Daucus carota (carrot)

Progressing from its initial use as a medicinal plant, carrot has become a major world vegetable and is one of the most widely grown and important vegetables in the family Apiaceae. The modern carrot probably evolved from the wild carrot Daucus carota subsp. carota. Carrot is a cool-season, biennial dicot, whose fleshy axis is the edible tissue consumed as food. Carrot plants form a rosette of leaves and a large fleshy storage taproot during the first year. The stem is very compressed like a plate during the first year of growth, with foliage height generally ranging between 25-60 cm. The leaves or tops are inedible. The primary reason for selling carrots with tops is to show freshness of product, since the leaves are discarded and not consumed. Bunched carrots are more expensive because extra effort is required to keep the tops looking fresh without wilting. Bunched carrots have been largely replaced by roots sold in plastic bags. As a carrot flowers, anthers mature and fall before pistils become receptive. This characteristic is called protandry, and is a strategy to increase cross-pollination by insects, primarily bees. Pollen must come from different plants or from later maturing umbels on the same plant for successful pollination. Therefore, carrot seeds are a mixture of self- and cross-pollination, which increases variability. There is more diversity of carrot root shapes and sizes then usually seen in commercial markets. Preferences for carrot root shape and colour vary regionally. Carrot cultivars are sometimes grouped into two broad classes: eastern or Asian and western or European. European cultivars are firm, sweet, highly flavoured, yellow-orange to strongly orange in colour, slow bolting, and adapted to cool temperatures. Asian cultivars tend to have a softer texture, are less sweet, less flavoured, adapted to warm temperatures, bolt easily, and may be red or red-orange coloured.

Principal sources: Welbaum (2015)

Wild carrot, the progenitor of the cultivated carrot, is a biennial weed native to Europe, southwestern Asia and North Africa. Being a prolific seed producer, it can spread rapidly, and in its introduced range in North America and Australia it invades open grasslands, meadows, roadsides, abandoned fields, waste areas and degraded prairies, competing with and displacing native plants. Wild carrot can also negatively affect commercial carrot cultivation through genetic introgression in seed crops.

Daucus carota is a complex, very variable species comprising wild and cultivated carrots, resulting in a confused taxonomy. The complex is subdivided into 13 subspecies, 12 for wild taxa and one for the cultivated taxon (subsp. sativus (Hoffm.) Arc.). However, for cultivated carrot it is better to classify directly at cultivar level below the species level.

There are two main groups of cultivated carrot: the eastern (anthocyanin) and western (carotene) carrot. The eastern carrot has branched roots, is yellow, reddish-purple to purple-black, rarely yellowish-orange; leaves slightly dissected, greyish-green, pubescent; flowering in the first year. The western carrot has unbranched roots and is 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 western Europe and the USA from the Dutch landraces 'Long Orange' and 'Horn'.

Cultivated carrots cross readily with the wild carrot taxon D. carota subsp. carota, which is very common in Europe and South-West Asia and has been introduced and naturalized elsewhere, notably to North America and Australia. In America it is known as 'Queen Anne’s Lace'. The modern carrot probably evolved from a wild plant resembling Queen Anne’s Lace. There are several other wild carrot taxa and Daucus species occurring in the Mediterranean area and South-West Asia, most of which are crossable with the cultivated carrot.

Annual or biennial erect herb, 20-50 cm tall at the mature vegetative stage and 120-150 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; the core (xylem) of mature roots is usually somewhat lighter in colour than the phloem, and the top of the root is often green. Leaves 8-12, growing in a rosette, glabrous, green, with long petiole often sheathed at its base; leaf-blade 2-3-pinnate, the segments divided into often linear ultimate lobes. Flowering stalks few to several, branched, each branch ending in a compound umbel (inflorescence); each umbel comprising 50 or more umbellets, each of which has up to ca. 50 flowers; involucral bracts more or less pinnatipartite; primary rays 2-25 cm, secondary rays 1-6 cm, pedicels 0.5-1.5 cm long; flowers mainly bisexual in primary umbels, in umbels of higher order an increasing number of male flowers may occur in addition to bisexual flowers; a few purple-red sterile flowers may be present in the central umbellets, especially in wild plants; flower small, 2 mm in diameter, epigynous, white, 5-merous but with 2 carpels and 2 styles. Fruit an oblong-ovoid schizocarp, 2-4 mm long, at maturity splitting into 2 mericarps, primary ridges ciliate, secondary ridges with hooked spines. Seed (inside the mericarp) with a long embryo embedded in endosperm. Seedling with long, thin taproot, cordate cotyledons and pinnate first true leaves.

