Apple

• 1. Introduction

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  An apple seed almost never grows into the apple you planted. Sow a seed from a sweet, crisp fruit and the tree that rises will bear something strange, often small and bitter, unlike either parent. Growers call seedling apples "extreme heterozygotes": each one different from every other and from the fruit it came from. That single biological fact shapes everything about how apples reached your kitchen. To keep a good apple, you cannot keep its seeds. You must clone it. So how did a wild fruit from the mountains of Central Asia become more than 7,500 named varieties grown around the world? Why does the same genus that gives us the orchard apple also carry a poison in its pips, a place in Norse and Greek myth, and a starring role in the story of Adam and Eve? And why did one tart, bitter ancestor named Malus sieversii survive on the western slopes of a single mountain range while its eastern cousins left no mark at all?

• 2. Roots In The Tian Shan

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  On the forested flanks of the Tian Shan mountains, the wild ancestor of the cultivated apple still grows. That ancestor is Malus sieversii, found in southern Kazakhstan, Kyrgyzstan, Tajikistan, and northwestern China. Central Asia is generally treated as the apple's center of origin because the wild specimens there hold so much genetic variability. The domestication likely began somewhere between 4,000 and 10,000 years ago in those mountains. From there the fruit travelled the Silk Road toward Europe. Along the way it crossed with wild crabapples: M. baccata from Siberia, M. orientalis from the Caucasus, and M. sylvestris from Europe. That exchange ran so deep that many apple populations ended up more closely related to crabapples than to their morphologically similar progenitor. Only the M. sieversii trees on the western side of the Tian Shan contributed genetically to the domesticated apple. The isolated population on the eastern side left nothing behind. Genetic detective work later confirmed the lineage. Re-sequencing of multiple accessions pointed to Malus sieversii as the wild ancestor, while also revealing extensive introgression from Malus sylvestris after domestication. Unusually for a domesticated fruit, the wild ancestor is only slightly smaller than the modern apple. The earliest physical traces are older still. At the Sammardenchia-Cueis site near Udine in Northeastern Italy, seeds from some form of apple were found in material carbon dated to between 6570 and 5684 BCE. Whether those ancient seeds were wild M. sylvestris or already carried M. sieversii ancestry, genetic analysis has not yet been able to say.

• 3. The Art Of Grafting

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  Grafting was certainly known in European classical antiquity, when there was already substantial apple production. It is the answer to the problem of seeds that refuse to breed true. To keep the best cultivars, growers join a cutting onto a rootstock, cloning the parent rather than gambling on its offspring. Dwarf rootstocks can be traced as far back as 300 BCE, to the area of Persia and Asia Minor. Alexander the Great sent samples of dwarf apple trees to Aristotle's Lyceum. Dwarf rootstocks became common by the 15th century, then passed through several cycles of popularity and decline around the world. The rootstock does far more than shrink a tree. It can change winter hardiness, insect and disease resistance, and soil preference, and it sets the pace of growth and the eventual size of the tree. Dwarf rootstocks produce trees less than 10 ft high at maturity that bear fruit years earlier than full-size trees and are easier to harvest. Most of the rootstocks used to control size were developed in England in the early 1900s. The East Malling Research Station ran extensive research, and its rootstocks carry an "M" prefix to mark their origin. Those crossed later with the cultivar 'Northern Spy' in Merton, England, carry an "MM" prefix instead. New cultivars usually begin as seedlings, arising by chance or bred by crossing promising parents. The words "seedling", "pippin", and "kernel" in a variety's name hint that it began that way. Apples can also throw bud sports, mutations on a single branch, some of which become improved strains or entirely new cultivars.

• 4. Anatomy Of The Pome

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  The fruit is a pome that matures in late summer or autumn. Its true fruits, the carpels, are the harder interior chambers inside the core. There are usually five carpels, though there may be as few as three, and each chamber holds one or two seeds. The edible flesh is not the fruit at all in the strict sense. It forms from the receptacle at the base of the flower, while the five sepals stay attached and stand out from the apple's surface. The blossoms that begin all this appear in spring, opening at the same time as the leaves on spurs and some long shoots. When a flower bud first cracks open its petals are rose-pink, fading to white or light pink when fully open, each flower 3 to 4 cm across. The five-petaled flowers gather in a cyme of 3 to 7 blooms. The central one is called the "king bloom"; it opens first and can grow a larger fruit. The whole arrangement is fragile to cold. Open blossoms are damaged by even brief exposure to temperatures of -2 C or lower, although the overwintering wood and buds endure down to -40 C. The ripe fruit comes in a wide palette. Its groundcolor runs yellow, green, yellow-green, or whitish yellow, while the overcolor can be orange-red, pink-red, red, purple-red, or brown-red, covering anywhere from 0 to 100 percent of the skin. That skin may be wholly or partly russeted, rough and brown, and it always wears a protective layer of epicuticular wax. The scent and flavor come from a long roster of volatile compounds, among them acetaldehyde, ethyl acetate, hexanal, and ethyl butyrate.

