citrus fruits

Rutaceae Fruits, Citrus Fruits Family Rutaceae, genus Citrus, fruit type is a hesperidium

Oranges, lemons, limes, citron, grapefruit, tangerines Many distinct species have been recognized, but molecular (DNA) analysis suggests only three species: C. medica (citron), C. grandis (pummelo), C. reticulata (mandarin) Diversity in citrus fruit varieties has probably occurred through hybridization among these species. Origin of Citrus uncertain, but likely SE Asia Citron may have originated in India, spread prehistorically to near east and China, arrived in Greece by 2500 BP Pummelo and mandarin also probably originated in tropical SE Asia

spread to China by 2500 BP Sweet and sour oranges probably occurred as spontaneous hybrids between mandarin and pummelo (as happened with modern strawberry) Lime origin also SE Asia (?) Origin of lemon unknown, may have occurred as a spontaneous hybrid between lime and citron Grapefruit appeared in 1750 on Barbados as a spontaneous hybrid between mandarin and a sweet orange

Rutaceae Fruits

Citrus fruit type is a hesperidium, a type of berry with a leathery skin formed by combined exocarp and mesocarp, and filled with oil glands. The endocarp of a hesperidium is composed of fluid filled fleshy hairs that fill the ovary cavities. Sweet oranges are the most widely grown citrus worldwide, three groups are recognized: blood oranges, navel, and normal Valencia, the most common orange variety grown in the US is a normal type Navel oranges are seedless, develop parthenocarpically Derived from a mutant that appeared in Brazil in the early 1800s Navel flowers produce a small ovary above the normal ovary, which forms the fruit The second ovary forms the “navel” of the navel orange Because the plant is sterile, propagated by grafting or cuttings

Rutaceae Fruits

Citrus species were brough to N America in 1493 by Columbus Lemon, bitter orange, and citron established on Hispaniola US citrus crop now produced in Arizona, California, Florida, Texas Total US 2008 citrus production 13,000,000 tons (11,800,000 metric tonnes) World Citrus Production 2007 (metric tonnes)

Oranges Lemons & Limes Tangerines & mandarins China 2,865,000 745,100 14,152,000 Brazil 1,827,930 1,060,000 1,271,000 Spain 2,691,400 880,000 2,080,700 Mexico 4,160,000 1,880,000 355,000 Israel 162,000 50,000 160,000 South Africa 1,400,000 220,000 135,000 Iran 2,300,000 615,000 702,000

Rutaceae Fruits, Lemons and Limes

Lemon juice used as flavoring additive for beverages Oils from lemon skin are extracted and used in perfumes, deodorants and cleaning products Origin of limes is unknown but apparently a trihybrid similar to lemon. Present in Near East ca. 900, and introduced to Europe ca. 1100. Cultivation in N & S America ca. 1600 in Spanish and Portuguese colonies Early uses of lime juice included prevention of scurvy, a disease now known to result from dietary vitamin C (ascorbic acid) deficiency that was common in sailors on long voyages without fresh vegetables. Kegs of lime juice were kept on ships after the connection between citrus juice and prevention of scurvy was demonstrated by J. Lind in 1747.

Rutaceae Fruits, Grapefruit Grapefruits originated in the New World as a spontaneous hybrid between a pummelo and a sweet orange ca 1750 on the island of Barbados. A very recently derived “species”. Pummelo, C. maxima, native to SE Asia, Malaysia, cultvated in S. China and Thailand, not very widely cultivated in the US but increasing in popularity. Brought to Barbados in late 1600s by Capt. Shaddock

pummelo or shaddock Grapefruit cultivated in US since 1880 Pink grapefruit appeared as a mutant bud, or sport, in Florida and propagated by grafting. Ruby red grapefruits were developed in Texas in the 1920s

Solanaceae Fruits,Tomatoes, Peppers, Eggplants Although considered vegetables, botanically these are fruits Family Solanaceae also includes potatoes and tobacco Tomatoes, chili peppers, and potatoes all originated in the New World and were introduced to Europe in the 18th and early 19th centuries. Compared to apples and citrus fruits, they are very new developments in the European diet. Tomatoes are now classified in the same genus as the potato, Solanum but some texts still use the older name Lycopersicon. There are nine wild species native to South and Central America (Peru, Ecuador, Mexico). Solanum esculentum var. cesasiforme, the cherry tomato, is thought to be the direct ancestor of all modern cultivated forms. The tomato was first cultivated in Mexico and was a well established crop at the time of the early European explorers. The name derives from Mayan xtomatal Tomatoes were not widely used in Europe until the early 1800s, initially by Italy and Spain, but the English were slow to adopt them.

