What type of acid is extracted from the juice of lemons, oranges, limes, and grapefruit?
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Acid Lemon Orange (fruit)
An acid is a molecule or ion capable of donating a hydron (proton or hydrogen ion H+), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid). 

The first category of acids is the proton donors or Brønsted acids. In the special case of aqueous solutions, proton donors form the hydronium ion H3O+ and are known as Arrhenius acids. Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents. A Brønsted or Arrhenius acid usually contains a hydrogen atom bonded to a chemical structure that is still energetically favorable after loss of H+. 

Aqueous Arrhenius acids have characteristic properties which provide a practical description of an acid.  Acids form aqueous solutions with a sour taste, can turn blue litmus red, and react with bases and certain metals (like calcium) to form salts. The word acid is derived from the Latin acidus/acēre meaning sour.  An aqueous solution of an acid has a pH less than 7 and is colloquially also referred to as 'acid' (as in 'dissolved in acid'), while the strict definition refers only to the solute. A lower pH means a higher acidity, and thus a higher concentration of positive hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic.

Common aqueous acids include hydrochloric acid (a solution of hydrogen chloride which is found in gastric acid in the stomach and activates digestive enzymes), acetic acid (vinegar is a dilute aqueous solution of this liquid), sulfuric acid (used in car batteries), and citric acid (found in citrus fruits). As these examples show, acids (in the colloquial sense) can be solutions or pure substances, and can be derived from acids (in the strict sense) that are solids, liquids, or gases. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid.

The second category of acids are Lewis acids, which form a covalent bond with an electron pair. An example is boron trifluoride (BF3), whose boron atom has a vacant orbital which can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia (NH3). Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons (H+) into the solution, which then accept electron pairs. However, hydrogen chloride, acetic acid, and most other Brønsted-Lowry acids cannot form a covalent bond with an electron pair and are therefore not Lewis acids.  Conversely, many Lewis acids are not Arrhenius or Brønsted-Lowry acids. In modern terminology, an acid is implicitly a Brønsted acid and not a Lewis acid, since chemists almost always refer to a Lewis acid explicitly as a Lewis acid. 

Definitions and concepts

Modern definitions are concerned with the fundamental chemical reactions common to all acids.

Most acids encountered in everyday life are aqueous solutions, or can be dissolved in water, so the Arrhenius and Brønsted-Lowry definitions are the most relevant.

The Brønsted-Lowry definition is the most widely used definition; unless otherwise specified, acid-base reactions are assumed to involve the transfer of a proton (H+) from an acid to a base.

Hydronium ions are acids according to all three definitions. Interestingly, although alcohols and amines can be Brønsted-Lowry acids, they can also function as Lewis bases due to the lone pairs of electrons on their oxygen and nitrogen atoms.

Arrhenius acids

The Swedish chemist Svante Arrhenius attributed the properties of acidity to hydrogen ions (H+) or protons in 1884. An Arrhenius acid is a substance that, when added to water, increases the concentration of H+ ions in the water.  Note that chemists often write H+(aq) and refer to the hydrogen ion when describing acid-base reactions but the free hydrogen nucleus, a proton, does not exist alone in water, it exists as the hydronium ion, H3O+. Thus, an Arrhenius acid can also be described as a substance that increases the concentration of hydronium ions when added to water. Examples include molecular substances such as HCl and acetic acid.

An Arrhenius base, on the other hand, is a substance which increases the concentration of hydroxide (OH−) ions when dissolved in water. This decreases the concentration of hydronium because the ions react to form H2O molecules:

H3O+(aq) + OH−(aq) ⇌ H2O(l) + H2O(l)

Due to this equilibrium, any increase in the concentration of hydronium is accompanied by a decrease in the concentration of hydroxide. Thus, an Arrhenius acid could also be said to be one that decreases hydroxide concentration, while an Arrhenius base increases it.

In an acidic solution, the concentration of hydronium ions is greater than 10−7 moles per liter. Since pH is defined as the negative logarithm of the concentration of hydronium ions, acidic solutions thus have a pH of less than 7.

Brønsted–Lowry acids

While the Arrhenius concept is useful for describing many reactions, it is also quite limited in its scope. In 1923 chemists Johannes Nicolaus Brønsted and Thomas Martin Lowry independently recognized that acid-base reactions involve the transfer of a proton. A Brønsted-Lowry acid (or simply Brønsted acid) is a species that donates a proton to a Brønsted-Lowry base. Brønsted-Lowry acid-base theory has several advantages over Arrhenius theory. Consider the following reactions of acetic acid (CH3COOH), the organic acid that gives vinegar its characteristic taste:

+    + 
+    + 

Both theories easily describe the first reaction: CH3COOH acts as an Arrhenius acid because it acts as a source of H3O+ when dissolved in water, and it acts as a Brønsted acid by donating a proton to water. In the second example CH3COOH undergoes the same transformation, in this case donating a proton to ammonia (NH3), but does not relate to the Arrhenius definition of an acid because the reaction does not produce hydronium. Nevertheless, CH3COOH is both an Arrhenius and a Brønsted-Lowry acid.

Brønsted-Lowry theory can be used to describe reactions of molecular compounds in nonaqueous solution or the gas phase. Hydrogen chloride (HCl) and ammonia combine under several different conditions to form ammonium chloride, NH4Cl. In aqueous solution HCl behaves as hydrochloric acid and exists as hydronium and chloride ions. The following reactions illustrate the limitations of Arrhenius's definition:
# H3O+(aq) + Cl−(aq) + NH3 → Cl−(aq) + NH4+(aq) + H2O
# HCl(benzene) + NH3(benzene) → NH4Cl(s)
# HCl(g) + NH3(g) → NH4Cl(s)

As with the acetic acid reactions, both definitions work for the first example, where water is the solvent and hydronium ion is formed by the HCl solute. The next two reactions do not involve the formation of ions but are still proton-transfer reactions. In the second reaction hydrogen chloride and ammonia (dissolved in benzene) react to form solid ammonium chloride in a benzene solvent and in the third gaseous HCl and NH3 combine to form the solid.

Lewis acids

A third, only marginally related concept was proposed in 1923 by Gilbert N. Lewis, which includes reactions with acid-base characteristics that do not involve a proton transfer. A Lewis acid is a species that accepts a pair of electrons from another species; in other words, it is an electron pair acceptor. Brønsted acid-base reactions are proton transfer reactions while Lewis acid-base reactions are electron pair transfers. Many Lewis acids are not Brønsted-Lowry acids. Contrast how the following reactions are described in terms of acid-base chemistry:
In the first reaction a fluoride ion, F−, gives up an electron pair to boron trifluoride to form the product tetrafluoroborate. Fluoride "loses" a pair of valence electrons because the electrons shared in the B—F bond are located in the region of space between the two atomic nuclei and are therefore more distant from the fluoride nucleus than they are in the lone fluoride ion. BF3 is a Lewis acid because it accepts the electron pair from fluoride. This reaction cannot be described in terms of Brønsted theory because there is no proton transfer. The second reaction can be described using either theory. A proton is transferred from an unspecified Brønsted acid to ammonia, a Brønsted base; alternatively, ammonia acts as a Lewis base and transfers a lone pair of electrons to form a bond with a hydrogen ion. The species that gains the electron pair is the Lewis acid; for example, the oxygen atom in H3O+ gains a pair of electrons when one of the H—O bonds is broken and the electrons shared in the bond become localized on oxygen. Depending on the context, a Lewis acid may also be described as an oxidizer or an electrophile. Organic Brønsted acids, such as acetic, citric, or oxalic acid, are not Lewis acids. They dissociate in water to produce a Lewis acid, H+, but at the same time also yield an equal amount of a Lewis base (acetate, citrate, or oxalate, respectively, for the acids mentioned). Few, if any, of the acids discussed in the following are Lewis acids.

