The first citrus fruits may have come from southern China

Citrus fruits’ hometown is in China, a genetic analysis suggests.  

An extensive look at wild members of the orange family tree hints that the first species in the Citrus genus arose around 8 million years ago in what’s now south central China, researchers report October 2 in Nature Genetics. The Citrus lineage’s ancestors may have first arrived in Asia on the Indian tectonic plate around 25 million years ago, when it collided with the Asian plate.

Today, myriad tart fruits — including human-bred versions of oranges, lemons and limes — stockpile grocery store shelves. But it’s unclear where their oldest ancestors evolved. Previous studies pointed to places like northeastern Australia, southern China or the southeastern foothills of the Himalayas. Piecing together citrus evolution could help researchers make drought- or disease-resilient plant varieties that still bear tasty fruit, says horticulturalist Qiang Xu (SN: 4/14/15).

To pinpoint Citrus’ origins, Xu, of Huazhong Agricultural University in Wuhan, China and colleagues built a family tree using the genetic blueprints of 314 Citrus and Citrus-related plants, which included 15 Citrus species. The researchers also trekked into the field to find where the trees grow in the wild. The oldest citrus fruits — including C. trifoliata, the trifoliate orange — are found in south central China, suggesting that region is the genus’ birthplace.

Citrus evolution didn’t stop there. Some species have roots in the regions that the earlier studies identified, the team found. Pomelo and citron fruits appear to have sprung up in the Himalayan foothills, and some wild limes evolved in Australia.

The researchers also confirmed that a gene called PH4 is linked to the amount of citric acid inside each fruit. PH4 turns on a proton pump that allows citric acid to build up inside oranges and their relatives. The more citric acid, the more tart the taste.