The family Solanaceae includes some highly poisonous European species, such as nightshade (Atropa belladonna) and henbane (Hyoscyamus niger), due to the presence of tropane alkaloids. The poisonous properties of these plants has been known since ancient Greek and Roman times. In Shakespeare’s plays, Juliet takes a draught of nightshade to induce a deep sleep, and Hamlet’s father is killed by having henbane extract poured into his ear as he slept. The poisonous relatives of the tomato may have delayed the acceptance of tomatoes as edible fruits by Europeans. Consider that modern biological concepts of evolutionary relationships were not dominant. Linneaus published the first edition of Systema Naturae in 1735. Still, concepts of plant relationships based on similarities of flowers and fruits existed, and the similarities of tomatoes to poison plants, probably together with their novelty, kept them from being quickly adopted as food plants.

Solanaceae Fruits,Tomatoes

Solanaceae Fruits,Tomatoes

Tomatoes were even more slow to be adopted by Americans In 1820 Col. Robert G. Johnson demonstrated the edibility of tomatoes by publicly consuming a bushel of the doubtful fruits. Today tomatoes are the most important fruit vegetable crop produced in the US. In 2007 the US produced 11,500,000 metric tonnes of tomatoes worth about $12 billion. Despite the high value of the commercial crop, home grown tomatoes are often preferred by consumers for their flavor. Commercial varieties have been developed for productivity, storage, and shelf life. Large scale commercially harvested tomatoes are picked before they are fully ripe. This prevents the accumulation of sugars and softening of the fruit wall.

Changes in tomato fruits during ripening occur in response to ethylene Ethylene is a volatile plant growth regulator or plant hormones that controls a number of developmental changes in plants. Tomatoes are one of several different fruits that undergo a rapid final burst of ripening (citrus fruits and bananas are other examples) that is accompanied by elevated ethylene production. The ethylene induces various ripening changes including the accumulation of sugars, vitamins, and synthesis of enzymes (pectinases) that soften the fruit wall. Ethylene gas is used to induce ripening of tomatoes and to turn oranges a more uniform color. Genetically modified tomatoes developed in the 1990s had short DNA sequences (coding for antisense RNA) inserted in the genome to interfere with the biosynthetic pathways that produce ethylene and pectinase. The “Flavr Savr” tomato produced by the Biotech company Calgene in 1994 proved not to have the desired characteristics. The FlavrSavr was only produced for a few years.

Fruit Ripening, Ethylene

Solanaceae Fruits

Tomatoes, peppers, eggplants are all berries, simple fruits derived from a single ovary

pericarp

seed

placenta

Cherry tomatoes and wild tomatoes have two carpels, the ripe tomato has two chambers when cut equatorially. Most table tomatoes have multiple carpels and several locules in the mature fruit.

The placenta produces a gelatinous substance that surrounds the seeds

Solanaceae Fruits, Peppers

Like Tomatoes, peppers (Capsicum species) are native to South and Central America and were first domesticated in Mexico. Pepper seeds 7,000 years old have been found at the archaeological site Tehuacán in southern Mexico, although these are not considered cultivated. This site is also the oldest known source of maize. Capsicum was first cultivated in S America at least 4,000 years ago. Five species of capsicum are cultivated, the most common is C. annuum, which includes both sweet and pungent types. Changes in domesticated peppers include fruit size and a shift from outcrossing to self pollination. Peppers were introduced to Europe after the voyages of Columbus and were immediately accepted.

Solanaceae Fruits, Eggplant (Aubergine)

Eggplant (Solanum melongena) originated in India or S China, where it has been cultivated for several thousand years. Introduced to Mediterranean region of Europe ca. 1400s by Arabs. The large purple-black fruits associated with contemproary eggplant fruits are unlike the forms of a few hundred years ago which were smaller, light skinned, and resembled chicken eggs. Eggplants are harvested while immature, so the seeds are not fully developed

Cucurbit Fruits, Squashes, Cucumbers and Melons

Several species in the genera Cucurbita, Cucumis Squashes, species of Cucurbita are native to North America Melons, Cucumis melo are native to Africa Cucumbers, Cucumis sativus, are native to India. Fruits of all Curcurbits are pepos. Flowers have an inferior ovary. Like pome fruits, the fleshy tissue is derived from the perianth and pericarp tissues. Pepos are a type of berry that have a tough outer rind. All cucurbits are annual plants, they must be planted each year from seed. All are also monoecious, the flowers have either male or female structures, not both in the same flower. Separate male and female flowers may occur on the same plant.