It is generally assumed that the purple (anthocyanin-containing) carrot originated in Afghanistan in the region where the Himalayan and Hindu Kush mountains are confluent, and that it was domesticated also in Afghanistan and adjacent regions of Russia, Iran, India, Pakistan and Anatolia. Purple carrot, together with a yellow variant, spread to the Mediterranean area and Western Europe in the 11-14th centuries, and to China, India and Japan in the 14-17th centuries. The orange (carotene-containing) 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 were the basis for the orange carrot cultivars grown at present all over the world. In Asia they have now largely replaced the purple and yellow types because of superior yield and changing fashion.

The wild carrot, D. carota subsp. carota, is very common in Europe and South-West Asia and has been introduced to North America, Australasia and elsewhere.

Wild carrot, also known as bird’s nest, bishop’s lace and (in North America) Queen Anne’s lace, is native to temperate regions of Europe, southwestern Asia and North Africa, and is naturalized in North America, Japan, New Zealand and Australia (NatureWatch NZ, 2015). It was probably introduced to North America from Europe as a weed seed contaminant in imported grain by the earliest colonists in the early 17th century. Cultivated carrots could also have escaped from gardens to become naturalized. Wild carrot now occurs at different levels of weediness in most eastern and southern Canadian provinces and all 48 contiguous states of the USA (USDA-NRCS, 2015), with reports also from Alaska and Hawaii (NatureWatch NZ, 2015). In Australia wild carrot is thought to have originated in the carrot seed that was imported from the UK to the colony of Sydney between 1786 and 1798 for food production; it is now present in every state and is commonly found naturalized in coastal regions around heavily populated areas, particularly in the south east of the country and Tasmania (Weeds in Australia, 2015).

Wild carrot already occurs in many temperate regions of the world. Although cultivated carrot is harvested before it produces seeds, escapes from cultivation do occur, allowing the establishment of wild populations.

In Australia, wild carrot invades open ground and competes with native grasses and herbs for resources. The plant poses a threat to recovering grasslands, as it matures faster and grows larger than many native plants (Weeds in Australia, 2015). In the USA, where it is listed as a noxious weed in the states of Iowa, Michigan, Ohio and Washington (USDA-NRCS, 2015), it is one of many alien species to invade the prairies in the west of the country, displacing native plant species, such as Sidalcea nelsoniana (US Fish and Wildlife Service, 1998). Throughout its range, where it occurs in the vicinity of cultivated carrots, especially those being grown for seed production, it can cross pollinate, resulting in a genetically contaminated seed crop (Grzebelus et al., 2011).

Similar in appearance to Conium maculatum, the deadly poison hemlock, D. carota is distinguished by a mix of tri-pinnate leaves, fine hairs on its leaves and slender, solid, green stems, a root that smells like carrots, occasionally a single dark red flower in the centre of the umbel, shorter stature and summer rather than late spring flowering. Poison hemlock has purple-spotted, smooth, hollow and relatively stout stems and hairless leaves. Another wild carrot-like highly toxic plant is spotted waterhemlock (Cicuta maculata), and this has a cluster of enlarged roots that smell like parsnip, rather than a single taproot that smells of carrot. Wild parsnip (Pastinaca sativa) is not poisonous and can be distinguished from wild carrot by coarsely toothed rather than feathery leaves, and yellowish rather than white flowers (Penn State Extension, 2015).