Dissociation and equilibrium

Reactions of acids are often generalized in the form HA  H+ + A−, where HA represents the acid and A− is the conjugate base. This reaction is the protolysis. Acid-base conjugate pairs differ by one proton, and can be interconverted by the addition or removal of a proton (protonation and deprotonation, respectively). Note that the acid can be the charged species and the conjugate base can be neutral in which case the generalized reaction scheme could be written as HA+  H+ + A. In solution there exists an equilibrium between the acid and its conjugate base. The equilibrium constant K is an expression of the equilibrium concentrations of the molecules or the ions in solution. Brackets indicate concentration, such that [H2O] means the concentration of H2O. The acid dissociation constant Ka is generally used in the context of acid-base reactions. The numerical value of Ka is equal to the product of the concentrations of the products divided by the concentration of the reactants, where the reactant is the acid (HA) and the products are the conjugate base and H+.
K_a = \frac{[\mbox{H}^+] [\mbox{A}^-]}{[\mbox{HA}]}
The stronger of two acids will have a higher Ka than the weaker acid; the ratio of hydrogen ions to acid will be higher for the stronger acid as the stronger acid has a greater tendency to lose its proton. Because the range of possible values for Ka spans many orders of magnitude, a more manageable constant, pKa is more frequently used, where pKa = -log10 Ka. Stronger acids have a smaller pKa than weaker acids. Experimentally determined pKa at 25 °C in aqueous solution are often quoted in textbooks and reference material.

Nomenclature

In the classical naming system, acids are named according to their anions. That ionic suffix is dropped and replaced with a new suffix (and sometimes prefix), according to the table below.
For example, HCl has chloride as its anion, so the -ide suffix makes it take the form hydrochloric acid. In the IUPAC naming system, "aqueous" is simply added to the name of the ionic compound. Thus, for hydrogen chloride, the IUPAC name would be aqueous hydrogen chloride. The prefix "hydro-" is added only if the acid is made up of just hydrogen and one other element.

Classical naming system:

Acid strength

The strength of an acid refers to its ability or tendency to lose a proton. A strong acid is one that completely dissociates in water; in other words, one mole of a strong acid HA dissolves in water yielding one mole of H+ and one mole of the conjugate base, A−, and none of the protonated acid HA. In contrast, a weak acid only partially dissociates and at equilibrium both the acid and the conjugate base are in solution. Examples of strong acids are hydrochloric acid (HCl), hydroiodic acid (HI), hydrobromic acid (HBr), perchloric acid (HClO4), nitric acid (HNO3) and sulfuric acid (H2SO4). In water each of these essentially ionizes 100%. The stronger an acid is, the more easily it loses a proton, H+. Two key factors that contribute to the ease of deprotonation are the polarity of the H—A bond and the size of atom A, which determines the strength of the H—A bond. Acid strengths are also often discussed in terms of the stability of the conjugate base.

Stronger acids have a larger Ka and a more negative pKa than weaker acids.

Sulfonic acids, which are organic oxyacids, are a class of strong acids. A common example is toluenesulfonic acid (tosylic acid). Unlike sulfuric acid itself, sulfonic acids can be solids. In fact, polystyrene functionalized into polystyrene sulfonate is a solid strongly acidic plastic that is filterable.

Superacids are acids stronger than 100% sulfuric acid. Examples of superacids are fluoroantimonic acid, magic acid and perchloric acid. Superacids can permanently protonate water to give ionic, crystalline hydronium "salts". They can also quantitatively stabilize carbocations.

While Ka measures the strength of an acid compound, the strength of an aqueous acid solution is measured by pH, which is an indication of the concentration of hydronium in the solution.  The pH of a simple solution of an acid compound in water is determined by the dilution of the compound and the compound's Ka.

Chemical characteristics

Monoprotic acids

Monoprotic acids are those acids that are able to donate one proton per molecule during the process of dissociation (sometimes called ionization) as shown below (symbolized by HA):
HA(aq) + H2O(l)  H3O+(aq) + A−(aq)         Ka

Common examples of monoprotic acids in mineral acids include hydrochloric acid (HCl) and nitric acid (HNO3). On the other hand, for organic acids the term mainly indicates the presence of one carboxylic acid group and sometimes these acids are known as monocarboxylic acid. Examples in organic acids include formic acid (HCOOH), acetic acid (CH3COOH) and benzoic acid (C6H5COOH).

Polyprotic acids

Polyprotic acids, also known as polybasic acids, are able to donate more than one proton per acid molecule, in contrast to monoprotic acids that only donate one proton per molecule. Specific types of polyprotic acids have more specific names, such as diprotic acid (two potential protons to donate) and triprotic acid (three potential protons to donate).

A diprotic acid (here symbolized by H2A) can undergo one or two dissociations depending on the pH. Each dissociation has its own dissociation constant, Ka1 and Ka2.
:

The first dissociation constant is typically greater than the second; i.e., Ka1 > Ka2. For example, sulfuric acid (H2SO4) can donate one proton to form the bisulfate anion (HSO4−), for which Ka1 is very large; then it can donate a second proton to form the sulfate anion (SO42−), wherein the Ka2 is intermediate strength. The large Ka1 for the first dissociation makes sulfuric a strong acid. In a similar manner, the weak unstable carbonic acid (H2CO3) can lose one proton to form bicarbonate anion (HCO3−) and lose a second to form carbonate anion (CO32−). Both Ka values are small, but Ka1 > Ka2 .

A triprotic acid (H3A) can undergo one, two, or three dissociations and has three dissociation constants, where Ka1 > Ka2 > Ka3.
:
An inorganic example of a triprotic acid is orthophosphoric acid (H3PO4), usually just called phosphoric acid. All three protons can be successively lost to yield H2PO4−, then HPO42−, and finally PO43−, the orthophosphate ion, usually just called phosphate. Even though the positions of the three protons on the original phosphoric acid molecule are equivalent, the successive Ka values differ since it is energetically less favorable to lose a proton if the conjugate base is more negatively charged. An organic example of a triprotic acid is citric acid, which can successively lose three protons to finally form the citrate ion.