Cucurbita species may be some of the most ancient cultivated plants C. pepo (summer squash, pumpkin) was domesticated 10,000-9,000 BP in Central America. C. argyrosperma (winter squash) from southen Mexico ca. 7,000 BP. Squashes may have first been domesticated primarily for edible seeds, later selectively bred for starchy vegetables.


C. pepo Summer squash, zucchini, winter squash, acorn squash pumpkin, spaghetti squash

C. moschata Winter squash, butternut squash, pumpkin C. argyrosperma Winter squash, Hubbard squash, turban squash, pumpkin C. maxima Winter squash, winter marrow, pumkin

Squash species domesticated from Central and South America


C. moschata C. pepo

C. argyrosperma C. pepo

C. maxima

C. pepo

Cucurbit Fruits, Squashes, Cucumbers and Melons Cucumis species, melons, cucumber, originated in Africa India, western Asia Watermelon, Citrullus lanatus, native to Africa, wild forms are collected by hunter-gatherer societies there. Other wild melons, Cucumis melo, (musk melon, cantaloupe) occur in Africa, but earliest domestication is known from China Cucumbers, Cucumis sativus, first domesticated in central or western Asia about 3,000 BP. Reportedly carried on caravan journeys as a source of water. Spread by trade into the Mediterranean region of Europe and were cultivated by ancient Egyptians, Greeks and Romans. Other cucurbits, Luffa fruits (Luffa acutangula) are eaten when they are very young and become very fibrous in age.

Dates Dates are fruits of the date palm, Phoenix dacytlifera (Arecaceae) Dates have been cultivated for at least 4000 years and are in important staple food in North Africa and the Middle East.

Prior to domestication, dates presumably were collected by nomadic people from India to the Mediterranean. Dates are highly nutritious, 60-70% carbohydrate and about 5% protein. They are easily preserved by drying. Major date growing countries are Iraq and Saudi Arabia. The date palm was also introduced to Mexico and California by Spanish in the late 1700s.

Date palms are monocots, do not have secondary xylem (wood). They are also dioecious, separate plants produce male and female flowers, and are wind-pollinated. Early agriculturists learned that fruit set was improved by placing a male inflorescence in a female tree more than 4000 years BP. The fruit of date palms is a drupe, like plums and peaches. A wide variety of types are grown, a diversity of sizes, tastes, and textures like the varieties of apples in western cultures.

Dates

medjool dates khadrawi dates

Figs Figs, genus Ficus, family Moraceae, >800 species, mostly tropical Many species have edible fruit, but only one species, F. carica, cultivated for fruit F. carica grows in warm-temperate regions, in US (CA, OR, TX), Australia, Mexico, Chile, South Africa, Mediterranean countries Native to Mediterranean region, mentioned in Egyptian writing ca. 4700 BP Greek name for fig is sykon, the type of fruit of a fig is called a syconium Syconium is an inflorescence enclosed by receptacle tissue. A multiple fruit, like a raspberry, composed of individual drupelets.

Figs, the Oldest Cultivated Plant?

Figs are one of the earliest cultivated plants, possibly THE FIRST: Oldest figs associated with human settlements date to ca 11,400 BP from the Jordan Valley (Israel), and predate domesticated cereals by about 1,000 years. Carbonized fig fruits were found in a neolithic village named Gigal 1 in the Jordan Valley and other sites contemporaneous with Gigal 1(Kislev et al. 2006, Science 312:1372-1374). How is it known that these fruits were cultivated by humans, not just collected by a hunter-gatherer society? The evidence has to do with the complex pollination biology of fig plants. Pollination of figs is a very complicated story, but is crucial to the evidence that figs have been cultivated for at least 11,400 years.

Fig Pollination Biology

Ficus carica plants are dioecious (some other fig species are monoecious). But not typical dioecious, male and female plants. Female plants produce only female flowers that are the edible fruit Male plants have flowers with both male and female structures and so are sometimes called “hermaphroditic”. The fruits of the hermaphroditic plant are not considered edible and are called “caprifigs”. Capra is latin for goat; caprifigs were Roman goat food. Fig flowers are enclosed almost completely by the receptacle. The syconium is actually the closed inflorescence of the fig that also encloses the fruit after fertilization. So, if figs are diocious plants, and if the flowers are completely enclosed in receptacle tissue, how does pollination, fertilization occur?