The domesticated carrot (D. carota subsp. sativus) is easily differentiated from wild carrot (D. carota subsp. carota) by its highly pigmented, fleshy, edible, brittle, non-fibrous roots. In wild carrots, fresh roots are generally yellowish, flexible and fibrous, becoming tough and woody due to high xylem content. Also, the transition from shoot to storage organ is indistinct externally (abrupt in cultivated carrot), rosette foliage is often prostrate (usually conspicuously erect in domesticated forms), and umbels often have one or several purple central flowers (rarely in domesticated forms) (Encyclopedia of Life, 2015).

Wild carrot can be found growing in rough grassland, along coastal cliffs and in dunes, as well as in overgrown thickets, weedy meadows, along railroads and roadsides, abandoned fields, degraded prairies and waste lands. In some situations, wild carrot can spread aggressively, its deep taproot making it difficult to extirpate by mowing or hand-pulling (Hilty, 2015).

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. Germination is epigeal with first appearance of seedlings 9-12 days after sowing. The first four true leaves are formed at 4 to 5-day intervals, starting 3-4 weeks after sowing, but then the interval increases gradually to 15-18 days for subsequent leaves. 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 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 70-120 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 eight 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 approximately 16°C. The generative phase is accelerated by long days after devernalization (20°C). First a new rosette of leaves is formed, followed by elongation of the flowering stalk and first flowering 3 months later. Flowers are arranged in spirals and development is centripetal: the first mature flowers are on the outer edges of the outer umbellets. Flowering may last for one month, starting with the primary umbel. Initially the umbels are flat and concave. At anthesis the umbellets turn downwards progressively from the outside towards the centre, so that by the time the central flowers are mature, the umbels are more or less convex to conical. After pollination the umbellets turn upwards again. 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 seeds (mericarps) are mature 40-50 days later.

Ecology

In their adaptation to the northern latitudes of Europe, carrots became biennial and tolerant of long days (non-bolting) during the vegetative phase. They require subsequent 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 700 m. 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 climates with mean day temperatures below 20°C.

Carrots are susceptible to root splitting/cracking/breakage. Widely spaced carrots and large roots are more likely to exhibit early splitting and produce more secondary roots. Variations in growth rate and soil moisture availability are suspected causes. Shatter cracking is initiated by mechanical damage. High root turgidity appears to increase susceptibility.

Splitting, cracking and root breakage during harvest and subsequent handling are more common when soils are cold and susceptibility is highest in early morning. Early morning harvesting and careful handling during harvesting can decrease the damage.

Root forking is often due to early damage or obstruction of the taproot apical meristem, by stones or hard pans in the soil, which leads to distortion and multiple-rooting. Nematodes, fungi and insect-feeding can also cause deformed and forked roots.

Air pollution, e.g. high ozone, can cause bleached stippling to the upper leaf surfaces of carrot plants. Sulfur dioxide and ethylene can also cause plant injuries.

Principal sources: Rubatzky et al. (1999)

The best known natural enemy of wild carrot in eastern North America is the black swallowtail (Papilio polyxenes), the caterpillars of which feed on the leaves of a range of plants in the family Apiaceae. In temperate regions, pests attacking cultivated carrot crops often attack wild carrot. The most noxious pest of carrot in temperate areas is carrot root fly (Psila rosae), whose larvae burrow into the roots. Other insects feeding destructively on the plant’s parts include root-feeding larvae of Listronotus oregonensis and Ligyrus gibbosus, and foliage-eating larvae of the moth Melanchra picta (Wagner, 2005; Hilty, 2015). Wild carrot is a summer host for such aphids as Cavariella aegopodii, Dysaphis apiifolia, Hyadaphis foeniculi and H. passerinii (Blackman and Eastop, 2013). Another principal European pest is the root-damaging carrot cyst nematode (Heterodera carotae).

In North America, seeds are eaten by the ring-necked pheasant, ruffed grouse and pine mouse. The aromatic and somewhat bitter foliage is browsed sparingly by mammalian herbivores, such as deer and rabbits (Hilty, 2015).

