More than eighty million tons of apples are harvested annually in the world, and the number of varieties of this fruit exceeds seven and a half thousand. Scientists have known for a long time that the mountain forests to the west of the Tien Shan, on the territory of present-day Kazakhstan and Kyrgyzstan, were the birthplace of the cultivated apple tree. Recently, a study has emerged that reveals new details of the history of the apple tree. In particular, the author came to the conclusion that the evolutionary changes that eventually led to the emergence of modern apple trees began in their wild ancestors even before people paid attention to these fruits.
Two years earlier, a team of scientists from China and the United States managed to clarify the history of apple trees, comparing the genomes of 117 varieties of cultivated apple trees and 20 wild apple species. The researchers confirmed that the main ancestor of the domestic apple tree (Malus domestica) was the Sivers apple tree from Kazakhstan. Later, when apple trees spread westward along the Great Silk Road, they interbred with local species: in Siberia - with a berry apple (M. baccata), in the Caucasus - with an oriental apple tree (M. orientalis), in Europe - with a forest apple (M. sylvestris). Approximately 46% of the genome of modern apples is inherited from the Sievers apple tree, and 21% from the forest apple.
The history of the cultural apple tree. Far left - Sivers apple tree, further on top - berry apple tree, in the center - eastern apple tree, below - forest apple tree. These four species were the ancestors of the domestic apple tree, which later produced many different varieties.
In the other direction of distribution of apple trees from Central Asia - to the east, to China, they also crossed with local species, the genetic traces of which are preserved in some Chinese varieties. East Asian apple trees, which are now considered independent species: the plum apple tree (M. prunifolia, known to Russian gardeners as "Chinese") and the Asian apple tree (M. asiatica), probably arose as a result of hybridization between the Sievers apple tree and the Siberian berry apple tree.
An unexpected conclusion in a 2017 study turned out that Kazakhstani Sievers apple trees and representatives of the same species growing very close, only on the other side of the mountains, in Xinjiang, are genetically different from each other. And Xinjiang apple trees did not make any genetic contribution to the home apple tree. But now they are considered as a source of potentially useful genes for new varieties.
The new study was authored by Robert N. Spengler III, head of the paleoethnobotany laboratory at the Max Planck Institute for the Study of Human History. His article on the history of the apple tree has been published in Frontiers in Plant Science, and a significant portion of his book Fruit from the Sands. The Silk Road Origins of the Foods We Eat, which is coming out this summer from California university.
An important factor thanks to which apples became the way we know them, Spengler calls adaptation to endozochoria - the spread of seeds with the help of animals eating the fruits. To attract distributors, the fruits of the plants grow larger, acquire a bright color and a sweet taste. At the same time, in representatives of the Rosaceae family, to which the apple tree belongs, two strategies can be observed. Some plants, such as cherries or raspberries, “rely” on birds. Their fruits are small. Others are guided by the eating of fruits by large animals, "megafauna" (Spengler refers to this category of mammals weighing forty kilograms). Such plants tend to gradually increase in fruit size due to the tasty pulp, while the seeds remain small and easily pass through the intestines of mammals.without losing germination.
The apple tree evolved along the second path. Of course, apples became especially large and sweet already in the process of artificial selection, but their increase began without human participation. Until now, wild apples are eaten with pleasure by bears, deer and other animals. Now their role in the spread of seeds is small, since their number of animals is small, and freedom of movement is limited by the preserved forests, but in the Pleistocene era they played a leading role in the settlement of the apple tree.
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It is assumed that, in addition to the Sievers apple tree, this direction of evolution was characteristic of other species of large-fruited wild apple trees (for example, the forest apple and the Nedzwetsky apple tree, Malus niedzwetzkyana), as well as the wild ancestors of the apricot (Prunus armeniaca), peach (Prunus persica), Tibetan peach () or David's peach (Prunus davidiana) growing in China.
Biologists explain the appearance of some large-fruited trees in other families and other regions of the Earth by the same evolutionary adaptation. Sometimes this strategy becomes dangerous. If the host species disappears, the plant closely adapted to cooperate with it experiences significant difficulties and may also disappear. Some South American trees fell into this trap, whose fruits were eaten by representatives of the Pleistocene megafauna - giant sloths and homphoteria. After their extinction, the trees had a hard time. However, some were lucky again and they “found” a new distributor - a person. For example, wild avocado is now quite rare in the forests of South America, but people grow it in the tropics around the world. But if people didn't love avocados, this species would most likely have disappeared by now. Avocados and other plantswhich developed in the course of joint evolution with now extinct animal species, the biologist Daniel Jansen suggested calling it "evolutionary anachronisms."
Robert Spengler notes that, according to paleobotanical data, in the Holocene epoch, many trees of the Rosaceae family in Eurasia experienced a significant reduction in their range. For example, the wild peach is now on the verge of extinction. Spengler found a correlation between the size of the fetus and the reduction in area. The larger the fruit of a tree, the more its distribution decreased after the Pleistocene (before human intervention). It is logical to assume that earlier the seeds were helped by the now extinct species of mammals. The same trees and shrubs whose seeds the birds spread have not experienced similar problems. Even among wild apple trees, the small-fruited berry apple (M. baccata) grows in the wild over a much larger area than the other three ancestral apple species.
But for apple trees, as well as for some other fruit trees, people became the new distributors. The journey from the wild Sievers apple to the domesticated apple was different from the cereal domestication strategy. On the one hand, more attractive fruits could be obtained by bypassing long-term selection over a number of generations. Wild apples in the Tien Shan are characterized by high plasticity and a wide range of phenotypic traits. There are trees in the wild that bear fruits up to eight centimeters in diameter, some wild apple trees can be sweet and aromatic. People could have simply opted for sweeter, larger fruits. But on the other hand, there was also a serious difficulty. With sexual reproduction, the offspring of apple trees does not retain parental characteristics. If we plant a varietal apple seed, a tree with unpredictable properties will grow from it. The desired characteristics of the variety are preserved only by propagation by grafting. But, admittedly, people learned to graft cuttings pretty quickly. Ancient gardeners already knew this method well.
Spengler notes evidence of the consumption of fruits of different types of apple trees even before the spread of the Sievers apple from Central Asia. The most famous dried apple halves found in the royal tomb at Ur. They date from the end of the fourth millennium BC, and most likely belong to the species M. orientalis. Remains of apples from the beginning of the 1st millennium BC e. archaeologists have found in the Kadesh oasis in the Negev desert. The inhabitants of the ancient Near East dried apples, which was not only necessary for long-term storage, but also helped to improve their tart taste when dried apples were used to prepare a decoction. In Europe, the fruits of the forest apple were eaten.
Finds of apple seeds in human settlements 8 - 1 thousand BC e.
The modern cultural apple arose from trade links between Central Asia and the countries of the Middle East and Europe. During its advance along the Great Silk Road, the Sievers apple tree underwent hybridization with local species. Spengler believes that certain species of apple trees were isolated due to periodic glaciations, this isolation persisted later, when the glaciers retreated, and the apple trees were able to overcome it only with the help of humans.
Author: MAXIM RUSSO