• 5. Pollination And Harvest

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  Apples are self-incompatible, which means a tree cannot fertilize itself and must cross-pollinate to set fruit. Each flowering season, growers bring in pollinators to carry pollen between trees. Honey bees do most of the work. Orchard mason bees serve as supplemental pollinators in commercial orchards, and bumblebee queens turn up but rarely in numbers large enough to matter. Timing is everything in this system. Cultivars are sometimes classified by the day of peak bloom within the average 30-day blossom period, and pollinizers are chosen from cultivars that overlap within a 6-day window. There are four to seven pollination groups depending on climate. Group A flowers early, from 1 to the 3rd of May in England, and includes 'Gravenstein' and 'Red Astrachan'. Mid-season Group C, from 8 to the 11th of May, holds 'Granny Smith' and 'Cox's Orange Pippin'. The latest, Group H from 24 to the 28th of May, includes 'Court-Pendu Gris'. A cultivar can be pollinated by one from its own group or a close neighbor, A with A or A with B, but not A with C or D. The harvest that follows depends on the cultivar and the rootstock beneath it. Mature trees typically bear 40 to 200 kg of apples each year, though a poor year can drop yield close to zero. Trees grafted on dwarfing rootstocks bear about 10 to 80 kg. Pickers climb three-point ladders built to fit among the branches. Ripening times scatter across the calendar. Summer producers include 'Sweet Bough' and 'Duchess', fall brings 'Blenheim', and winter producers include 'King', 'Swayzie', and 'Tolman Sweet'.

• 6. Keeping The Crop

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  Pliny the Elder, writing in the 1st century, laid out how to store apples. He said to place them in a room with good air circulation from a north-facing window, on a bed of straw, chaff, or mats, keeping windfalls separate. Such methods stretch the shelf life of fresh apples, but even sturdy winter varieties keep only until December in cool climates. Medieval Europeans took a different path for the long haul. They strung up cored and peeled apples to dry, whole or sliced into rings. Until the 20th century, farmers stored apples in frostproof cellars through the winter for their own use or for sale. The real breakthrough came from a laboratory. Controlled atmosphere facilities use high humidity, low oxygen, and managed carbon dioxide levels to hold fruit fresh year-round. They were first researched at Cambridge University in the 1920s and first used in the United States in the 1950s. Lowering the oxygen slows respiration, which slows softening once the fruit is already fully ripe. There is a hormone working against the storekeeper. The gas ethylene drives ripening, so for storage longer than about six months apples are picked earlier, before full ripeness, when their ethylene output is low. In many varieties that early picking raises sensitivity to carbon dioxide, which then also has to be controlled. Some varieties simply last longer; 'Granny Smith' and 'Fuji' keep more than three times as long as others. Non-organic apples may be sprayed with 1-methylcyclopropene, which blocks the fruit's ethylene receptors and temporarily holds off ripening.

• 7. Naming The Apple

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  The apple as a species carries more than 100 alternative scientific names. Two dominate modern use: Malus pumila and Malus domestica. M. pumila is the older name, but M. domestica became far more common starting in the 21st century, especially in the western world. The shift was not quiet. A proposal to conserve M. domestica was voted down by the Committee for Vascular Plants of the IAPT in 2014. In April 2017 the same committee reversed course by a narrow majority, and in June 2017 the General Committee of the IAPT approved the change, officially conserving M. domestica. Even so, some works published after 2017 still treat M. pumila as correct under an alternate taxonomy. The roots of the dispute reach back centuries. When Linnaeus first classified the group in 1753, he folded pears, apples, and quinces into one genus he called Pyrus, naming the apple Pyrus malus. The botanist Philip Miller split the apple off from Pyrus in The Gardeners Dictionary in 1754, though he did not clearly state that by Malus pumila he meant the domesticated apple. The earliest use of var. domestica for the apple came from Georg Adolf Suckow in 1786. The fruit's English name has its own tangled past. The word apple comes from Old English aeppel, meaning "fruit" rather than the apple specifically, which descends through Proto-Germanic aplaz from Proto-Indo-European h2ebol. As late as the 17th century the word meant any fruit, even nuts. A 14th-century Middle English phrase, appel of paradis, meant a banana.

• 8. The Fruit Of Myth

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  Eleven golden apples were offered to woo the beautiful Gerdr. In Norse mythology, Skirnir, acting as messenger for the Vanir god Freyr, made that offer in stanzas 19 and 20 of Skirnismal. The goddess Idunn carries the same theme further. In the Prose Edda, written in the 13th century by Snorri Sturluson, she provides the gods apples that grant eternal youthfulness. The scholar H. R. Ellis Davidson tied these stories to real practice, noting that buckets of apples were found in the Oseberg ship burial in Norway, and that fruits and nuts appear in early Germanic graves. She found apples bound up with fertility again in the Volsunga saga, where the goddess Frigg sends King Rerir an apple; his wife eats it, and after a six-year pregnancy bears the hero Volsung by Caesarean section. Davidson even pointed to the "strange" phrase "Apples of Hel" in an 11th-century poem by the skald Thorbiorn Brunarson, suggesting the apple was thought of as food of the dead. Greek myth gave the apple a sharper edge as a symbol of discord. Excluded from the wedding of Peleus and Thetis, the goddess Eris threw in a golden apple inscribed Kalliste, "For the most beautiful one". Hera, Athena, and Aphrodite all claimed it. Paris of Troy, bribed with the promise of Helen of Sparta, awarded it to Aphrodite and so indirectly caused the Trojan War. To the Greeks, throwing an apple was a declaration of love and catching it was acceptance, a custom captured in an epigram claiming authorship by Plato. The same fruit threads through other traditions. In Celtic myth the otherworld bore names like Emain Ablach, "Emain of the Apple-trees", echoed in Avalon of Arthurian legend. In China, apples symbolize peace because the first sound of the word for apple, "ping", is homophonous with the word for peace. And in Christian tradition the unnamed forbidden fruit of Eden became an apple through wordplay between the Latin malum for apple and malum for evil, leaving its trace in the name "Adam's apple" for the human larynx.