The ability of wild carrots to act as reservoirs of disease for cultivated carrot crops is sparsely documented, even though fungi responsible for diseases in cultivated carrot are likely pathogenic on wild carrot. For example, wild carrots were identified as sources of Alternaria dauci infection in New Zealand carrot crops (Soteros, 1979), while Sherf and MacNab (1986) identified wild carrot as a reservoir of Carrot mottle virus.

Wild carrots appear to be an important source of Carrot mottle virus infection in cultivated carrot crops (Sherf and MacNab, 1986). They may harbour other pests and diseases that will attack commercial crops. Hybridization with the commercial plant can result in poor seed production.

In its introduced range, wild carrot as an invasive weed can displace native plants. In Oregon in the USA, Nelson's checker-mallow (Sidalcea nelsoniana) was federally listed as threatened without critical habitat in 1993. A recovery plan was published in 1998 (US Fish and Wildlife Service, 1998) and updated in the 2010 Recovery Plan for the Prairie Species of Western Oregon and Southwest Washington (US Fish and Wildlife Service, 2010). It is a perennial herb in the family Malvaceae with tall, lavender to deep pink flowers, and occurs mainly in open areas with little or no shade (US Fish and Wildlife Service, 2015). It is threatened throughout its range by encroaching successional species, primarily resulting from suppression or elimination of natural disturbance regimes including periodic flooding and fires. Populations in Oregon’s Willamette Valley are extremely imperilled, as agricultural and urban development have modified and depleted habitats, fragmenting populations into mostly small, widely scattered patches. Extirpation is an ongoing threat to many Nelson’s checker-mallow occurrences on private lands, roadsides, undeveloped lots and otherwise vulnerable sites. In addition to land use threats, populations are particularly subject to competitive exclusion by exotic species (US Fish and Wildlife Service, 1998). Some 111 plant species are associated with Nelson’s checker-mallow, with about half of them being non-native. Most sites in the Willamette Valley have been densely colonized by invasive weeds, including wild carrot, but Nelson’s checker-mallow appears to be the listed prairie species most readily recoverable. Several recovery actions for habitat restoration have been implemented, including obtaining seeds and establishing plants, and evaluating the efficacy of habitat management techniques and ways to reduce the competition threat from non-native plants. Nelson’s checker-mallow plants have responded well to various management activities such as out-planting, transplanting, mowing and burning (US Fish and Wildlife Service, 2012).

Carrots are one of the most popular vegetables worldwide. The swollen taproot of carrot is eaten and is an important market vegetable, even in tropical areas. The roots are consumed raw or cooked, alone or in combination with other vegetables (for example, peas), as an ingredient of soups, sauces, salads and in dietary compositions. Carrots are often canned, dehydrated, or quick frozen. Large quantities are also processed into infant food, juice or as an ingredient of soups, sauces and stews. A part of production is used as fodder. Young leaves are sometimes eaten raw or are also used as fodder (Elzebroek and Wind, 2008).

