"Pears cannot naturally be" breeded by inbreeding "" "Xinjiang pears are actually" mixed-breeds "of Asian pears and western pears" ... Recently, the team of Professor Zhang Shaoling, director of the Pear Engineering and Technology Research Center of the College of Horticulture, Nanjing Agricultural University, published online in the journal Biogene He has written a research paper and described a detailed "family tree" for the large family of pears in the world. The article not only revealed the origin and propagation path of pears, but also discovered the independent domestication events of Asian pears and western pears.


Pears originated in southwestern China

Pear is delicious, but his life experience has been confusing.

"Pears are important fruit trees cultivated worldwide, and their cultivation history can be traced back to more than 3,000 years ago." Professor Zhang Shaoling introduced. The industry generally believes that the pear genus originated in China about 65-55 million years ago. At present, China is the world's largest pear-producing country, with annual output accounting for more than 60% of the world's total.

"China, Japan, and South Korea are mainly based on Asian pears. The fruits are mainly round, with a sweet and crisp taste. They can be eaten after they mature on the tree. The current cultivated species mainly include white pears, sand pears, Qiuzi pears and Xinjiang Pears; while European and American countries are dominated by western pears, and the fruits are mainly gourd-shaped. After harvesting, it usually takes a period of 'post-ripe' like kiwi to be eaten. The taste is soft, sweet and sour, and has a strong aromatic flavor. There is only one, collectively known as the Western Pears. "Zhang Shaoling told reporters from Science and Technology Daily.

These phenotypic differences stem from differences in the genetic variation of germplasm. Various pear strains belong to different species of the genus Pear, which increases the difficulty of identifying the genetic relationship of different pears. But with the development of sequencing technology, pear's life is no longer a mystery.

In 2012, led by the Pear Engineering Technology Research Center of Nanjing Agricultural University, the world ’s largest cultivated area of ​​Dangshan Su pear was used as a sample to complete the world ’s first fine genome mapping of pears. Subsequently, the scientists completed the gene mapping of the European pear "Bartlett pear", which provided convenience for studying the genetic variation and evolution of the pear.

This time, Zhang Shaoling's team collected 113 representative pear germplasm resources from 26 countries, and conducted resequencing and population genetic research, tracing the history of pear reproduction and transformation to millions of years ago, just like Described a complete and detailed "family tree" for the large family of pears. Finally, it was confirmed that the earliest pears originated in southwestern China, spread to Central Asia through the Eurasian continent, and finally reached western Asia and Europe. After independent domestication, they formed the two major populations of Asian pears and western pears.

"Self-incompatibility" maintains the diversity of pears

Every March in Yangchun is the season of "the blossom of thousands of trees and pears". However, what everyone does not know is that from the bright and beautiful pear flowers to the crisp and juicy pear fruit, it is not a matter of course, and people need to "match the bridge".

It is not an easy task to match Ao Jiao's "Pear Flower Goddess". In addition to looking at the suitability and whether the flowering dates match, it is also necessary to "measure the marriage". This "marriage" refers to the pear gene.

Pear is a typical self-incompatibility species. The same variety is usually not normal after pollination. If there is only one pear tree within a few miles, it will be difficult to bear fruit.

In addition to pears, these Rosaceae fruit trees such as apples, plums, and apricots are all self-incompatible. That is to say, different varieties must be pollinated with each other, just like humans are forbidden to marry close relatives for eugenics. Studies have confirmed that about 60% of higher plants in nature exhibit self-incompatibility, most of which are of the gametophytic self-incompatibility type.

After a long evolution, the pear tree evolved self-incompatibility, inhibited self-incompatibility, and promoted the maintenance of pear diversity. However, this reproductive feature makes the pear heterozygosity is very high, there is a wide range of gene exchange and genetic recombination between varieties of resources. Therefore, research on the genetic background and relationship of pears has always been difficult, and there has been no clear understanding of the differentiation and genetic relationship of different species.

The improvement of sweetness is an important direction of artificial domestication

Interestingly, the study also found that over 2,000 years ago, Asian pears and western pears had "married", thus forming a new interspecific hybrid-Xinjiang pear, this cultivar is known as "Korla fragrant pear" "As the representative, its fruit is sweet and delicate, and it is favored by consumers, and it is the main export variety in China.

According to Professor Wu Jun, the first author of the paper, about 6.6-3.3 million years ago, pears differentiated into two large populations of Asian and Western pears. That is to say, before becoming a cultivated species, wild Asian pears and western pears were differentiated, and due to the different domestication directions of Eastern and Western people, a cultivated population with a large difference was formed. The study found that in the selection and domestication intervals of the Asian pear and western pear genomes, there are candidate genes related to important traits such as growth, development, and resistance, such as fruit size, sugar acid, stone cells, and aroma formation. Among them, the genes related to sugar anabolic metabolism are the most, indicating that the sweetness improvement of pear fruit is an important direction of artificial domestication.

According to experts, drawing a genetic map of the pear family not only opens up new ways for revealing the molecular mechanisms of pear self-incompatibility, tree growth and development, fruit development and quality formation, and important functional genes, but also for breeding. High-yield, high-quality new varieties provide a brand new technology support platform.

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