Key lime

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Key lime
Ripekeylime.jpg
Ripe yellow Key lime.
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Sapindales
Family: Rutaceae
Genus: Citrus
Species: C. × aurantiifolia
Binomial name
Citrus × aurantiifolia
(Christm.) Swingle

The Key lime (Citrus × aurantiifolia) is a citrus hybrid (C. micrantha x C. medica) with a spherical fruit, 2.5–5 cm (1–2 in) in diameter, that is yellow when ripe but usually picked green commercially.

It is smaller and seedier, with a higher acidity, a stronger aroma, and a thinner rind, than that of the Persian lime (Citrus × latifolia). It is valued for its unique flavor compared to other limes. The name is derived from its association with the Florida Keys, where it is best known as the flavoring ingredient in Key lime pie. It is also known as West Indian lime, bartender’s lime, Omani lime, or Mexican lime, the last classified as a distinct race with a thicker skin and darker green color. Philippine varieties have various names, including dayap and bilolo.[1]

Etymology[edit]

The English word "lime" was derived, via Spanish then French, from the Arabic word ليمة līma (Persian: لیموlimu).[2] "Key" is from Florida Keys, where the fruit is naturalized. The Oxford English Dictionary dates the first use of "key lime" to 1905, in an issue of Country Gentleman, which described the fruit as "the finest on the market. It is aromatic, juicy, and highly superior to the lemon."[3]

Description[edit]

C. aurantiifolia is a shrubby tree, to 5 m (16 ft), with many thorns. Dwarf varieties exist that can be grown indoors during winter months and in colder climates. Its trunk, which rarely grows straight, has many branches, and they often originate quite far down on the trunk. The leaves are ovate, 2.5–9 cm (1–3 12 in) long, resembling orange leaves (the scientific name aurantiifolia refers to this resemblance to the leaves of the orange, Citrus aurantium). The flowers are 2.5 cm (1 in) in diameter, are yellowish white with a light purple tinge on the margins. Flowers and fruit appear throughout the year, but are most abundant from May to September in the Northern Hemisphere.[4][5]

When in contact with the skin, the Key lime can sometimes cause phytophotodermatitis, in which a chemical reaction makes the skin extra sensitive to ultraviolet light.[6][7]

History[edit]

This particular cultivar is a citrus hybrid, Citrus micrantha × Citrus medica (a papeda-citron cross).[8][9][10]

C. aurantiifolia is native to Southeast Asia. Its apparent path of introduction was through the Middle East to North Africa, then to Sicily and Andalucia and via Spanish explorers to the West Indies, including the Florida Keys. From the Caribbean, lime cultivation spread to tropical and subtropical North America, including Mexico, Florida, and later California.

Since the North American Free Trade Agreement came into effect, many Key limes on the US market are grown in Mexico, Central America and South America. They are also grown in Texas, Florida, and California.

The Key lime has given rise to several other lime varieties. The best known, the triploid progeny of a Key lime-lemon cross, is the Persian lime (Citrus × latifolia), the most widely-produced lime, globally. Others are, like their parent, classed within C. aurantiifolia. Backcrossing with citron has produced a distinct group of triploid limes that are also of commercial value to a limited degree, the seedy Tanepeo, Coppenrath, Ambilobe and Mohtasseb lime varieties as well as the Madagascar lemon. Hybridization with a mandarin-pomelo cross similar to the oranges has produced the Kirk lime. The New Caledonia and Kaghzi limes appear to have resulted from an F2 Key lime self-pollination, while a spontaneous genomic duplication gave us the tetraploid Giant Key lime.[11][12] The potential to produce a wider variety of lime hybrids from the Key lime due to its tendency to form diploid gametes may reduce the disease risk presented by the limited diversity of the current commercial limes.[13]

Agronomy[edit]

Cultivation and propagation[edit]

Flowers of the Key lime plant

There are various approaches to the cultivation of Key limes. This variety of citrus can be propagated from seed and will grow true to the parent. The seeds must be kept moist until they can be planted, as they will not germinate if allowed to dry out.[citation needed] If the plants are propagated from seed, the seeds should be stored at least 5–6 months before planting.[14] Alternatively, vegetative propagation from cuttings or by air layering may permit fruit production within one year, and from genetically more predictable lines of plants. Or digging around a mature tree to sever roots will encourage new sprouts that can be transplanted to another location.[citation needed] Clones are often bud grafted[15] into rough lemon or sour orange to obtain strong root stocks (see also fruit tree propagation).

It is often advisable to graft the plants onto rootstocks with low susceptibility to gummosis, because seedlings generally are highly vulnerable to the disease. Useful rootstocks include wild grapefruit, cleopatra mandarin and tahiti limes.[14] C. macrophylla is also sometimes used as a rootstock in Florida to add vigor.

Climatic conditions and fruit maturation are crucial in cultivation of the lime tree. Under consistently warm conditions potted trees can be planted at any season, whereas in cooler temperate regions it is best to wait for the late winter or early spring. The Key lime tree does best in sunny sites, well-drained soils,[16][17] good air circulation, and protection from cold wind. Because its root system is shallow, the Key lime is planted in trenches or into prepared and broken rocky soil to give the roots a better anchorage and improve the trees' wind resistance. Pruning and topping should be planned to maximise the circulation of air and provide plenty of sunlight. This keeps the crown healthily dry, improves accessibility for harvesting, and discourages the organisms that cause gummosis.[14]

Harvesting[edit]

White key lime flower in different stages.