Although the subsequent loss of each hydrogen ion is less favorable, all of the conjugate bases are present in solution. The fractional concentration, α (alpha), for each species can be calculated. For example, a generic diprotic acid will generate 3 species in solution: H2A, HA−, and A2−. The fractional concentrations can be calculated as below when given either the pH (which can be converted to the [H+]) or the concentrations of the acid with all its conjugate bases:
\begin{align}
\alpha_\ce{H_2 A}&{\ce{[H^+]^2} \over {[\ce H^+]^2 + [\ce H^+]K_1 + K_1 K_2}}
 \ce
\\
\alpha_\ce{HA^- }&
 \ce
\\
\alpha_\ce{A^{2-}}&
 \ce
\end{align}

A plot of these fractional concentrations against pH, for given K1 and K2, is known as a Bjerrum plot. A pattern is observed in the above equations and can be expanded to the general n -protic acid that has been deprotonated i -times:

\alpha_{\ce H_{n-i} A^{i-} }= The lemon (Citrus × limon) is a species of small evergreen tree native to Asia.

The tree's ellipsoidal yellow fruit is used for culinary and non-culinary purposes throughout the world, primarily for its juice, which has both culinary and cleaning uses. The pulp and rind (zest) are also used in cooking and baking. The juice of the lemon is about 5% to 6% citric acid, which gives a sour taste. The distinctive sour taste of lemon juice makes it a key ingredient in drinks and foods such as lemonade and lemon meringue pie.

History

The origin of the lemon is unknown, though lemons are thought to have first grown in Assam (a region in northeast India), northern Burma or China.  A study of the genetic origin of the lemon reported it to be hybrid between bitter orange (sour orange) and citron. 

Lemons entered Europe near southern Italy no later than the first century AD, during the time of Ancient Rome. However, they were not widely cultivated. They were later introduced to Persia and then to Iraq and Egypt around 700 AD. The lemon was first recorded in literature in a 10th-century Arabic treatise on farming, and was also used as an ornamental plant in early Islamic gardens. It was distributed widely throughout the Arab world and the Mediterranean region between 1000 and 1150.

The first substantial cultivation of lemons in Europe began in Genoa in the middle of the 15th century. The lemon was later introduced to the Americas in 1493 when Christopher Columbus brought lemon seeds to Hispaniola on his voyages. Spanish conquest throughout the New World helped spread lemon seeds. It was mainly used as an ornamental plant and for medicine. In the 19th century, lemons were increasingly planted in Florida and California.

In 1747, James Lind's experiments on seamen suffering from scurvy involved adding lemon juice to their diets, though vitamin C was not yet known. 

The origin of the word "lemon" may be Middle Eastern. The word draws from the Old French limon, then Italian limone, from the Arabic laymūn or līmūn, and from the Persian līmūn, a generic term for citrus fruit, which is a cognate of Sanskrit (nimbū, “lime”). 

Varieties

The 'Bonnie Brae' is oblong, smooth, thin-skinned, and seedless;  mostly grown in San Diego County. 

The 'Eureka' grows year-round and abundantly. This is the common supermarket lemon,  also known as 'Four Seasons' (Quatre Saisons) because of its ability to produce fruit and flowers together throughout the year. This variety is also available as a plant to domestic customers.  There is also a pink-fleshed Eureka lemon, which's outer skin is variegated from green and yellow stripes. 

The 'Femminello St. Teresa', or 'Sorrento'  is native to Italy. This fruit's zest is high in lemon oils. It is the variety traditionally used in the making of limoncello.

The 'Meyer' is a cross between a lemon and possibly an orange or a mandarin, and was named after Frank N. Meyer, who first introduced it to the USA in 1908. Thin-skinned and slightly less acidic than the Lisbon and Eureka lemons, Meyer lemons require more care when shipping and are not widely grown on a commercial basis. Meyer lemons often mature to a yellow-orange color. They are slightly more frost-tolerant than other lemons.

The 'Ponderosa' is more cold-sensitive than true lemons; the fruit are thick-skinned and very large. It is likely a citron-lemon hybrid.

The 'Yen Ben' is an Australasian cultivar. 

Culinary uses

Lemon juice, rind, and zest are used in a wide variety of foods and drinks. Lemon juice is used to make lemonade, soft drinks, and cocktails. It is used in marinades for fish, where its acid neutralizes amines in fish by converting them into nonvolatile ammonium salts, and meat, where the acid partially hydrolyzes tough collagen fibers, tenderizing the meat, but the low pH denatures the proteins, causing them to dry out when cooked. Lemon juice is frequently used in the United Kingdom to add to pancakes, especially on Shrove Tuesday.

Lemon juice is also used as a short-term preservative on certain foods that tend to oxidize and turn brown after being sliced (enzymatic browning), such as apples, bananas, and avocados, where its acid denatures the enzymes.

Lemon juice and rind are used to make marmalade, lemon curd and lemon liqueur. Lemon slices and lemon rind are used as a garnish for food and drinks. Lemon zest, the grated outer rind of the fruit, is used to add flavor to baked goods, puddings, rice, and other dishes.

The leaves of the lemon tree are used to make a tea and for preparing cooked meats and seafoods.

Other uses

Industrial

Lemons were the primary commercial source of citric acid before the development of fermentation-based processes. 

As a cleaning agent

The juice of the lemon may be used for cleaning. A halved lemon dipped in salt or baking powder is used to brighten copper cookware. The acid dissolves the tarnish and the abrasives assist the cleaning. As a sanitary kitchen deodorizer the juice can deodorize, remove grease, bleach stains, and disinfect; when mixed with baking soda, it removes stains from plastic food storage containers.  The oil of the lemon's peel also has various uses. It is used as a wood cleaner and polish, where its solvent property is employed to dissolve old wax, fingerprints, and grime. Lemon oil and orange oil are also used as a nontoxic insecticide treatment.

A halved lemon is used as a finger moistener for those counting large amounts of bills, such as tellers and cashiers.

Medicinal

Lemon oil may be used in aromatherapy. Lemon oil aroma does not influence the human immune system, but may enhance mood. 
The low pH of juice makes it antibacterial, and in India, the lemon is used in Indian traditional medicines (Siddha medicine and Ayurveda).

Other

One educational science experiment involves attaching electrodes to a lemon and using it as a battery to produce electricity. Although very low power, several lemon batteries can power a small digital watch.  These experiments also work with other fruits and vegetables.

Lemon juice may be used as a simple invisible ink, developed by heat.

Lemon alternatives

Many plants taste or smell similar to lemons.
* Certain cultivars of basil
* Cymbopogon (lemongrass)
* Lemon balm, a mint-like herbaceous perennial in the Lamiaceae family
* Two varieties of scented geranium: Pelargonium crispum (lemon geranium) and Pelargonium x melissinum (lemon balm)
* Lemon thyme
* Lemon verbena
* Limes, another common sour citrus fruit, used similarly to lemons
* Certain cultivars of mint
* Magnolia grandiflora tree flowers

Production

In 2013, world production of lemons (data combined with limes) was 15.2 million tonnes, led by India, Mexico and China as the main producers (table). Argentina and Brazil also had significant production (table).

