1 Introduction and Overview of Lime M. Mumtaz Khan1*, Rashid Al-Yahyai1 and Fahad Al-Said2 1Department of Crop Sciences, College of Agricultural and Marine Sciences, Sultan Qaboos University, Muscat, Oman; 2Assistant Secretary General for Innovation Development, The Research Council, Muscat, Oman Lime, lemon and citron belong to the acid citrus edible part of the fruit is divided by carpel fruit group. This group is characterized by an el- segments or locules. There are many juice ve- liptical to round shaped fruit with high citric sicles within the carpels (Ting and Attaway, acid content. Limes can be distinguished from 1971; Rivera-Cabrera et al., 2010) (Fig. 1.1). other fruit in the citrus family as they have both The number of carpels vary, with acid lime acid and sweet varieties. The differences in tree fruit normally containing around 8–11 segments morphology and fruit characteristics may even (Loussert, 1992). be sufficient to confer the status of separate spe- The lime plant belongs to the kingdom cies for the acid and sweet types. All citrus fruits Plantae; phylum Magnoliophyta; class Magnoli- have nearly the same structure; however, the opsida; order Sapindales; family Rutaceae; genus elements that comprise these structures vary ac- Citrus; and species aurantifolia (Sethpakdee, cording to species and variety (Loussert, 1992). 1992). The three main types of lime largely cul- The external part of the rind consists of several tivated worldwide are Persian lime, Key lime morphologically different tissues called flavedo (Mexican lime) and Makrut lime (Table 1.1). Key because of the presence of flavonoid compounds limes are a small rounded fruit (Citrus aurantifolia (Ortiz, 2002). The whole surface of the fruit is (Christ.) Swingle), while the Persian limes bear a covered by polygonal cells to form the isodiamet- larger fruit (Citrus latifolia Tanaka) that is triploid ric layer. This layer contains cuticles that are and seedless. The Persian lime is the most fre- partially enclosed with a waxy substance to quently grown lime variety globally and México prevent excessive loss of water from the fruit. is one of the major producing countries. The A layer made of collenchyma and parenchyma fruit has an elliptical shape, thin, smooth skin cells is present under the layer of epidermis, and is juicy with an acidic lime aroma. Less heat where many oil glands containing essential oil is needed for Persian lime fruit maturity than for are located at different depths within the paren- Key limes, and they are more cold- and frost- chyma tissues. The white spongy part of the par- tolerant (Reuther et al., 1967). The Makrut lime enchyma, called the albedo, is located under the is produced in smaller amounts and is very layers of collenchyma and parenchyma (Ting popular in South-east Asian cookery. The fruit is and Attaway, 1971). The name albedo is derived small sized, the skin is rough and the leaves are from the Latin (albus = white) (Ortiz, 2002). The aromatic and used in cuisine (Reuther et al., 1967). *E-mail: [email protected] © CAB International 2017. The Lime: Botany, Production and Uses (eds M.M. Khan, R. Al-Yahyai and F. Al-Said) 1 2 M. Mumtaz Khan et al. The Key lime plant is spiny, less vigorous (A) (B) and less robust compared with Persian lime trees, and requires more heat for fruit develop- Juice vesicles ment. It produces smaller fruit when it is grown in the Mediterranean climate due to the sporadic Albedo cold snaps and lower temperature regimes (Reuther et al., 1967). On the other hand, it Carpel membrane grows vigorously in tropical environments and produces higher yields. Flavedo History, Origin and Distribution Fig. 1.1. Cross-section of lime fruit. (A) Persian lime, (B) Mexican. (Derived from Rivera-Cabrera It has been suggested that the lime perhaps et al., 2010.) evolved from a tri-hybrid cross amongst C. med- ica, C. grandis and a Microcitrus species (Barrett and Rhodes, 1976). However, another study re- Table 1.1. Description of major lime varieties. ported that mandarin was a parent of lime, Lime type Other names Appearance while another parent could be citron, pummelo or Papeda (Handa et al., 1986). Recent studies Key lime West Indian, 2.5–5 cm. have strongly argued that Key lime was a hybrid (Citrus × Bartenders, diameter, high of Papeda and Citron. The molecular evidence of auratifolia) Omani, acidity, strong these studies offered more conclusive informa- Mexican aroma, tart and bitter,7–8% tion compared with all previous studies reported citric acid relating to the origin of lime (Li et al., 2010). Like Persian lime Shiraz limoo, 5–12.7 cm. Key lime, ‘Tahiti’ lime is probably a tri-hybrid (Citrus × Tahitian, diameter, slight inter-generic cross of citron (C. medica), pummelo latifolia) Bearss nippled end, (C. grandis) and a Microcitrus species, C. micrantha (seedless) ripens to yellow (Moore, 