Helianthus

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Helianthus

(hē'lēăn`thəs): see sunflowersunflower,
any plant of the genus Helianthus of the family Asteraceae (aster family), annual or perennial herbs native to the New World and common throughout the United States.
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Helianthus

 

(sunflower), a genus of plants of the family Compositae. Approximately 50 herbaceous species grow in North America, and 28 species, mainly subshrubs, are encountered in Mexico and Peru. Most sunflower species are perennials. Of the annuals, the common sunflower (H. annuus) is cultivated, and of the perennials, the girasole (H. tuberosus). H. lenticularis is found as a weed in the corn belt of the United States (Iowa, Illinois, Indiana), in southern Canada, in northern Mexico, and in the southeastern USSR. Species used as ornamentals include the cucumber-leaf sunflower (H. cucumerifolius) and the silver-leaf sunflower (H. argophyllus).

The rachidian root system of the common sunflower extends 2–3 m into the soil, allowing the plant to obtain moisture from the deep layers. The erect stem reaches 5 m in height (for oil-bearing varieties, 0.6–2.5 m) and is sparsely covered with stiff hairs. The large, pubescent, ovate-cordate leaves have acuminate tips and are on long petioles. The inflorescence is a head measuring 15–20 cm across. It is surrounded by involucral bracts. The ligulate ray flowers are sterile, and the tubular disk flowers are bisexual and form the seeds. The corolla varies in color from light yellow to dark orange; sometimes it is violet. The sunflower is cross-pollinated by bees and other insects and by the wind. The elongate fruit is a wedge-shaped achene consisting of a pericarp and a white seed covered by a seed coat. In the pericarp of modern varieties, between the sclerenchyma and the cork tissue, is an “armored” layer, which protects the achenes from the destructive sunflower moth. The various varieties of H. annuus are divided according to morphological characteristics into varieties raised for food, for oil, and for both food and oil. The achenes of oil varieties are dark gray with light stripes, coal black, or, less commonly, gray with stripes; achenes used for food are gray with stripes or, less frequently, white.

The vegetative period is between 80 and 140 days. For the appearance of normal sprouts—on the 13th or 14th day—the average daily soil temperature at the planting depth must be 14°–15°C. The plant requires higher temperatures, 18° to 26°C, as it develops between sprouting and flowering, and sunny weather is necessary. The sprouts can tolerate brief night frosts from—6° to—8°C. The sunflower uses considerable amounts of moisture and nutrients for transpiration. To produce 1 quintal of seed, the plant requires 170–180 tons of water, 4.5 kg N, 1.8 kg P2O5, and 8.9 kg K2O. The water supply during active growth (prior to flowering) and during seed formation and ripening largely determines the size and quality of the harvest. With sufficient water reserves in the soil, the plant can tolerate a drought with relative ease. The best soils for growing sunflowers are chernozems, which have high water capacity and air and water permeability.

The achenes have an oil content of 29 to 57 percent. Oil cakes and oil-seed meal made from the achenes provide a high-protein concentrated feed. Cattle readily eat the threshed heads, chaff, and silage from plants harvested during blooming. The sunflower yields a substantial amount of nectar.

The wild sunflower was imported from North America into Europe by the Spanish in 1510. It was cultivated as an ornamental and kitchen-garden plant. Large-seeded varieties were produced from the wild varieties by careful selection; from them were developed the varieties used in the production of oil. In the 18th century the sunflower was imported into Russia from the Netherlands. It was first introduced into cultivation in Russia by D. S. Bokarev, a serf from the village of Alekseevka in Biriuch District, Voronezh Province. In 1829 he obtained oil from the seeds; in 1833 the first oil mill was built in Alekseevka. By the mid-19th century the sunflower occupied between 30 and 40 percent of the land under cultivation in many parts of Voronezh and Saratov provinces. Later the area under sunflower cultivation decreased because of the extensive spread of diseases and pests. Only the development through selection of the Zelenka variety, which is resistant to rust, and of “armored” varieties permitted large areas to once again be planted with sunflowers (980,000 hectares [ha] in 1913). In the 19th century, cultivated oil-bearing varieties were imported from Russia into the United States and Canada.