Nutritional value and phytochemicals

Lemons are a rich source of vitamin C, providing 64% of the Daily Value in a 100 g serving (table). Other essential nutrients, however, have insignificant content (table).

Lemons contain numerous phytochemicals, including polyphenols and terpenes.  As with other citrus fruits, they have significant concentrations of citric acid (about 47 g/l in juice). 

Gallery

File:Lemon-citrus limon seedling.jpg|Lemon seedling
File:Citrus limon - Lemon tree - Limonero - Limoeiro.JPG|Full sized tree
File:Citrus fruits on tree.jpg|Green and yellow lemons in growth
File:Citrus x limon 'Variegated Pink' - Lemon.jpg|Variegated pink lemon The orange (specifically, the sweet orange) is the fruit of the citrus species Citrus × sinensis in the family Rutaceae.

The fruit of the Citrus × sinensis is considered a sweet orange, whereas the fruit of the Citrus × aurantium is considered a bitter orange. The sweet orange reproduces asexually (apomixis through nucellar embryony); varieties of sweet orange arise through mutations.

The orange is a hybrid, between pomelo (Citrus maxima) and mandarin (Citrus reticulata). It has genes that are ~25% pomelo and ~75% mandarin;  however, it is not a simple backcrossed BC1 hybrid, but hybridized over multiple generations. The chloroplast genes, and therefore the maternal line, seem to be pomelo. The sweet orange has had its full genome sequenced. Earlier estimates of the percentage of pomelo genes varying from ~50% to 6% have been reported.

Sweet oranges were mentioned in Chinese literature in 314 BC. , orange trees were found to be the most cultivated fruit tree in the world.Morton, J., [http://www.hort.purdue.edu/newcrop/morton/orange.html Fruits of Warm Climates] (1987) Miami, FL, pp. 134–142. Orange trees are widely grown in tropical and subtropical climates for their sweet fruit. The fruit of the orange tree can be eaten fresh, or processed for its juice or fragrant peel.  , sweet oranges accounted for approximately 70% of citrus production. 

In 2013, 71.4 million metric tons of oranges were grown worldwide, production being highest in Brazil and the U.S. states of Florida and California. 

Botanical information and terminology 

All citrus trees belong to the single genus Citrus and remain almost entirely interfertile. This means that there is only one superspecies that includes grapefruits, lemons, limes, oranges, and various other types and hybrids.  As the interfertility of oranges and other citrus has produced numerous hybrids and cultivars, and bud mutations have also been selected, their taxonomy is fairly controversial, confusing or inconsistent.  The fruit of any citrus tree is considered a hesperidium, a kind of modified berry; it is covered by a rind originated by a rugged thickening of the ovary wall.  

Different names have been given to the many varieties of the genus. Orange applies primarily to the sweet orange – Citrus sinensis (L.) Osbeck. The orange tree is an evergreen, flowering tree, with an average height of 9 to, although some very old specimens can reach 15 m. Its oval leaves, alternately arranged, are 4 to long and have crenulate margins.  Although the sweet orange presents different sizes and shapes varying from spherical to oblong, it generally has ten segments (carpels) inside, and contains up to six seeds (or pips)  and a porous white tissue – called pith or, more properly, mesocarp or albedo—lines its rind.  When unripe, the fruit is green. The grainy irregular rind of the ripe fruit can range from bright orange to yellow-orange, but frequently retains green patches or, under warm climate conditions, remains entirely green. Like all other citrus fruits, the sweet orange is non-climacteric. The Citrus sinensis is subdivided into four classes with distinct characteristics: common oranges, blood or pigmented oranges, navel oranges, and acidless oranges.Home Fruit Production – Oranges, Julian W. Sauls, Ph.D., Professor & Extension Horticulturist, Texas Cooperative Extension (December, 1998), [http://aggie-horticulture.tamu.edu/citrus/oranges.htm aggie-horticulture.tamu.edu]

Other citrus groups also known as oranges are:
* Bitter orange (Citrus aurantium), also known as Seville orange, sour orange (especially when used as rootstock for a sweet orange tree), bigarade orange and marmalade orange. Like the sweet orange, it is a pomelo x mandarin hybrid. 
* Bergamot orange (Citrus bergamia Risso), grown mainly in Italy for its peel, producing  a primary essence for perfumes, also used to flavor Earl Grey tea. It is a hybrid, probably bitter orange x limetta. 
* Trifoliate orange (Poncirus trifoliata), sometimes included in the genus (classified as Citrus trifoliata). It often serves as a rootstock for sweet orange trees and other Citrus cultivars.
* Mandarin orange (Citrus reticulata) is an original species of citrus, and is a progenitor of the common orange.

An enormous number of cultivars have, like the sweet orange, a mix of pomelo and mandarin ancestry. Some cultivars are mandarin-pomelo hybrids, bred from the same parents as the sweet orange (e.g. the tangor and ponkan tangerine). Other cultivars are sweet orange x mandarin hybrids (e.g. clementines). Mandarin traits generally include being smaller and oblate, easier to peel, and less acidic.  Pomelo traits include a thick white albedo (rind pith, mesocarp) that is more closely attached to the segments.

Orange trees generally are grafted. The bottom of the tree, including the roots and trunk, is called rootstock, while the fruit-bearing top has two different names: budwood (when referring to the process of grafting) and scion (when mentioning the variety of orange). 

Etymology 

The word orange derives from the Sanskrit word for "orange tree" (नारङ्ग nāraṅga), which is probably of Dravidian origin.  The Sanskrit word reached European languages through Persian نارنگ (nārang) and its Arabic derivative  نارنج (nāranj).

The word entered Late Middle English in the fourteenth century via Old French orenge (in the phrase pomme d'orenge).  The French word, in turn, comes from Old Provençal auranja, based on Arabic nāranj. In several languages, the initial n present in earlier forms of the word dropped off because it may have been mistaken as part of an indefinite article ending in an n sound—in French, for example, une norenge may have been heard as une orenge. This linguistic change is called juncture loss. The color was named after the fruit,  and the first recorded use of orange as a color name in English was in 1512.  

As Portuguese merchants were presumably the first to introduce the sweet orange in Europe, in several modern Indo-European languages the fruit has been named after them. Some examples are Albanian portokall, Bulgarian портокал (portokal), Greek πορτοκάλι (portokali), Macedonian ', Persian پرتقال (porteghal), and Romanian portocală.   Related names can be found in other languages, such as Arabic البرتقال (bourtouqal), Georgian ფორთოხალი (p'ort'oxali), Turkish portakal and Amharic birtukan. Also, in southern Italian dialects (e.g. Neapolitan), an orange is portogallo or purtuallo, literally "(the) Portuguese (one)", in contrast to standard Italian arancia.

