AsianScientist (Aug. 25, 2017) – Scientists in China and the US have used genetic tools to trace the journey of the original domesticated apple from the Silk Road to the rest of the world. They publish their work in the journal Nature Communications.
Centuries ago, the ancient networks of the Silk Road facilitated a political and economic openness between the nations of Eurasia. But this network also opened pathways for genetic exchange that shaped one of the world’s most popular fruits: the apple. As travelers journeyed east and west along the Silk Road, trading their goods and ideas, they brought with them hitchhiking apple seeds, discarded from the choicest fruit they pulled from wild trees. This early selection would eventually lead to the 7,500 varieties of apple that exist today.
In this study, researchers at the Boyce Thompson Institute (BTI) in the US, in collaboration with scientists from Cornell University and Shandong Agricultural University in China, sequenced and compared the genomes of 117 diverse apple varieties, including M. domestica and 23 wild species from North America, Europe, and East and central Asia.
Using this data, they created a comprehensive map of the apple’s evolutionary history. Previous studies showed that the common apple, Malus domestica, arose from the central Asian wild apple, Malus sieversii, with contributions from crabapples along the Silk Road as it was brought west to Europe.
“We narrowed down the origin of the domesticated apple from a very broad region in central Asia to the Kazakhstan area west of Tian Shan Mountain,” explained Professor Fei Zhangjun from BTI.
In addition to pinpointing the western apple’s origin, the authors discovered that the first domesticated apple had traveled to the east, hybridizing with local wild apples along the way, yielding the ancestors of soft, dessert apples cultivated in China today.
“We pointed out two major evolutionary routes, west and east, along the Silk Road, revealing fruit quality changes in every step along the way,” said Fei.
Although wild M. sieversii grows east of Tian Shan Mountain, in the Xinjiang region of China, the ecotype there was never cultivated, and did not contribute to the eastern domesticated hybrid. Instead, it has remained isolated all these centuries, maintaining a pool of diversity yet untapped by human selection, added Fei.
The authors also found that M. sylvestris has contributed so extensively to the apple’s genome that the modern apple is more similar to the sour crabapple than to its Kazakhstani ancestor, M. sieversii.
“For the ancestral species, M. sieversii, the fruits are generally much larger than other wild apples. They are also soft and have a very plain flavor that people don’t like much,” said Dr. Bai Yang of BTI. “The hybridization between ancient cultivated apples and M. sylvestris, followed by extensive human selection, resulted in apples with higher and well-balanced sugar and organic acid contents. That is how the apple started to become a popular and favored fruit.”
Another reason for the popularity of apples was their size. While the wild ancestors of modern day domesticated fruits were tiny, wild apples were already relatively large by the time they started being domesticated. By comparing the many different apple genomes, the researchers uncovered evidence supporting two different evolutionary steps contributing to apple’s increase in size—one before, and one after domestication.
Finally, the researchers expect that the extensive genomic data from this study will help breeders improve the quality of apples. Fei’s group has identified important genetic markers for disease resistance, shelf-life, taste and size in modern apple species.
“The genomic regions and candidate genes identified in this study will be very useful to breeders, improving the speed and accuracy of ‘marker-assisted selection’ in apples,” said Fei.
The article can be found at: Duan et al. (2017) Genome Re-sequencing Reveals the History of Apple and Supports a Two-stage Model for Fruit Enlargement.
———
Source: Boyce Thompson Institute; Photo: Pexels.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.
