Prota 2: Vegetables/Légumes
Sp. pl. 1: 242 (1753).
2n = 18
Carrot (En). Carotte (Fr). Cenoura (Po). Karoti (Sw).
Origin and geographic distribution
It is generally assumed that the eastern, purple-rooted carrot originated in Afghanistan in the region where the Himalayan and Hindu Kush mountains meet, and that it was domesticated in Afghanistan and adjacent regions of Russia, Iran, India, Pakistan and Anatolia. Purple carrot, together with a yellow variant, spread to the Mediterranean region and western Europe in the 11–14th centuries, and to China, India and Japan in the 14–17th centuries.
The western, orange carrot probably arose in Europe or in the western Mediterranean region through gradual selection within yellow carrot populations. The Dutch landraces Long Orange and the finer Horn types, first described in 1721, were an important basis for the western carrot cultivars grown at present all over the world. They have now largely replaced the eastern types because of superior taste and nutritional value, and can also be found throughout Africa.
The swollen taproot of Daucus carota is an important market vegetable, also in tropical areas. The roots are consumed raw or cooked, alone or in combination with other vegetables, as an ingredient of soups, dishes (e.g. couscous), sauces, juices and in dietary compositions. Large coarse roots are also used as fodder. Young leaves are sometimes eaten raw or used as fodder. In Ethiopia fruits are used against tapeworm. Essential oil extracted from the seed is used for flavouring. Carotene is extracted from the root and used to colour margarines and is added to hen feed to modify egg-yolk colour.
Production and international trade
World carrot production increased from 13 million t in 1992 to 21 million t in 2002. Total area under carrot cultivation in 2002 was about 990,000 ha, with China 370,000 ha, Commonwealth of Independent States (including the Russian Federation) 171,000 ha, European Union 76,000 ha, eastern Europe and the Balkan 58,000 ha, the Americas 104,000 ha and Africa 80,000 ha (including North Africa 38,000 ha). Carrots are widely grown during the dry season in the (semi-)arid zones of West and Central Africa and in the highlands of East and southern Africa. The estimated area in Nigeria is 27,000 ha, in Kenya 5000 ha; statistics are not available for other countries. Occasionally, carrots imported from Europe (Belgium) are found in city markets in West Africa, e.g. in Abidjan (Côte d’Ivoire).
Carrots (orange, young, raw, ends trimmed, edible part 87%) contain per 100 g edible portion: water 88.8 g, energy 126 kJ (30 kcal), protein 0.7 g, fat 0.5 g, carbohydrate 6.0 g, dietary fibre 2.4 g, Ca 34 mg, Mg 9 mg, P 25 mg, Fe 0.4 mg, Zn 0.2 mg, carotene 5.33 mg, thiamin 0.04 mg, riboflavin 0.02 mg, niacin 0.2 mg, folate 28 μg, ascorbic acid 4 mg (Holland, B., Unwin, I.D. & Buss, D.H., 1991). Orange carrot is a rich source of carotenoids (pro-vitamin A).
The colour of eastern, purple carrots is caused by the anthocyanins in the root; in the western orange carrot the anthocyanins are replaced by carotene and carotenoids. Some Japanese cultivars with red flesh are rich in lycopene. Sugars, esters, terpenoids and other volatile compounds influence the flavour of raw carrots. Carrots grown under cool conditions are generally sweeter than those grown under high temperatures. An astringent taste of carrots is caused by a high terpolene content in combination with a low percentage of sugars. The bitter taste of carrots after long storage is caused by the conversion of phenols into isocoumarins (mainly 6-methoxymellein) under the influence of exogenous ethylene. These compounds are often a reason for consumer rejection of carrot products and a major problem for vegetable processors. The seed contains an essential oil with notes comparable to the root. The main components of the oil are the sesquiterpene alcohol carotol, daucol and the sesquiterpene β -bisabolene.