In other Indo-European languages, the words for orange allude to the eastern origin of the fruit and can be translated literally as "apple from China". Some examples are Low German Apfelsine, Dutch appelsien and sinaasappel, Swedish apelsin, and Norwegian appelsin. A similar case is Puerto Rican Spanish china.  

Various Slavic languages use the variants pomaranč (Slovak), pomeranč (Czech), pomaranča (Slovene), and pomarańcza (Polish), all from Old French pomme d'orenge.  

Varieties 

Common oranges 

Common oranges (also called "white", "round", or "blond" oranges) constitute about two-thirds of all the orange production. The majority of this crop is used mostly for juice extraction.

Valencia 

The Valencia orange is a late-season fruit, and therefore a popular variety when navel oranges are out of season. This is why an anthropomorphic orange was chosen as the mascot for the 1982 FIFA World Cup, held in Spain. The mascot was named Naranjito ("little orange") and wore the colors of the Spanish national football team.

Hart's Tardiff Valencia 

Thomas Rivers, an English nurseryman, imported this variety from the Azores Islands and catalogued it in 1865 under the name Excelsior. Around 1870, he provided trees to S. B. Parsons, a Long Island nurseryman, who in turn sold them to E. H. Hart of Federal Point, Florida.

Hamlin 

This cultivar was discovered by A. G. Hamlin near Glenwood, Florida, in 1879. The fruit is small, smooth, not highly colored, and juicy, with a pale yellow colored juice, especially in fruits that come from lemon rootstock. The fruit may be seedless, or may contain a number of small seeds.  The tree is high-yielding and cold-tolerant and it produces good quality fruit, which is harvested from October to December. It thrives in humid subtropical climates. In cooler, more arid areas, the trees produce edible fruit, but too small for commercial use.

Trees from groves in hammocks or areas covered with pine forest are budded on sour orange trees, a method that gives a high solids content. On sand, they are grafted on rough lemon rootstock. The Hamlin orange is one of the most popular juice oranges in Florida and replaces the Parson Brown variety as the principal early-season juice orange. This cultivar is now the leading early orange in Florida and, possibly, in the rest of the world. 

Other varieties of common oranges 

* Belladonna: grown in Italy
* Berna: grown mainly in Spain
* Biondo Comune ("ordinary blond"): widely grown in the Mediterranean basin, especially in North Africa, Egypt, Greece (where it is called "koines"), Italy (where it is also known as "Liscio"), and Spain; it also is called "Beledi" and "Nostrale"; in Italy, this variety ripens in December, earlier than the competing Tarocco variety 
* Biondo Riccio: grown in Italy
* Cadanera: a seedless orange of excellent flavor grown in Algeria, Morocco, and Spain; it begins to ripen in November and is known by a wide variety of trade names, such as Cadena Fina, Cadena sin Jueso, Precoce de Valence ("early from Valencia"), Precoce des Canaries, and Valence san Pepins ("seedless Valencia"); it was first grown in Spain in 1870 
* Calabrese or Calabrese Ovale: grown in Italy
* Carvalhal: grown in Portugal
* Castellana: grown in Spain
* Cherry Orange: grown in southern China and Japan
* Clanor: grown in South Africa
* Dom João: grown in Portugal
* Fukuhara: grown in Japan
* Gardner: grown in Florida, this mid-season orange ripens around the beginning of February, approximately the same time as the Midsweet variety; Gardner is about as hardy as Sunstar and Midsweet
* Homosassa: grown in Florida
* Jaffa orange: grown in the Middle East, also known as "Shamouti"
* Jincheng: the most popular orange in China
* Joppa: grown in South Africa and Texas
* Khettmali: grown in Israel and Lebanon

* Kona: a type of Valencia orange introduced in Hawaii in 1792 by Captain George Vancouver; for many decades in the nineteenth century, these oranges were the leading export from the Kona district on the Big Island of Hawaii; in Kailua-Kona, some of the original stock still bears fruit
* Lue Gim Gong: grown in Florida, is an early scion developed by Lue Gim Gong, a Chinese immigrant known as the "Citrus Genius"; in 1888, Lue cross-pollinated two orange varieties – the Hart's late Valencia and the Mediterranean Sweet – and obtained a fruit both sweet and frost-tolerant; this variety was propagated at the Glen St. Mary Nursery, which in 1911 received the Silver Wilder Medal by the American Pomological Society;  originally considered a hybrid, the Lue Gim Gong orange was later found to be a nucellar seedling of the Valencia type,  which is properly called Lue Gim Gong; since 2006, the Lue Gim Gong variety is grown in Florida, although sold under the general name Valencia
* Macetera: grown in Spain, it is known for its unique flavor

* Malta: grown in Pakistan
* Maltaise Blonde: grown in north Africa
* Maltaise Ovale: grown in South Africa and in California under the names of Garey's or California Mediterranean Sweet
* Marrs: grown in Texas, California and Iran, it is relatively low in acid
* Midsweet: grown in Florida, it is a newer scion similar to the Hamlin and Pineapple varieties, it is hardier than Pineapple and ripens later; the fruit production and quality are similar to those of the Hamlin, but the juice has a deeper color
* Moro Tarocco: grown in Italy, it is oval, resembles a tangelo, and has a distinctive caramel-colored endocarp; this color is the result of a pigment called anthocarpium, not usually found in citruses, but common in red fruits and flowers; the original mutation occurred in Sicily in the seventeenth century
* Mosambi: grown in India and Pakistan, it is so low in acid and insipid that it might be classified as acidless
* Narinja: grown in Andhra, South India
* Parson Brown: grown in Florida, Mexico, and Turkey, it once was a widely-grown Florida juice orange, its popularity has declined since new varieties with more juice, better yield, and higher acid and sugar content have been developed; it originated as a chance seedling in Florida in 1865; its fruits are round, medium large, have a thick, pebbly peel and contain 10 to 30 seeds; it still is grown because it is the earliest maturing fruit in the United States, usually maturing in early September in the Valley district of Texas, and from early October to January in Florida;Ferguson, James J. [http://web.archive.org/web/20100203161504/http://edis.ifas.ufl.edu/hs123 Your Florida Dooryard Citrus Guide – Appendices, Definitions and Glossary]. edis.ifas.ufl.edu its peel and juice color are poor, as is the quality of its juice
* Pera: grown in Brazil, it is very popular in the Brazilian citrus industry and yielded 7.5 million metric tons in 2005
* Pera Coroa: grown in Brazil
* Pera Natal: grown in Brazil
* Pera Rio: grown in Brazil
* Pineapple: grown in North and South America and India
* Premier: grown in South Africa
* Rhode Red: is a mutation of the Valencia orange, but the color of its flesh is more intense; it has more juice, and less acidity and vitamin C than the Valencia; it was discovered by Paul Rhode in 1955 in a grove near Sebring, Florida
* Roble: it was first shipped from Spain in 1851 by Joseph Roble to his homestead in what is now Roble's Park in Tampa, Florida; it is known for its high sugar content
* Queen: grown in South Africa
* Salustiana: grown in North Africa
* Sathgudi: grown in Tamil Nadu, South India
* Seleta, Selecta: grown in Australia and Brazil, it is high in acid
* Shamouti Masry: grown in Egypt; it is a richer variety of Shamouti
* Sunstar: grown in Florida, this newer cultivar ripens in mid-season (December to March) and it is more resistant to cold and fruit-drop than the competing Pineapple variety; the color of its juice is darker than that of the competing Hamlin
* Tomango: grown in South Africa
* Verna: grown in Algeria, Mexico, Morocco, and Spain
* Vicieda: grown in Algeria, Morocco, and Spain
* Westin: grown in Brazil
* Xã Đoài orange: grown in Vietnam