In 1950 worldwide plantings of sunflowers totaled 7.1 million ha; in 1960, 7.5 million; in 1970, 8.5 million; and in 1972, 8.8 million, including 1.3 million in Argentina, 560,000 in Rumania, 450,000 in Turkey, 320,000 in Australia, and 300,000 in Spain. The gross seed harvest in 1971 was 9.45 million tons, with an average yield of 10.7 quintals per ha (6.5 in Argentina, 14.3 in Rumania, 12.7 in Turkey, 4.4 in Australia, and 8.2 in Spain).

In 1940 the area under sunflower cultivation in the USSR totaled 3.54 million ha; in 1960, 4.19 million; in 1970, 4.78 million; and in 1973, 4.75 million. For these same years, the gross seed harvest, in millions of tons, was, respectively, 2.64, 3.97, 6.14, and 7.39; the average yields were 7.4, 9.4, 12.8, and 15.5 quintals per ha. The principal sunflower-growing regions are the RSFSR (Northern Caucasus, Central Chernozem Region, Volga Region), the Ukraine, Moldavia, and Kazakhstan.

In the USSR, oil-rich, thin-shelled (no more than 27 percent), broomrape-hardy varieties resistant to rust and the sunflower moth have been developed (crustification, 97–98 percent). The work of the Soviet selectors V. S. Pustovoit, L. A. Zhdanov, and others has resulted in a dramatic increase in the average oil content of the seeds and the yield of oil from 28.6 and 25.15 percent, respectively, in 1940 to 48.4 and 40.3 percent in 1973. Selection work is continuing in the development of more productive varieties possessing group immunity to diseases. In 1974 in the USSR, 26 varieties were regionalized. The most extensive areas (more than 1.2 million ha each) are occupied by the Peredovik and Armavirskii 3497 varieties.

In crop rotations, sunflowers are planted after cereals (wheat), corn, and other plants that do not use moisture from the deep soil layers. The main tilling of the soil is done in the autumn (shallow plowing, plowing, or deep cultivation). In the spring, presowing cultivation usually takes place only once; weedy fields undergo additional early cultivation with harrowing. Shortly before plowing, manure (20 tons per ha) and mineral fertilizers are applied. The rate of fertilization is 40 kg N per ha, 60–90 kg P2O5 per ha, and on sandy-loam soils, 40–60 kg K2O per ha.

In the principal sunflower-growing zones, sowing takes place when the soil has warmed up from 8° to 12°C. The methods of sowing are wide-row, square (in weedy fields), and drill, with the rows spaced 70 and 90 cm apart. Between 20,000 and 50,000 plants are raised per ha; as many as 60,000 are grown on irrigated land. The planting depth is 6–10 cm. Herbicides (Prometrin and Treflan) are applied to the soil during sowing. Crop maintenance includes harrowing and one or two cultivations to loosen the soil and remove weeds. The plants are generally pollinated by bees.

Sunflowers are harvested when most of the head (80–90 percent) becomes yellow-brown and brown and the moisture content of the seeds is 12–17 percent. Desiccation of the crops with magnesium chlorate lowers the moisture content of the seeds to 10–12 percent, thus making it possible to harvest the plants five to seven days earlier than usual.

The soil is prepared for planting by general-purpose machines, such as plows, harrows, and cultivators. Sowing is done with corn planters, and the plants are harvested with grain combines having attachments for harvesting sunflowers. Sunflower pests include wireworms, false wireworms, the sunflower moth, and caterpillars of various species of the genus Agrotis. Diseases include sclerotiniose, gray mold, and broomrape parasitosis.

REFERENCES

Glubokov, T. P. Mnogoletnie podsolnechniki. [Saratov] 1946.
Zhdanov, L. A., R. M. Bartsinskii, and I. F. Liashchenko. Biologiia podsolnechnika. Rostov-on-Don, 1950.
Podsolnechnik, 2nd ed. Moscow, 1965.
Pustovoit, V. S. Izbrannye trudy. Moscow, 1966.
Sinskaia, E. N. Istoricheskaia geografiia kul’turnoi flory. Edited by D. D. Brezhnev. Leningrad, 1969.
Zhukovskii, P. M. Kul’turnye rasteniia i ikh sorodichi, 3rd ed. Leningrad, 1971.

P. G. SEMIKHNENKO