The method of cultivation greatly affects the size and quality of the harvest. Trees cultivated from seedlings take 4–8 years before producing a harvest. They attain their maximal yield at about 10 years of age. Trees produced from cuttings and air layering bear fruit much sooner, sometimes producing fruit (though not a serious harvest) a year after planting. It takes approximately 9 months from the blossom to the fruit. When the fruit have grown to harvesting size and begin to turn yellow they are picked and not clipped. To achieve produce of the highest market value, it is important not to pick the fruit too early in the morning; the turgor is high then, and handling turgid fruit releases the peel oils and may cause spoilage.[14]

Postharvest process[edit]

3 key lime fruits with persistent styles.

Shelf life of Key limes is an important consideration in marketing. The lime still ripens for a considerable time after harvesting, and it is usually stored between 12.5 and 15.5 °C (55–60 °F) at a relative humidity of 75–85%. Special procedures are employed to control the shelf life – for example, applications of growth regulators, fruit wax, fungicides, precise cooling, calcium compounds, silver nitrate, and special packing material. The preferred storage conditions are temperatures of 9–10 °C (48–50 °F) and a humidity over 85%, but even in ideal conditions post-harvesting losses are high.

In India most Key lime producers are small scale farmers without access to such post-harvesting facilities, but makeshift expedients can be of value. One successful procedure is a coating of coconut oil that improves shelf life, thereby achieving a constant market supply of Key limes.[18]

Key limes are made into black lime by boiling them in brine and drying them. Black lime is a condiment commonly used in the Middle East.

Yield[edit]

The yield varies depending on the age of the trees. Five- to seven-year-old orchards may yield about 6 t/ha (2.7 tons/acre), with harvests increasing progressively until they stabilise at about 12–18 t/ha (5.4–8 tons/acre). Seedling trees take longer to attain their maximal harvest, but eventually out-yield grafted trees.[14]

References[edit]

  1. ^ "Dayap / Citrus aurantifolia / LIME: Philippine Medicinal Herbs / Philippine Alternative Medicine". Stuartxchange.org. Retrieved 2013-12-20. 
  2. ^ "Lime". Merriam-Webster Dictionary. Retrieved 2017-09-23. 
  3. ^ "key, n.2". OED Online. September 2013. Oxford University Press. Accessed 24 October 2013.
  4. ^ P. Golob; Food and Agriculture Organization of the United Nations (1999). "Alphabetical List of Plant Families with Insecticidal and Fungicidal Properties". The use of spices and medicinals as bioactive protectants for grains. Food & Agriculture Org. pp. 13–. ISBN 978-92-5-104294-6. Retrieved 19 June 2011.  Webarchive mirror
  5. ^ Citrus aurantiifolia Swingle. Hort.purdue.edu. Retrieved on 2011-06-19.
  6. ^ Weber, I. C.; Davis, C. P.; Greeson, D. M. (1999-03-01). "Phytophotodermatitis: the other "lime" disease". The Journal of Emergency Medicine. 17 (2): 235–237. doi:10.1016/s0736-4679(98)00159-0. ISSN 0736-4679. PMID 10195477. 
  7. ^ "Phytophotodermatitis on Fingers of a Young Child | Patient Care Online". www.patientcareonline.com. 2003-04-01. Retrieved 2017-03-04. 
  8. ^ Curk, Franck; Ancillo, Gema Ancillo; Garcia-Lor, Andres; Luro, François; Perrier, Xavier; Jacquemoud-Collet, Jean-Pierre; Navarro, Luis; Ollitrault, Patrick (2014). "Next generation haplotyping to decipher nuclear genomic interspecific admixture in Citrus species: analysis of chromosome 2". BMC Genetics. 15: 152. 
  9. ^ "Citrus × aurantiifolia". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 11 December 2017. 
  10. ^ Nicolosi, E.; Deng, Z.N.; Gentile, A.; La Malfa, S.; Continella, G.; Tribulato, E. (2000). "Citrus phylogeny and genetic origin of important species as investigated by molecular markers". Theoretical and Applied Genetics. 100 (8): 1155–1166. doi:10.1007/s001220051419. 
  11. ^ Curk, Franck; Ollitrault, Frédérique; Garcia-Lor, Andres; Luro, François; Navarro, Luis; Ollitrault, Patrick (2016). "Phylogenetic origin of limes and lemons revealed by cytoplasmic and nuclear markers". Annals of Botany. 11: 565–583. doi:10.1093/aob/mcw005. PMC 4817432Freely accessible. 
  12. ^ Ali, Muhammad Amjad; Nawaz, Muhammad Azher (2017), "Advances in Lime Breeding and Genetics", in Khan, M. Mumtaz; Al-Yahyai, Rashid; Al-Said, Fahad, The lime: botany, production and uses, CAB International, pp. 37–53 
  13. ^ Rouiss, H; Bakry, F; Froelicher, Y; Navarro, L; Aleza, P; Ollitrault, P (2018). "Origin of C. latifolia and C. aurantiifolia triploid limes: the preferential disomic inheritance of doubled-diploid 'Mexican' lime is consistent with an interploid hybridization hypothesis". Annals of Botany. 121: 571–585. doi:10.1093/aob/mcx179. 
  14. ^ a b c d e Duke J.A., duCellier J.L. (1993): CRC handbook of alternative cash crops (page 139-145)
  15. ^ "T or Shield Budding". tamu.edu. 
  16. ^ Morton, Julia F. (1987). "Mexican Lime". Fruits of warm climates. Purdue. pp. 168–172. 
  17. ^ "Home Fruit Production". tamu.edu. 
  18. ^ Bisen A., Pandey S.K., Patel N.: Effect of skin coatings on prolonging shelf life of kagzi lime fruits (Citrus aurantiifolia Swingle). Journal of Food Science Technology (2012) 49(6).753-759. (page 139–145)

External links[edit]