Navel oranges 

Navel oranges are characterized by the growth of a second fruit at the apex, which protrudes slightly and resembles a human navel. They are primarily grown for human consumption for various reasons: their thicker skin makes them easy to peel, they are less juicy and their bitterness – a result of the high concentrations of limonin and other limonoids –  renders them less suitable for juice. Their widespread distribution and long growing season have made navel oranges very popular. In the United States, they are available from November to April, with peak supplies in January, February, and March. 

According to a 1917 study by Palemon Dorsett, Archibald Dixon Shamel and Wilson Popenoe of the United States Department of Agriculture (USDA), a single mutation in a Selecta orange tree planted on the grounds of a monastery near Bahia, Brazil, probably yielded the first navel orange between 1810 and 1820. Nevertheless, a researcher at the University of California, Riverside, has suggested that the parent variety was more likely the Portuguese navel orange (Umbigo), described by Antoine Risso and Pierre Antoine Poiteau in their book Histoire naturelle des orangers ("Natural History of Orange Trees", 1818–1822). The mutation caused the orange to develop a second fruit at its base, opposite the stem, embedded within the peel of the primary orange.  Navel oranges were introduced in Australia in 1824 and in Florida in 1835. In 1870, twelve cuttings of the original tree were transplanted to Riverside, California, where the fruit became known as "Washington".  This cultivar was very successful, and rapidly spread to other countries. Because the mutation left the fruit seedless and, therefore, sterile, the only method to cultivate navel oranges was to graft cuttings onto other varieties of citrus trees. The California Citrus State Historic Park and the Orcutt Ranch Horticulture Center preserve the history of navel oranges in Riverside.

Today, navel oranges continue to be propagated through cutting and grafting. This does not allow for the usual selective breeding methodologies, and so all navel oranges can be considered fruits from that single, nearly two-hundred-year-old tree: they have exactly the same genetic make-up as the original tree and are, therefore, clones. This case is similar to that of the common yellow seedless banana, the Cavendish, or that of the Granny Smith apple. On rare occasions, however, further mutations can lead to new varieties. 

Cara cara navels 

Cara cara oranges (also called "red navel") are a type of navel orange grown mainly in Venezuela, South Africa and in California's San Joaquin Valley. They are sweet and comparatively low in acid,  with a bright orange rind similar to that of other navels, but their flesh is distinctively pinkish red. It is believed that they have originated as a cross between the Washington navel and the Brazilian Bahia navel,  and they were discovered at the Hacienda Cara Cara in Valencia, Venezuela, in 1976.[http://www.citrusvariety.ucr.edu/citrus/caracara.html Cara Cara navel orange]. University of California, Riverside

South African cara caras are ready for market in early August, while Venezuelan fruits arrive in October and Californian fruits in late November.

Other varieties of navels 

* Bahianinha or Bahia
* Dream Navel
* Late Navel
* Washington or California Navel

Blood oranges 

Blood oranges are a natural mutation of C. sinensis, although today the majority of them are hybrids. High concentrations of anthocyanin give the rind, flesh, and juice of the fruit their characteristic dark red color. Blood oranges were first discovered and cultivated in Sicily in the fifteenth century. Since then they have spread worldwide, but are grown especially in Spain and Italy under the names of sanguina and sanguinella, respectively.

The blood orange, with its distinct color and flavor, is generally considered the most delicious juice orange, and has found a niche as an ingredient variation in traditional Seville marmalade.

Other varieties of blood oranges 

* Maltese: a small and highly colored variety, generally thought to have originated in Italy as a mutation and cultivated there for centuries. It also is grown extensively in southern Spain and Malta. It is used in sorbets and other desserts due to its rich burgundy color.
* Moro: originally from Sicily, it is common throughout Italy. This medium-sized fruit has a relatively long harvest, which lasts from December to April.
* Sanguinelli: a mutant of the Doble Fina, discovered in 1929 in Almenara, in the Castellón province of Spain. It is cultivated in Sicily.
* Scarlet navel: a variety with the same mutation as the navel orange.
* Tarocco: a relatively new variety developed in Italy. It begins to ripen in late January.

Acidless oranges 

Acidless oranges are an early-season fruit with very low levels of acid. They also are called "sweet" oranges in the United States, with similar names in other countries: douce in France, sucrena in Spain, dolce or maltese in Italy, meski in North Africa and the Near East (where they are especially popular), şeker portakal ("sugar orange") in Turkey,  succari in Egypt, and lima in Brazil.

The lack of acid, which protects orange juice against spoilage in other groups, renders them generally unfit for processing as juice, so they are primarily eaten. They remain profitable in areas of local consumption, but rapid spoilage renders them unsuitable for export to major population centres of Europe, Asia, or the United States.

Attributes 

Nutritional value and phytochemicals 

As with other citrus fruits, orange pulp is an excellent source of vitamin C, providing 64% of the Daily Value in a 100 g serving (right table). Numerous other essential nutrients are present in low amounts (right table).

Oranges contain diverse phytochemicals, including carotenoids (beta-carotene, lutein and beta-cryptoxanthin), flavonoids (e.g. naringenin)  and numerous volatile organic compounds producing orange aroma, including aldehydes, esters, terpenes, alcohols, and ketones. 

Acidity 

Being a citrus fruit, the orange is acidic: its pH levels are as low as 2.9,  and as high as 4.0. 

Grading 

The United States Department of Agriculture (USDA) has established the following grades for Florida oranges, which primarily apply to oranges sold as fresh fruit: US Fancy, US No. 1 Bright, US No. 1, US No. 1 Golden, US No. 1 Bronze, US No. 1 Russet, US No. 2 Bright, US No. 2, US No. 2 Russet, and US No. 3.[http://web.archive.org/web/20110726100358/http://www.ams.usda.gov/AMSv1.0/getfile?dDocName
STELPRDC5050382 United States Standards for Grades of Florida Oranges and Tangelos] (USDA; February, 1997) The general characteristics graded are color (both hue and uniformity), firmness, maturity, varietal characteristics, texture, and shape. Fancy, the highest grade, requires the highest grade of color and an absence of blemishes, while the terms Bright, Golden, Bronze, and Russet concern solely discoloration.