Figs are pollinated by very small wasps that lay their eggs inside the female flowers in the syconium. Female wasps enter and emerge from the orifice of the syconium to deposit eggs.

wasp emerging from orifice of a fig syconium

Fig trees produce three seasonal cycles of flowers & fruits. Pollen is produced mainly in the spring flowers. Summer and fall flowers and fruits provide food and shelter for successive wasp generations.

Pollen is only produced by the caprifig, and wasp eggs can only mature in caprifigs. Wasp larvae mature in the seed of the caprifig, making it nonviable Edible fruit is only produced by female plants.


The structure of the female flowers is different in caprifig syconia and female plant syconia. The styles of the pistillate female flowers in caprifigs is about 2 mm long, but in female syconia the styles are about 3 mm long. What a difference a millimeter can make! The female wasp lays her eggs in the hermaphroditic caprifig flowers only (the wasp larvae get nourishment from the fertilized flower). The ovipositor of the female wasp is only 2 mm long. So the female wasp can only insert her eggs into the female flowers inside the syconium of a caprifig, the style of the female edible fig flower is too long. But no matter, mature female wasps that emerge from the caprifig flower carry the pollen to the female plant flowers and in doing so fertilize the female plant flowers and produce fertile seeds. Fig wasp larvae can only mature and emerge from caprifigs, which have male flowers and pollen.

Fig Pollination and Evidence for Human Cultivation

OK, so what do fig sex and wasps have to do with human cultivation of figs? The fossilized fig fruits found at Gigal 1 had been collected and probably dried for storage. The fruits had very few, almost no embryos, i.e. no fertile seeds. Some contemporary fig varieties are parthenocarpic, they produce fruit without fertilization. Parthenocarpic mutants arise spontaneously. Parthenocarpic plants do not produce fertile seeds and therefore must be propagated vegetatively, such as by rooted cuttings. The figs found at the Gigal 1 site were parthenocarpic, and so must have been a mutant that was recognized and cultivated by neolithic humans.

Published by AAAS

M. E. Kislev et al., Science 312, 1372 -1374 (2006)

Fig. 1. Carbonized fig fruit (Ficus carica var

A: orifice of syconium B: Scales surrounding orifice C: Fruit skin D: fruit flesh E: drupelets F: drupelets with no seed

Fig Pollination and Modern Cultivation

Smyrna figs are a popular cultivated fig variety that is not parthenocarpic, and the female flowers must be pollinated by wasps to produce fruits. In the Mediterranean region, both female and caprifig types grow together, but when Europeans tried to grow Smyrna figs in North America, they did not understand the complex pollination system and brought only the female Smyrna plants. Figs were not successfully cultivated in America until caprifig trees (in 1880) and later wasps (1900) were imported. Modern fig varieties Kadota and Mission are parthenocarpic. Like apples, and dates, a large variey of different fig named varieties differing in fruit characteristics exists. There are at least 350 named varieties of figs.

Avocados

Avocado, Persea americana (Lauraceae) Because avocado mesocarp contains as much as 30% oil, they have the highest energy content fruit pulp (2000 - 2800 calories per kilogram). Avocado fruits are drupes, like cherries, olives. But the seed is not protected by a hard endocarp. The natural animal dispersers of avocados are not known. Wild avocados are not known, only cultivated avocados are known. Have been found in archeological sites in Mexico dating to about 9000 BP. Although no wild avocados are known, it is believed that avocados were independently domesticated three times.

Mexican variety, light green, thin smooth skin Guatemalan variety, Hass avocado, dark green, thick warty skin West Indian variety, mainly grown in Florida, 8 - 10% oil

Avocados

Mexican type Guatemalan type West Indian type

Some avocado factoids: Grown in the US since 1893, but increased in popularity after the 1920s when advertisers began to deny rumors of aphrodisiac properties. The name avocado is derived from the Aztec ahuacacahuatl, “testicle tree” which may refer to the supposed stimulant properties of the fruit. Mexico is the world’s largest producer and exporter of avocados in 2007 1,140,000 metric tonnes The US produced 250,000 MT

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citrus fruits