Annual or biennial erect herb up to 50 cm tall at the mature vegetative stage and up to 150 cm tall when flowering; taproot fleshy, straight, conical to cylindrical, 5–50 cm long and 2–5 cm in diameter at top, orange (most common), reddish violet, yellow or white. Leaves in a rosette at base of plant, but alternating on flowering stems, 2–3 -pinnate; stipules absent; petiole long, sheathed at base, petiole and rachis pilose; segments divided into oblong to lanceolate or linear ultimate lobes. Inflorescence a terminal, compound umbel with numerous unequal rays, strongly contracted in fruit; involucral bracts 7–13, pinnatipartite or pinnatisect, with linear lobes. Flowers mainly bisexual, but male flowers present in addition to bisexual flowers, often 1–few dark purple sterile flowers present in the centre of umbel, c. 2 mm in diameter, 5-merous; pedicel 0.5–1.5 cm long; calyx with small teeth or absent; petals free, white or pinkish, often enlarged in exterior flowers of umbel; stamens free; ovary inferior, bristly hairy, 2-celled, styles 2. Fruit an oblong-ovoid schizocarp 2–4 mm long, at maturity splitting into two 1-seeded mericarps, primary ridges ciliate, secondary ridges with hooked spines. Seedling with epigeal germination; taproot long, thin; hypocotyl 0.5–1.5 cm long, epicotyl absent; cotyledons linear, leafy; first true leaves pinnate.
Other botanical information
Daucus comprises about 20 species occurring mainly in the Mediterranean region. Wild Daucus carota is widespread in Europe and western Asia, and occurs also in northern Africa (Morocco, Algeria, Tunisia) and locally in tropical Africa (Eritrea, Ethiopia), at higher altitudes. Elsewhere in tropical Africa it is occasionally naturalized after escape from cultivation; this is also the case in other parts of the world, e.g. in North America, where it is now locally a common and noxious weed.
Daucus carota is a complex, very variable species. The complex has been subdivided into a dozen subspecies, 1 of these for cultivated carrot (subsp. sativus (Hoffm.) Arc.). However, for cultivated taxa it is better to classify into cultivar groups directly below the species level. There are two main groups of cultivated carrot, based on root and leaf morphology:
– The eastern (anthocyanin) carrot: root branched, yellow, reddish-purple to purple-black, rarely yellowish-orange; leaves slightly dissected, greyish-green, pubescent; flowering in the first year.
– The western (carotene) carrot: root unbranched, yellow, orange or red, occasionally white; leaves strongly dissected, bright green, sparsely hairy; normally biennial, but often annual in tropical regions.
At present the western carrot is by far the most important, although the eastern carrot is still cultivated in some Asian countries. Three main groups of western (carotene) carrot cultivars arose by selection in the 19th and early 20th centuries in Europe and the United States:
– Early Short: 3–8 cm long globular-shaped roots, fine foliage; cultivars include ‘Grelot’, ‘French Forcing’, ‘Parisian Market’.
– Early Half-Long: 10–20 cm long cylindrical to conical roots, fine to medium foliage; cultivars include ‘Amsterdam Forcing’, ‘Nantes’, ‘Vertou’, ‘Touchon’, ‘Sitan’.
– Late Half-Long: 12–25 cm long conical and shouldered, stump or pointed roots, medium to large foliage, productive; cultivar types include ‘Chantenay’ (short), ‘Royal Chantenay’ (long), ‘Danver’, ‘Autumn King’, ‘Berlicum’ and ‘Imperator’. ‘Kuroda’, developed around 1950, also belongs to this group; it combines an orange internal colour with heat tolerance.
In all groups many open-pollinated and F1-hybrid cultivars have been developed, mostly by private seed companies in Europe, the United States and Japan. The majority of carrot cultivars are bred for temperate climates. When grown under hot conditions, these are less productive, often more affected by diseases and have poorer internal colour than cultivars developed especially for warm climates, e.g. ‘Kuroda’, ‘Brasilia’, ‘Tropical Nantes’ and some local selections in Africa and Asia. Popular cultivars in Africa are ‘Nantes’, ‘Chantenay’ and ‘Kuroda’. In the Kenyan highlands cultivars producing baby carrots (e.g. ‘Minicor’, ‘Orange Finger’ and ‘Sucrum’) are produced for the export market.
