New DNA evidence has shown that all citrus fruits can trace their roots to the southeast foothills of the Himalayas some eight million years ago. 

A study, now published in Nature journal, carried out by numerous international scientists analyzed the genomes of dozens of varieties of citrus fruit.

"On the basis of genomic, phylogenetic and biogeographic analyses of 60 diverse citrus and related accessions, we propose that the centre of origin of citrus species was the southeast foothills of the Himalayas, in a region that includes the eastern area of Assam, northern Myanmar and western Yunnan," the scientists said.

They believe that when the climate changed millions of years ago, bringing weaker monsoons and drier weather, the plants were able to spread out of the Himalayas, and throughout southeast Asia.

From there, they spread to the rest of the world about four million years ago.

"By distinguishing between pure species, hybrids and admixtures, we could trace the genealogy and genetic origin of the major citrus commercial cultivars," they said.

"Both the extensive relatedness network among mandarins and sweet orange, and the association of pummelo admixture with desirable fruit traits suggest a complex domestication process."

Genetic maps of the different citrus varieties found today may help scientists find out which fruits can withstand pests, and perhaps develop new citrus fruits.

"Understanding the species diversity and genetic relatedness is the first step towards breeding new varieties of citrus fruits, both with desirable flavor and disease-resistance," lead researcher Guohong Albert Wu of the US Department of Energy Joint Genome Institute was quoted as saying by the BBC.

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