Grade numbers are determined by the amount of unsightly blemishes on the skin and firmness of the fruit that do not affect consumer safety. The USDA separates blemishes into three categories:
# General blemishes: ammoniation, buckskin, caked melanose, creasing, decay, scab, split navels, sprayburn, undeveloped segments, unhealed segments, and wormy fruit
# Injuries to fruit: bruises, green spots, oil spots, rough, wide, or protruding navels, scale, scars, skin breakdown, and thorn scratches
# Damage caused by dirt or other foreign material, disease, dryness, or mushy condition, hail, insects, riciness or woodiness, and sunburn.

The USDA uses a separate grading system for oranges used for juice because appearance and texture are irrelevant in this case. There are only two grades: US Grade AA Juice and US Grade A Juice, which are given to the oranges before processing. Juice grades are determined by three factors:
# The juiciness of the orange
# The amount of solids in the juice (at least 10% solids are required for the AA grade)
# The proportion of anhydric citric acid in fruit solids

History 

The orange is unknown in the wild state; it is assumed to have originated in southern China, northeastern India, and perhaps southeastern Asia, and that they were first cultivated in China around 2500 BC. 

In Europe, citrus fruits—among them the bitter orange, introduced to Italy by the crusaders in the 11th century—were grown widely in the south for medicinal purposes, but the sweet orange was unknown until the late 15th century or the beginnings of the 16th century, when Italian and Portuguese merchants brought orange trees into the Mediterranean area. Shortly afterward, the sweet orange quickly was adopted as an edible fruit. It also was considered a luxury item and wealthy people grew oranges in private conservatories, called orangeries. By 1646, the sweet orange was well known throughout Europe.

Spanish travelers introduced the sweet orange into the American continent. On his second voyage in 1493, Christopher Columbus may have planted the fruit in Hispaniola.  Subsequent expeditions in the mid-1500s brought sweet oranges to South America and Mexico, and to Florida in 1565, when Pedro Menéndez de Avilés founded St Augustine. Spanish missionaries brought orange trees to Arizona between 1707 and 1710, while the Franciscans did the same in San Diego, California, in 1769. An orchard was planted at the San Gabriel Mission around 1804 and a commercial orchard was established in 1841 near present-day Los Angeles. In Louisiana, oranges were probably introduced by French explorers.

Archibald Menzies, the botanist and naturalist on the Vancouver Expedition, collected orange seeds in South Africa, raised the seedlings onboard and gave them to several Hawaiian chiefs in 1792. Eventually, the sweet orange was grown in wide areas of the Hawaiian Islands, but its cultivation stopped after the arrival of the Mediterranean fruit fly in the early 1900s. 

As oranges are rich in vitamin C and do not spoil easily, during the Age of Discovery, Portuguese, Spanish, and Dutch sailors planted citrus trees along trade routes to prevent scurvy.

Around 1872, Florida farmers obtained seeds from New Orleans. Many orange groves were established by grafting the sweet orange on to sour orange rootstocks.

Cultivation 

Climate 

Like most citrus plants, oranges do well under moderate temperatures—between —and require considerable amounts of sunshine and water. It has been suggested the use of water resources by the citrus industry in the Middle East is a contributing factor to the desiccation of the region. Another significant element in the full development of the fruit is the temperature variation between summer and winter and, between day and night. In cooler climates, oranges can be grown indoors.

As oranges are sensitive to frost, there are different methods to prevent frost damage to crops and trees when subfreezing temperatures are expected. A common process is to spray the trees with water so as to cover them with a thin layer of ice that will stay just at the freezing point, insulating them even if air temperatures drop far lower. This is because water continues to lose heat as long as the environment is colder than it is, and so the water turning to ice in the environment cannot damage the trees. This practice, however, offers protection only for a very short time.  Another procedure is burning fuel oil in smudge pots put between the trees. These devices burn with a great deal of particulate emission, so condensation of water vapour on the particulate soot prevents condensation on plants and raises the air temperature very slightly. Smudge pots were developed for the first time after a disastrous freeze in Southern California in January 1913 destroyed a whole crop.

Propagation 

It is possible to grow orange trees directly from seeds, but they may be infertile or produce fruit that may be different from its parent. For the seed of a commercial orange to grow, it must be kept moist at all times. One approach is placing the seeds between two sheets of damp paper towel until they germinate and then planting them, although many cultivators just set the seeds straight into the soil.

Commercially grown orange trees are propagated asexually by grafting a mature cultivar onto a suitable seedling rootstock to ensure the same yield, identical fruit characteristics, and resistance to diseases throughout the years. Propagation involves two stages: first, a rootstock is grown from seed. Then, when it is approximately one year old, the leafy top is cut off and a bud taken from a specific scion variety, is grafted into its bark. The scion is what determines the variety of orange, while the rootstock makes the tree resistant to pests and diseases and adaptable to specific soil and climatic conditions. Thus, rootstocks influence the rate of growth and have an effect on fruit yield and quality. 

Rootstocks must be compatible with the variety inserted into them because otherwise, the tree may decline, be less productive, or die.

Among the several advantages to grafting are that trees mature uniformly and begin to bear fruit earlier than those reproduced by seeds (3 to 4 years in contrast with 6 to 7 years),  and that it makes it possible to combine the best attributes of a scion with those of a rootstock. 

Harvest 

Canopy-shaking mechanical harvesters are being used increasingly in Florida to harvest oranges. Current canopy shaker machines use a series of six-to-seven-foot long tines to shake the tree canopy at a relatively constant  stroke and frequency. 

Normally, oranges are picked once they are pale orange. 

Degreening 

Oranges must be mature when harvested. In the United States, laws forbid harvesting immature fruit for human consumption in Texas, Arizona, California and Florida.  Ripe oranges, however, often have some green or yellow-green color in the skin. Ethylene gas is used to turn green skin to orange. This process is known as "degreening", also called "gassing", "sweating", or "curing". Oranges are non-climacteric fruits and cannot post-harvest ripen internally in response to ethylene gas, though they will de-green externally. 

Storage 

Commercially, oranges can be stored by refrigeration in controlled-atmosphere chambers for up to 12 weeks after harvest. Storage life ultimately depends on cultivar, maturity, pre-harvest conditions, and handling.  In stores and markets, however, oranges should be displayed on non-refrigerated shelves.

At home, oranges have a shelf life of about one month.[http://www.cpma.ca/Files/CPMA.HomeStorageGuide.English.pdf Home Storage Guide for Fresh Fruits & Vegetables. Canadian Produce Marketing Association] In either case, optimally, they are stored loosely in an open or perforated plastic bag.

Pests and diseases 

Cottony cushion scale 

The first major pest that attacked orange trees in the United States was the cottony cushion scale (Icerya purchasi), imported from Australia to California in 1868. Within 20 years, it wiped out the citrus orchards around Los Angeles, and limited orange growth throughout California. In 1888, the USDA sent Alfred Koebele to Australia to study this scale insect in its native habitat. He brought back with him specimens of Novius cardinalis, an Australian ladybird beetle, and within a decade the pest was controlled.