Propagation and PlantingSeed 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 are propagated in highland regions above 1200 m. Highland carrot growers often maintain their cultivars by selecting the best mature roots and replanting them at one end of the field. Bolting and seed set soon follow. Seeds are sown, often mixed with sand, 1-2 cm deep in drills 10-15 cm apart in finely prepared soils previously cultivated to a depth of at least 30 cm. Seedlings are thinned to 5-8 cm in the rows. Seed requirements (200 plants/m²and 70% germination) for the dominant half-long carrot cultivars used in Asia, are 4-5 kg/ha. For bigger carrots, the density may be reduced to about 100 plants/m².HusbandryCrop rotation is essential to reduce soilborne diseases and pests. Mulching (rice straw) after sowing is recommended to encourage germination. Radish seedlings may be grown to protect carrot seedlings in the winter. Seedlings may be earthed-up when roots start swelling to keep them cool and prevent green tops. 15 to 20°C is optimal for seed development. In hot weather, light overhead shade is beneficial. Irrigation during dry spells is necessary to prevent irregular root development. Nutrient requirements of carrots are particularly high for K (200-300 kg/ha), low to medium for N (100-150 kg/ha), normal for P, Ca, Mg and other elements. Carrots are sensitive to high Cl concentrations and more susceptible to diseases at very high 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 moderately (10-20 t/ha). Fresh organic matter, for example, from a leguminous crop, can be detrimental to the carrot crop.HarvestingCarrot is mostly harvested manually by pulling up the roots at the leaves. This requires strong and healthy foliage. Mechanical harvesting (in Europe, USA) is also based on pulling up by the foliage, or first topping the leaves and then lifting the carrots as in potato harvesting. In Asia carrots are usually ready for harvesting 70-85 days after sowing. Mature roots should be orange-coloured internally down to the blunt tip.In Europe and the USA, yields of 30-120 t/ha can be reached, depending on the type of cultivar and culture. In Asia yields vary from 8-20 t/ha; higher yields are possible above 800 m altitude. Marketable yield is much influenced by plant density and time of harvest. Root weight and uniformity are closely related to seed size and quality. Seed yields are 200-500 kg/ha.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 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, and undamaged and free of diseases and pests. Carrots may be graded according to weight A <50 g), B (50-200 g), C (200-400 g) and D (>400 g).

Carrots take approximately 3 months to mature in the tropics; the earlier, short-rooted cultivars take less time to reach maturity than the longer rooted cultivars. Subsistence farmers should use the crop from the ground as required, unless there is a niche market locally to justify a bulk harvest. The root crop does not store well except at lower temperatures and this is not normally economic in the tropics.

Many cultivars exist, which makes it possible to sow carrots in all seasons except the winter. When carrots can be harvested depends on cultivar, desired size and growing conditions. Full-grown carrots require up to 125 days to mature, baby carrots require 60-80 days. However, it is possible to harvest carrots any time when they have a usable size, maturing is not necessary. In Asia carrots are usually ready for harvesting 70-85 days after sowing. 

Mechanical harvesting is routinely used for large scale commercial production. There are two main types of machine, top lifters and share lifters; each of which may be tractor drawn or self-propelled. In a top lifter the roots are undercut while belts simultaneously grasp the foliage, lifting the entire plant from the soil. Top lifters are used where the tops remain strong up till harvest, with the crop commonly sold fresh rather than going into store. Share lifters are used where the tops senesce, due to maturity, disease or cold. Where foliage remains dense prior to use of a share lifter it is topped first and the foliage removed, a share is then used to get the carrots out of the ground from underneath. Hand harvesting remains common in subsistence and very small scale commercial production.

A part of the carrot production for the fresh market is bunched with leaves, washed to clean the roots and hydrocooled or iced to reduce temperature and respiration. Most carrots are topped, which means that the leaves and sometimesthe top of the ‘root’ are removed.

There is more diversity of carrot root shapes and sizes than usually seen in commercial markets, and preferences vary regionally. Carrot cultivars are sometimes grouped into two broad classes: eastern or Asian and western or European., Eastern (anthocyanin) carrots have an annual habit. The root is branched, yellow, reddish-purple to purple-black, rarely yellowish-orange. Leaves are slightly dissected and are pubescent giving them a gray-green colour; they are adapted to warm temperatures and bolt easily; some tropical Asian cultivars can be induced to bolt at temperatures less than 15°C. The greatest diversity of these carrots is found in Afghanistan, Russia, Iran and India. Western (carotene) carrots have strong biennial characteristics but are often annual in tropical regions. The root is unbranched, yellow, orange or red, occasionally white. The leaves are strongly dissected, bright green and sparsely hairy.  They are more tolerant of low temperatures that induce bolting. European cultivars are firm textured, sweet, highly flavoured, yellow-orange to strongly orange in colour. Most likely these carrots derived from the first group by selection among hybrid progenies of yellow Eastern carrots, white carrots and wild subspecies grown in the Mediterranean (http://www.carrotmuseum.co.uk/atoz.html).