Cultivated carrot crosses readily with wild carrot, which occurs naturally in Europe, western Asia and northern Africa, and which is naturalized in other regions, e.g. North America. Wild carrot has to be rigorously removed from seed production fields to prevent white -rooted and prematurely bolting plants in a carrot crop (white roots and annual habit are dominant over orange roots and biennial habit). Most other wild Daucus species are crossable with the cultivated carrot.
Growth and development
Carrot seed will remain viable (70–80% germination) for 6–7 years when stored dry (moisture content 9%) at temperatures below 18°C. First appearance of seedlings is 9–12 days after sowing. The first 4 true leaves are formed at 4–5-day intervals, starting 3–4 weeks after sowing; for subsequent leaves the interval increases gradually to 15–18 days. A thin taproot grows down vertically to 20–25 cm, and 30–40 days after germination it starts swelling and gradually turning orange (in carotene carrots) from the hypocotyl part of the stem downwards. About 80% of all carbohydrates produced in the plant are diverted to the root during this stage of development.
The roots are mature 60–120 days after sowing according to the type of cultivar and growing conditions. The generative phase is induced by low temperatures. Carrot plants become sensitive to vernalization after the formation of at least 8 leaves. The bolting -resistant cultivars of higher latitudes require 5–12 weeks at 2–6°C to induce bolting. Local cultivars grown in the tropics show bolting when the night temperatures drop below 16°C. When flower induction has taken place the generative phase is accelerated by long days. First a new rosette of leaves is formed followed by elongation of the flowering stalk and first flowering 3 months later. Flowering may last for one month, starting with the primary umbel.
Carrot is predominantly outbreeding due to protandry. Insects such as bees and flies, attracted by abundant nectar, effect cross-pollination. The stigma becomes receptive 2–3 days after pollen dehiscence. Petals drop soon after fertilization and the fruits are mature 40–50 days later.
Supposedly wild (or naturalized) Daucus carota plants occur in Eritrea and Ethiopia at 1800–2100 m altitude.
In their adaptation to the northern latitudes of Europe, carrots became biennial. Long days during the vegetative phase before vernalization do not cause bolting. They require vernalization at low temperatures to induce flowering. Carrots adapted to tropical and subtropical latitudes respond to long days by bolting even before the roots have properly thickened.
Carrots are mostly cultivated as a cool season crop. High soil temperatures, in excess of 25°C, induce slow growth rates, fibrous roots and low carotene content. For economic yields, carrots should be grown in tropical regions at altitudes above 1200 m or during the cool winter months in the subtropics. Early-maturing carrot cultivars may grow in the lowlands, but yields will be low and roots will have a poor colour. Optimum air temperatures are 16–24°C. Soils should be well drained, fertile and of a sandy texture. Heavy clay soils may induce malformed and twisted roots and harvesting will be difficult. Optimum pH is 6.0–6.5. A regular supply of water is essential to obtain smooth and even roots. Flowering and seed set are successful only in fairly dry climates with mean daily temperatures below 20°C.
Crop rotation is essential to reduce soilborne diseases and pests. Mulching after sowing is recommended to encourage germination. Seedlings may be earthed-up when roots start swelling to keep them cool and prevent green tops. In hot weather, light overhead shade is beneficial. Irrigation during dry spells is necessary to prevent irregular root development.
The nutrient removal of a crop of 20 t of fresh carrots is N 85 kg, P 20 kg, K 110 kg, Ca 60 kg and Mg 15 kg. Optimum fertilizer application will depend on soil nutrient reserves and expected yield level, but it is clear that carrots require relatively high doses of K fertilizer. Application of N 75–150 kg/ha, P 50–100 kg/ha and K 50–200 kg/ha is usually adequate. High N applications tend to cause excessive growth of foliage. Carrots are sensitive to high Cl concentrations and more susceptible to diseases at low soil pH. Liming or the use of Ca -containing fertilizers is recommended when pH is below 5.5. Well-decomposed organic manures are beneficial when applied with moderation (10–20 t/ha). Fresh organic matter, e.g. from a leguminous crop, can be detrimental to the carrot crop.
