The origins of today’s citrus fruits are reported online this week in Nature, providing a new evolutionary framework for this common group of plants that challenges current taxonomical thinking.
Citrus trees are the most widely cultivated fruit trees in the world, but the origins and history of Citrus have been unclear. In this study, Guohong Albert Wu and colleagues analysed the genomes of 60 different citrus varieties, including 30 that are newly sequenced, from the Australian finger lime to the Cleopatra mandarin. Today’s citrus trees are descended from at least ten natural citrus species, they report. Citrus diversified during the late Miocene epoch, 6 to 8 million years ago, and spread rapidly through southeast Asia - a transition that correlates with the weakening of the Asian summer monsoons. Australian citrus fruits diversified more recently, around 4 million years ago, when they crossed the Wallace Line, a transitional zone between Asia and Australia.
The authors also studied the domestication of commercial citrus fruits from their wild ancestors, and they show that genes from the pummelo, a natural citrus fruit that resembles a large grapefruit, may have contributed to the mandarins.