At present, the western carrot is by far the most important, although the eastern carrot is still cultivated in some Asian countries. Therefore, the majority of world breeding efforts focus on this type because of their large market share and crop value. Cultivars are often grouped into types that reflect similar morphology or horticultural characteristics. Western cultivars are often classified into three categories based on root shape and length. Short-rooted cultivars, which mature quickly (50–60 days) for early season fresh-market production, include ‘Oxheart’, ‘Early Mokum’, ‘Parisian Market’, ‘Early Nantes’, and ‘Amsterdam Forcing’. Medium-rooted cultivars are used for main-season production for both fresh market and processing. Cultivars mature in 60–75 days from seeding, and include ‘Mokum’, ‘Flakkee’, ‘Autumn King’, ‘Danvers’, and ‘Royal Chantenay’. Long-rooted cultivars such as ‘Imperator’ are usually grown in thoroughly tilled deep loam or muck soils and mature 60–75 days from seeding. The tropical Asian cultivars also vary by root shape ‘Kuroda’ resemble the ‘Danvers’ or ‘Chatenay’ types, while ‘Brasilia’ and ‘Southern Nantes’ resemble ‘Nantes’.

Some of the major commercial carrot types or classes of carrot roots are described as follows:

All cultivars can be used for fresh market, but some are better suited for processing. For processing, larger-rooted cultivars like ‘Danvers’ or ‘Chantenay’ are preferred. Different cultures prefer specific root colours and shapes, so additional types are also grown. In Japan, where carrots are seldom eaten raw, long reddish orange carrots, like ‘Kuroda’, or even red or purple cultivars with a thick cylindrical shape are preferred. In contrast, there is a preference for relatively short, slender, yellow-orange ‘Nantes’ and ‘Nantes’-like cultivars in Europe, while in North America the long, deep orange ‘Imperator’ and related cultivars predominate.

Researchers have developed new cultivars of carrots with novel traits through traditional breeding methods. Cultivar development involves initial crosses between root type classes, especially with in the western and eastern types. Crosses between carrots form these two climatic regions are also made, but less frequently. There is enough genetic diversity among these classes to easily allow ‘Danvers’ types to be derived from ‘Chantenay’ x ‘Imperator’, or ‘Nantes’, and even allow ‘Imperator’ types to be derived from ‘Chantenay’ x ‘Danvers’. Hence the effective germplasm pool for carrot root shape modification by breeding is very large. Furthermore, crosses of domesticated x wild carrot can be used to derive satisfactory domesticated types, although larger populations, more time and considerable backcrossing to domesticated stocks is required. Transgenic carrots produced through genetic engineering have not had an impact on world markets as of 2013. Novel yellow, white and red cultivars are gaining popularity in some markets because they add variety and variation to salads and other foods containing carrots.

There has been a gradual conversion to F1 carrot cultivars since the 1970s in the USA and Europe because of their greater uniformity and productivity. There is little variation among individual plants in a high quality carrot cultivar. Cytoplasmic male sterility (CMS) is used to ensure that inbred lines are cross-pollinated to produce seeds of hybrid cultivars. Open-pollinated cultivars remain popular for certain applications where the extra cost of F1 seeds is not worth the investment, such as for processing into cut products.

 Principal sources: Welbaum (2015)

Carrots are propagated from seed. Because of the seed shape and the presence of spines, seeds are often pelleted. Seed is mostly drilled with a precision seeder to a depth of 1-2 cm. Seed rate depends primarily on the size of roots required.and can range from1.0 to 4.5 kg (unpelleted) per hectare. Good seedbed preparations are essential because carrot seed germinates slowly and irregularly, and the seedling is rather weak. Seeds are sown, often mixed with sand, 1-2 cm deep in drills 10-15 cm apart in finely prepared soils previously cultivated to a depth of at least 30 cm. A light mulch of chopped straw or similar material should be applied after sowing to prevent soil capping and also assist the reduction of subsequent soil temperatures. Seed requirements (200 plants/m² and 70% germination) for the dominant half-long carrot cultivars used in Asia, are 4-5 kg/ha. For bigger carrots, the density may be reduced to about 100 plants/m². At germination the soil therefore has to crumble easily. Seedlings are thinned to 5-8 cm in the rows. The spacing in the row depends on the desired root size at time of harvest; the rows may be 15-40 cm apart. Too dense spacing must be avoided because that often results in deformed roots. The minimum temperature for germination is 4°C. The first appearance of seedlings is 10-15 days after sowing. In the juvenile stage the plant develops a leaf rosette and starts thickening the taproot; the hypocotyl is drawn into the soil by root contraction. Using coated or pelleted seed assists in obtaining an even seedling stand and should minimize the need for post emergence thinning. Erecting a lightweight shade structure over the crop can improve quality in high temperature environments.

