ha have been obtained in field experiments.
Handling after harvest
Small quantities of dried seeds can be stored in moisture-proof and insect-proof containers placed in a cool place. Large-scale storage of sunflower seeds requires well-aerated bins or silos maintained at low relative humidity. Regular inspection prior to and during storage is necessary to avoid storage 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 cracking and separating the pericarp from the seeds. Three methods of oil extraction are available: expulsion by mechanical 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 only 0.5-1.5 % oil. The crude oil is subsequently cleaned by filtration, refined to reduce its free fatty acid content, bleached to remove carotenoids and other pigments and finally deodorized 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 culture is quite a successful method for achieving difficult interspecific hybridization in sunflower. Wild H. annuus and several other species have been important sources of resistance to several diseases and some pests, cytoplasmic male sterility and other agronomic characters such as drought and salt tolerance. The USDA’s North Central Regional Plant Introduction Station at Ames, Iowa, has the largest germplasm collection with 3300 accessions of which 2245 are wild species. Other research centres with important Helianthus germplasm collections are the N.I. Vavilov Institute (VIR) at St. Petersburg and the Research Institute for Oil-bearing Crops (VNIIMK) at Krasnodar, both in Russia; the Plant Breeding Station in Clermont-Ferrand, France; the Research Institute for Field and Vegetable crops in Novi Sad, Yugoslavia; and the Research Institute for Cereals and Industrial Crops in Fundulea, Romania.
Uniform F1hybrids have almost completely replaced the open-pollinated cultivars developed by mass and family selection such as "Peredovik" in Russia. The early hybrid cultivars based on self-incompatibility like "Advance" in Canada or on genetic male sterility like "INRA 651" in France still had 30-50% selfed plants. The discovery of cytoplasmic male sterility in offspring of an interspecific cross of H. petiolaris × H. annuus together with maintainer and restorer genes in France in 1968-1970 quickly led to a new generation of sunflower F1hybrids. Potential yields are 100-150% higher than those of open-pollinated cultivars. In the meantime more than 40 new sources of CMS have been detected within the Helianthus gene pool, but most of the F1hybrids 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 F1hybrids capable of producing good seed when pollinating insects are less abundant. Multi-branched male lines are used to enhance pollination and seed set in large-scale seed production. This character is conditioned by one recessive gene and the F1hybrids will be unbranched.
Breeding objectives include higher yield and oil content, precocity, reduced plant height and higher harvest index. Generally, seed yield is positively correlated with 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 (Plasmopora halstedii) and rust (Puccinia helianthi) which are 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 and rot are difficult to achieve due to its complexity and polygenic inheritance. Broomrape resistance exists, but virulent races may overcome it. Bird damage appears to be less in cultivars with concave-shaped heads which hang parallel to the soil at 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 wild Helianthus gene pool should contribute to higher crop security by improved host resistance to diseases and pests, which at present still account for the destruction of 40-50% of the world sunflower crop. In recent years sufficient progress in molecular marker-assisted selection and genetic transformation has been made in sunflower to expect substantial contributions to more efficient improvement from these advanced technologies.
Sunflower produces an excellent vegetable oil, but possibilities for expansion in South-East Asia are limited to drier parts. Numerous diseases and pests, as well as serious risks of damage by birds and rodents are also factors limiting the possibilities for small-scale and low-input cultivation of this crop.
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H.A.M. van der Vossen & Soonthorn Duriyaprapan