We Finally Know Where Oranges and Lemons Come From

[Randy W]

 

We Finally Know Where Oranges and Lemons Come From
In addition to finding where citrus come from, researchers have pinpointed the genetic origins of the fruits’ tart taste

from the Scientific American

 

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“Citrus is fascinating,” says Gayle Volk, a plant physiologist at the U.S. Department of Agriculture, who studies the genetic preservation of citrus and other fruits. “The number of diverse crops produced through hybridization among different citrus species is much higher than that of apples or grapes.”

Trying to pinpoint exactly where this diverse, heavily cultivated group of fruits originated—previously hypothesized as anywhere from the Himalayan foothills to the balmy jungles of northeastern Australia—has soured the topic for many researchers. But a new paper takes an in-depth genetic approach to fleshing out oranges’ origins, along with those of their citrus kin. The study, published last week in Nature Genetics, analyzed the genomes of hundreds of species across the orange subfamily Aurantioideae—and revealed that citrus-related fruits likely originated on the ancient Indian subcontinent before further diversifying their sharp taste in south-central China.

Aurantioideae is a titanic taxonomic group encompassing more than 33 genera of fruit-bearing plants found throughout Asia, Africa and Polynesia. This includes the Citrus genus, whose members (such as oranges, grapefruit, lemons and limes) are cultivated worldwide.

Horticulturist Qiang Xu of Huazhong Agricultural University in China and his colleagues recently set out to map the evolutionary journey of the orange subfamily. They assembled the genomes of 12 species and compared those with 314 existing genetic records for members of Aurantioideae. They then organized this genetic database into a phylogenetic tree, which is akin to an evolutionary family tree. Using this, the researchers could determine how different varieties and groups are related. This in turn provides clues to when and where certain species originated.

The team found that the precursors to citrus plants originated more than 25 million years ago on the Indian subcontinent as it was ramming into continental Asia (creating the Himalayas in the process). As the continents collided, these ancestral citrus plants spread into Asia, as is evident from citruslike plant fossils discovered in southern China. The researchers posit that true Citrus species, such as mandarins and trifoliate oranges, first evolved in south-central China around eight million years ago. They speculate that other early Citrus species, including the pomelo and citron, emerged slightly later in the Himalayan foothills.

Location appears to have been crucial for the success of these early fruits. Xu thinks south-central China provided “a complex situation for citrus.” He speculates that several million years ago drastic local climate change, which transformed the area from relatively dry tropical conditions to a wetter climate dominated by monsoons, provided ideal growing conditions. He thinks the region’s budding citrus diversity exploded when local human populations began cultivating the plants thousands of years ago for things ranging from food to medicine.

 

 

Edited October 17, 2023 by Randy W (see edit history)