Seed production in the temperate regions requires two growing seasons. Carrots have to be vernalized at low temperatures to induce flowering. However, during the winter the plants must be covered to prevent frost damage. 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 are propagated in highland regions above 1200 m. Highland carrot growers often maintain their cultivars by selecting the best mature roots and replanting them at one end of the field. Bolting and seed set soon follow.

As wild carrots are widely distributed in the temperate regions, they can become a real threat where cultivated carrot seed is produced. The wild plants hybridize easily with the cultivated plants, resulting in a crop with valueless seed.

Principal sources: Elzebroek and Wind (2008)

Carrot is one of the richest vegetables in fibres and carotenoids. It also contains vitamin E (0.52 mg /g), vitamin C (0.07 mg/g) and polyphenols such as p-coumaric, chlorogenic and caffeic acids. Fresh carrots contain approximately 90% water, 1% protein, 7% carbohydrates (mainly sugar) and 1% fibre, furthermore Ca, Fe and vitamin C; the orange roots contain b-carotene, which is a prolific source of provitamin A. Carrots are especially rich in carotenoids. a-Carotene and b-carotene are the principal carotenoids in carrots, while lutein is a minor component. There is recent evidence that polyacetylenes in carrots and related members of the Apiaceae have anti-cancer properties, (Saleh et.al., 2013, Xu Xin et al., 2014).

Principal sources: Elzebroek and Wind (2008),  George (2009), Terry (2011)

Total world production of carrots and turnips was 37.2 million metric tonnes for 2013. China was by far the largest producer with a production level of 1.69 million tonnes accounting for 45.4% of the world total. The area harvested was 0.48 million ha and the average yield was 39.2 t/ha. After China, the top producers in 2013 were: Uzbekistan (1.6 million t), Russian Federation (1.6 million t) and USA (1.3 million t). All other countries combined produce account for around 42% of total carrots worldwide, reflecting the widespread production of this crop (FAOSTAT).

In China, the main producing provenances are Shandong and Henan in north central China. Export of carrots is predominately fresh although frozen exports are on the increase. Carrots are one of China's leading fresh vegetable exports. In 2005 the export value was $107 million compared to just $16 million in 2000. The main markets are Japan, ASEAN countries and South Korea (Dede, 2008).

Trends in carrot consumption reflect changes in product availability and improved information about the nutritional benefits from eating carrot. For example, after remaining constant for many years, US carrot consumption increased dramatically to a peak in 1990. This increase was likely caused by scientific information showing that carrots are an excellent source of dietary fibre and carotenoids, two factors known to be important for human nutrition. The available of convenience-packaged carrot items such as lightly processed baby-peeled carrots and shredded carrots in salad mixes also helped to increase consumption during the period. Since 1990, total carrot consumption has declined, with frozen carrot consumption declining sharply (Welbaum, 2015). In 2013, fresh per capita consumption was reported as 3.4 kg/person (FPP, 2015).

For current information on crop production, see FAO Statistics.

See also http://federalproducepolicy.com/news2015/mar_05_2015-carrot_summary.html

Principal sources: Welbaum (2015)

Carrot will continue to be an important vegetable worldwide, but adaptation to hot climates will remain limited. Resistance to important diseases and pests is becoming an increasingly important aspect of carrot breeding.

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