Citrus greening disease 

The citrus greening disease, caused by the bacterium Liberobacter asiaticum, has been the most serious threat to orange production since 2010. It is characterized by streaks of different shades on the leaves, and deformed, poorly-colored, unsavory fruit. In areas where the disease is endemic, citrus trees live for only five to eight years and never bear fruit suitable for consumption. In the western hemisphere, the disease was discovered in Florida in 1998, where it has attacked nearly all the trees ever since. It was reported in Brazil by Fundecitrus Brasil in 2004.Asian Citrus Psllids (Sternorryncha: Psyllidae) and Greening Disease of Citrus, by Susan E. Halbert and Keremane L. Manjunath, Florida Entomologist (Abstract. September 2004) p. 330 [http://www.fcla.edu/FlaEnt/fe87p330.pdf FCLA.edu] As from 2009, 0.87% of the trees in Brazil's main orange growing areas (São Paulo and Minas Gerais) showed symptoms of greening, an increase of 49% over 2008.[http://gain.fas.usda.gov/Recent%20GAIN%20Publications/Commodity%20Report_CITRUS%20SEMI-ANNUAL_Sao%20Paulo%20ATO_Brazil_6-18-2009.pdf GAIN Report Number: BR9006], USDA Foreign Agricultural Service (June, 2009)

The disease is spread primarily by two species of psyllid insects. One of them is the Asian citrus psyllid (Diaphorina citri Kuwayama), an efficient vector of the Liberobacter asiaticum. Generalist predators such as the ladybird beetles Curinus coeruleus, Olla v-nigrum, Harmonia axyridis, and Cycloneda sanguinea, and the lacewings Ceraeochrysa spp. and Chrysoperla spp. make significant contribution to the mortality of the Asian citrus psyllid, which results in 80–100% reduction in psyllid populations. In contrast, parasitism by Tamarixia radiata, a species-specific parasitoid of the Asian citrus psyllid, is variable and generally low in southwest Florida: in 2006, it amounted to a reduction of less than 12% from May to September and 50% in November.

In 2007, foliar applications of insecticides reduced psyllid populations for a short time, but also suppressed the populations of predatory ladybird beetles. Soil application of aldicarb provided limited control of Asian citrus psyllid, while drenches of imidacloprid to young trees were effective for two months or more. 

Management of citrus greening disease is difficult and requires an integrated approach that includes use of clean stock, elimination of inoculum via voluntary and regulatory means, use of pesticides to control psyllid vectors in the citrus crop, and biological control of psyllid vectors in non-crop reservoirs. Citrus greening disease is not under completely successful management.

Greasy spot 

Greasy spot, a fungal disease caused by the Mycosphaerella citri, produces leaf spots and premature defoliation, thus reducing the tree's vigour and yield. Ascospores of M. citri are generated in pseudothecia in decomposing fallen leaves.  Once mature, ascospores are ejected and subsequently dispersed by air currents.

Production 

Brazil is the world's leading orange producer, with an output of 36 million tons (2013), similar in total to the next three countries combined (the United States, China and India). Orange groves are located mainly in the state of São Paulo, in the southeastern region of Brazil, and account for approximately 80% of the national production. As almost 99% of the fruit is processed for export, 53% of total global frozen concentrated orange juice production comes from this area and the western part of the state of Minas Gerais. In Brazil, the four predominant orange varieties used for obtaining juice are Hamlin, Pera Rio, Natal, and Valencia.[http://gain.fas.usda.gov/Recent%20GAIN%20Publications/Citrus%20Semi-annual_Sao%20Paulo%20ATO_Brazil_17-6-2010.pdf GAIN Report Number: BR10005], USDA Foreign Agricultural Service (6/15/2010)

With approximately 16 million tons produced in 2013, the United States is the second largest producer. Groves are located especially in Florida, California, Texas, and Arizona. The majority of California's crop is sold as fresh fruit, whereas Florida's oranges are destined to juice products. Mid-south Florida produces about half as many oranges as Brazil, but the bulk of its orange juice is not exported. The Indian River area of Florida is known for the high quality of its juice, which often is sold fresh in the United States and frequently blended with juice produced in other regions because Indian River trees yield very sweet oranges, but in relatively small quantities. 

Production of orange juice between the São Paulo and mid-south Florida areas makes up roughly 85% of the world market. Brazil exports 99% of its production, while 90% of Florida's production is consumed in the United States.

Orange juice is traded internationally in the form of frozen, concentrated orange juice to reduce the volume used so that storage and transportation costs are lower.

Other countries with significant production of oranges are China, India, Mexico, Spain and Egypt (table).

Juice and other products 

Oranges, whose flavor may vary from sweet to sour, are commonly peeled and eaten fresh or squeezed for juice. The thick bitter rind is usually discarded, but can be processed into animal feed by desiccation, using pressure and heat. It also is used in certain recipes as a food flavoring or garnish. The outermost layer of the rind can be thinly grated with a zester to produce orange zest. Zest is popular in cooking because it contains oils and has a strong flavor similar to that of the orange pulp. The white part of the rind, including the pith, is a source of pectin and has nearly the same amount of vitamin C as the flesh and other nutrients.

Although not as juicy or tasty as the flesh, orange peel is edible and has significant contents of vitamin C, dietary fiber, total polyphenols, carotenoids, limonene and dietary minerals, such as potassium and magnesium. 

Products made from oranges 

* Orange juice is obtained by squeezing the fruit on a special tool (a juicer or squeezer) and collecting the juice in a tray underneath. This can be made at home or, on a much larger scale, industrially. Brazil is the largest producer of orange juice in the world, followed by the United States, where it is one of the commodities traded on the New York Board of Trade.
* Frozen orange juice concentrate is made from freshly squeezed and filtered orange juice. 
* Sweet orange oil is a by-product of the juice industry produced by pressing the peel. It is used for flavoring food and drinks and also in the perfume industry and aromatherapy for its fragrance. Sweet orange oil consists of approximately 90% D-limonene, a solvent used in various household chemicals, such as wood conditioners for furniture and—along with other citrus oils—detergents and hand cleansers. It is an efficient cleaning agent with a pleasant smell, promoted for being environmentally friendly and therefore, preferable to petrochemicals. D-limonene is, however, classified from slightly toxic to humans,  to very toxic to marine life in different countries. 

Limonene is considered a natural chemopreventive agent in humans,   and there is no evidence for its carcinogenicity or genotoxicity, as once believed. The Carcinogenic Potency Project estimates that D-limonene may affect human cancer on a level roughly equivalent to that for caffeic acid via dietary coffee intake,  whereas the International Agency for Research on Cancer (IARC) classifies it under Class 3, which means it is not classifiable as to its carcinogenicity to humans.
* Marmalade usually is made with Seville oranges. All parts of the fruit are used: the pith and pips (separated and placed in a muslin bag) are boiled in a mixture of juice, slivered peel, sliced-up flesh, sugar, and water to extract their pectin, which helps the conserve to set.
* Orange peel is used by gardeners as a slug repellent.
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