Propagation and planting
Seed multiplication at high latitudes with cold winters is based on stored and vernalized mature or young roots (stecklings) replanted in the field in spring (the root-seed method). In areas with mild winters and early snow cover, seeds are sown in late summer and the plants are left to overwinter in the field. These will bolt in spring and the seed-seed cycle is completed in 12–13 months. Carrot cultivars adapted to tropical regions have low vernalization requirements and can be propagated in highlands above 1200 m or during the cool period in arid and semi-arid regions. Carrot growers in such regions may maintain their cultivars by selecting the best mature roots and replanting them in a part of the field. Bolting and seed set soon follow.
The 1000-seed weight is 0.6–2.2 g. Seeds are sown, often mixed with sand, 1 cm deep in closely-spaced drills on finely prepared beds of soil cultivated to a depth of at least 30 cm. Plant densities range from 100 per m2 for large-rooted processing carrots, 175 per m2 for most fresh-market types to 250 per m2 for small-rooted baby carrots (4–8 kg seed per ha). Lower densities of 10–50 plants per m2 are applied in seed production fields. For hybrid seed production 8 rows of a female parent inbred line are alternated with 2 rows of a male one. Seed yields are increased significantly by placing beehives near the field during flowering. In-vitro propagation of carrots is easy and although researchers have experimented with ‘artificial seed’ in gel coating, this is too costly for practical application.
Diseases and pests
The major diseases in tropical carrot production are leaf blights (Alternaria dauci and Cercospora carotae) and root-knot nematodes (Meloidogyne hapla and other Meloidogyne spp.). ‘Kuroda’ has strong foliage with a remarkable field tolerance to Alternaria leaf blight, which may completely destroy the foliage of cultivars introduced from Europe. Crop loss by root-knot nematodes may be kept under control by crop rotation, e.g. with cereals and by the application of organic manure. Nematode infested soils can be treated by solarization, or with soil fumigants, although this is expensive and hazardous.
Other diseases are powdery mildew (Erysiphe polygoni and Erysiphe heraclei), bacterial blight (Xanthomonas campestris pv. carotae), black spot on roots (Alternaria radicina), and purple root rot (Helicobasidium brebisonii). Various root rots occur before or during storage, often after mechanical damage or as secondary pathogens (Botrytis cinerea, Fusarium spp., Sclerotinia sclerotiorum, Pythium violae and related spp., Erwinia carotovora). Root diseases are more severe in heavy soils with a poor structure. A total of 14 virus diseases have been identified in carrots, the most important being carrot red leaf virus (CaRLV). Carrot can be affected by aster yellows, a phytoplasma.
The most noxious pest of carrot in temperate areas is carrot root fly (Psila rosae) to which some degree of resistance has been found in ‘Sitan’ and in the wild species Daucus capillifolius Gilli from Libya. The lygus bug (Lygus hesperus and Lygus elisus) on seed crops, aphids (e.g. Cavariella aegopodii) as vectors of virus diseases, the leafhopper Macrosteles fascifrons as vector of aster yellows, carrot weevil (Listronotus oregonensis) and other foliage pests have all been reported in carrot, but probably the only pest which may cause serious crop losses in Africa is army worm (Spodoptera spp.).
Carrot is mostly harvested manually by pulling up the roots at the leaves. This requires strong and healthy foliage. Mechanical harvesting (in Europe, United States) is also based on pulling up by the foliage, or first topping the leaves and then lifting the carrots as in potato harvesting. In Africa carrots are usually ready for harvesting 60–85 days after sowing. Mature roots should be orange-coloured internally down to the blunt tip. In seed production fields the primary umbels are sometimes harvested prior to the main seed crop, as these ripen earlier and produce the largest seeds.
