Researchers discover that all citrus fruits originated in Asia

Lemon, orange, mandarin, and grapefruit are some of the most marketed fruits in the world and they all belong to the citrus family. However, due to their high level of hybridization during the domestication process, the current taxonomic classification of the Citrus genus remained unclear.

A team of researchers, led by the Genomics Center of the Valencian Institute of Agrarian Research (IVIA) and the US Department of Energy Joint Genome Institute, in Walnut Creek (USA), have studied the genomes of 58 different citrus varieties, thirty of which are new genomic sequences, from the Australian finger lime (Microcitrus australasica) to the mandarin Cleopatra (Citrus reshni).

The study, published in Nature, shows that the current citrus trees descended from ten natural species from an area close to the Himalayas, which is delimited by eastern India, northern Myanmar, and western Yunnan.

The results of the analysis reveal that citrus fruits diversified eight to six million years ago, during the Miocene, and spread rapidly through Southeast Asia, coinciding with a time when the summer monsoons of this region weakened. The study emphasizes that Australian citrus fruit diversified later, four million years ago.

Domestication modified everything
"The first attempts to domesticate these fruits were based on asexual propagation through apomictic seeds (without fertilization) and the deliberate selection of specific traits," stated Manuel Talon, a scientist and lead author of the IVIA research.

This process generated a complex kinship network among the cultivated citrus fruits that was recorded in their genomes. For example, grapefruit genes may have contributed to mandarins. According to the researchers, the study offers a new evolutionary scenario of citrus that points directly to the reformulation of the genus itself and generates clues about the determinants of desirable traits in edible fruits.

"The information generated will allow us to identify the genome fragments that control the characteristics inherited by citrus species grown from wild species," the authors stated.

This knowledge is very valuable for breeders, producers and the general public because it will help them detect the most effective genetic targets against devastating diseases, such as the Huanglongbing, and develop strategies and approaches for the improvement of varieties that are tolerant to climate change and cultivars that are more nutritious and have a better taste.

In fact, the citrus improvement program, which was developed by the Valencian Institute and that allowed unravelling the origin and evolution of these fruits in this study, uses genomic technologies to produce new varieties of clementines and mandarins that adapt to the current demands of sustainability and tolerance to climate change.

Bibliographic reference: Guohong Albert Wu et al. "Genomics and phylogenetic analyzes of Citrus origins and evolution", Nature, February 7, 2018


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