2001). However, unlike Key lime, ‘Tahiti’ but sold green lime is a triploid. Makrut lime Kaffir 5 cm. diameter The ancestral place of lime origin is also (Citrus × rough bumpy controversial, similar to that of other citrus spe- hystrix) skin, thick rind, cies, but many researchers and historians be- aromatic leaves used in cooking lieve that lime originated from South-east Asia around 4000 BC and its native home is the Source: Reuther et al., 1967 Indo-Malayan region (Nicolosi et al., 2000). It is believed that the Europeans were not familiar The Key lime (Citrus aurantifolia (Christ.) with this fruit before the crusades, and it was Swingle), is a polyembryonic species, grown glo- Arab travellers who carried it to North Africa bally, generally in warm tropical to subtropical and the Near East. After the crusades it was regions such as India, México, the USA, Egypt taken to Palestine and then finally spread to and the West Indies (Morton, 1987). There are Mediterranean Europe (Cooper and Chapot, many common names used for Key lime, includ- 1977; Eckert and Eaks, 1989). During the mid- ing West Indian lime, Mexican lime, Egyptian dle of the thirteenth century, it was thought to lime, Bilolo and Dayap, etc. The Key lime (C. au- be cultivated in some parts of Italy, France, Spain rantifolia Swingle) is mostly known as tri-hybrid, and Portugal. It was introduced in México dur- evolved through an inter-generic cross (a three- ing the time of Spanish colonization. It is way hybrid where three plant species are in- strongly believed that both Portuguese and volved and at least two different genera) of citron Spanish voyagers took it to the Americas during (Citrus medica), pummelo (Citrus grandis) and a the early sixteenth century (Ziegler and Wolfe, Microcitrus species (Citrus micrantha). 1961). Once introduced as an exotic plant, it has Introduction and Overview of Lime 3 shown wide adaptation to diverse climates and 1990 (Al-Yahyai et al., 2012). Since its discovery was largely naturalized in México, the Carib- in the 1970s, the disease has spread to other bean, tropical areas of South America, Central countries in the Middle East, including the America and the Florida Keys. During 1839 its United Arab Emirates (UAE), Saudi Arabia and cultivation started to expand in Florida and it Iran, threatening many major lime-producing was developed as a common home yard fruit. By countries. 1883 it began to be produced on a small scale commercially in south-central Florida. A hurricane in 1906 along with soil nutri- ent depletion resulted in the pineapple culture Global Lime Production being abandoned. At that time, people began to plant limes as a substitute crop on the west coast Mexican lime is largely cultivated in tropical and of Florida. Lime fruit pickles became a prime subtropical areas of the globe. It is grown com- snack choice among schoolchildren in Boston. mercially, semi-commercially and in gardens. A small-scale lime pickle business was active Lime is cultivated on a range of continents all over from 1913 to 1923 but it crumbled in 1926 due the globe, particularly in Asia and the Americas to the devastating impact on lime groves of an- (Fig. 1.2a). Lime and lemon are mainly grown in other hurricane. Afterwards, the lime was India, México, China, Argentina, Brazil, the USA, largely grown as a common yard and garden Turkey, Spain, Iran and Italy (FAOSTAT, 2016). The plant in the Keys and the southern part of the percentage share of the top ten lime and lemon- Florida mainland. producing countries is presented in Fig. 1.2b. In the Middle East, lime is a major trad- The relationship between area planted and itional crop that has been used for a variety of production of the major lime-producing coun- culinary and medicinal purposes. Both fresh and tries becomes clearer regarding total area under dried limes are used for juice and as a condiment crop and the total harvest during 2013 upon for food flavouring. Historically, sun-dried limes examination of Fig. 1.3. Recognizing the im- were a major export commodity of Oman, and portance of lime and lemon for both domestic are frequently used in sauces and as a flavouring and industrial uses, their cultivation has been agent in other Arab cuisines. Oman is a leading increased considerably throughout the globe lime-producing country in the region. However, since 2000 (Fig. 1.4). lime production has been drastically reduced in It is noteworthy to observe the tremendous recent decades due to the spread of witches’ increase in yields, which may be attributed to broom disease of lime (WBDL), which has re- better plant material and the advancement in duced the cultivated area to less than half since technologically driven crop management. The (a) Africa (b) Oceania USA Turkey Europe 6% Brazil 0% 9% 7% 6% 7% Argentina Spain 11% 6% Iran Italy 5% 3% Asia 44% China India 16% 20% Americas 43% Mexico 17% Fig.