World average yield in 2002 was 21 t/ha of fresh carrot roots. In tropical Africa yields vary from 8–12 t/ha; higher yields are obtained in East Africa above 1500 m altitude. In Europe and the United States 30–120 t/ha can be harvested, depending on the type of cultivar and management. Marketable yield is also much influenced by plant density and time of harvest. Root weight and uniformity are closely related to seed size and quality.
Seed yields are 800–2000 kg/ha for open-pollinated and 700–1200 kg/ha for F1-hybrid cultivars.
Handling after harvest
Carrots bunched with leaves will store up to 3 weeks in a cool place, but can remain in good condition for 100–150 days when topped (foliage removed) and stored at 1–4°C with 95–100% relative humidity. Carrots should be stored separately from other vegetables to prevent development of a bitter flavour induced by ethylene. Generally carrots store better when the dry matter content is high, when they are grown on soils with low organic matter content, when they are mature and harvested under moist conditions, undamaged and free of diseases and pests. Carrots may be graded according to weight classes: A (< 50 g), B (50–200 g), C (200–400 g) and D (> 400 g). Carrots for the export market are carefully washed after removal of damaged roots, graded into different sizes according to the market requirement and packaged in perforated polythene bags. Small-scale farmers in Africa simply pack topped carrot roots in sacks for transportation to the local markets. This may cause considerable post-harvest losses.
The genetic basis of modern orange carrot cultivars is rather narrow, considering that they are mostly derived from a few 18th-century Dutch cultivars. Exploitation of the genetic variation existing in wild Daucus germplasm in the Mediterranean and south-western Asian regions started only recently. Germplasm collections of Daucus carota and related species, totalling some 5600 accessions, are available in Europe (United Kingdom, France, Netherlands), Russia, United States and Japan.
Before 1960 breeding methods were based on mass selection in open-pollinated populations, but F1-hybrids with greater uniformity are now increasingly replacing the older cultivars, particularly in Europe, the United States and Japan. Seed production of F1-hybrid cultivars is based on cytoplasmic male sterility of one of the parent inbred lines. Two types are used: the brown anther type, in which the anthers degenerate before anthesis, based on S-cytoplasm and at least two recessive genes with complementary action, and the petaloid type, in which the anthers are replaced by 5 additional petals, based on S-cytoplasm and at least two dominant genes with complementary action. The development and maintenance of inbred lines is complicated by severe loss of plant vigour after a few generations of inbreeding.
Main breeding objectives are improvements in total yield of fresh roots but also seed (F1-hybrids in particular), growth rate and earliness, uniformity of root size and shape, lightly shouldered tops without greening, small core and no internal greening, dark orange external and internal colour, smooth skin and absence of large laterals, resistance to cracking and breaking of the root during harvesting and post-harvest handling, taste, flavour, texture, carotene content, strong foliage, non-bolting, resistance to diseases and pests and heat tolerance for warm climates. The most popular cultivars are somewhat conical, as these break less easily during harvesting.
Carrot will be of increasing importance in tropical Africa. It is a valuable vegetable to be promoted in areas with vitamin A deficiency in human nutrition (where no red palm oil is used as kitchen oil). Adaptation to lowland tropical climates will remain limited. Genetic transformation is relatively easily achieved in carrot and offers interesting opportunities for developing cultivars resistant to important diseases and pests, which are difficult to realize by conventional breeding. Transgenic carrot plants also appear to be capable of producing recombinant proteins used for medicinal purposes in large quantities and at low costs.
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Sources of illustration
• van der Vossen, H.A.M. & Sambas, E.N., 1993. Daucus carota L. In: Siemonsma, J.S. & Kasem Piluek (Editors). Plant Resources of South-East Asia No 8. Vegetables. Pudoc Scientific Publishers, Wageningen, Netherlands. pp. 167–171.
Correct citation of this article:
van der Vossen, H.A.M. & Kahangi, E., 2004. Daucus carota L. In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, habit of cultivated plant; 2, part of leaf; 3, inflorescence; 4, infructescence; 5, fruit.
Redrawn and adapted by Achmad Satiri Nurhaman
‘Chantenay’ type, market in Mauritius
commercial production, Kenya
flowering plant habit