Cucumber, melon's common ancestor originated in Asia

Washington, July 20 (ANI): Cucumber (Cucumis sativus) and honeydew melon (C. melo) have long been thought to have originated and diversified in Africa. However, wild populations which evolved into melons and cucumbers originated in Asia, suggests new research.

The study appears in the Proceedings of the National Academy of Sciences

Professor Susanne Renner, a botanist at Ludwig Maximilian University of Munich, says: "A molecular genetic analysis has now shown that the wild populations that gave rise to melons and cucumbers originated in Asia.

"In addition, we have found that 25 related species which have never been formally described are found in Asia, Australia and regions around the Indian Ocean."

Future genetic studies on C. sativus and its wild relatives should therefore focus on Asia and Australia.

The new results are important because the garden cucumber is one of the most widely cultivated vegetable crops, and the species is among the few flowering plants whose genomes have been fully sequenced.

Renner said: "Our study would not have been possible without the resources of the Munich herbarium and Botanical Garden. A large fraction of the plants we have been able to sequence was collected in India, Vietnam and Australia during the 19th century, and most were then forgotten in herbaria, that is, collections of dried plant specimens. Many of these come from locations that no longer have natural vegetation, for example, because they were collected at sites that now lie in built-up areas of cities like Hanoi."

"We analyzed specific segments of the genetic material from herbarium specimens of more than 100 Cucumis species. The samples we used had been collected at various locations in Africa, Australia and Asia", reports Patrizia Sebastian, who is the first author on the new study.

Sebastian adds: "It turned out that the closest living wild relative of the cultivated melon is a native of Australia. The two lines diverged about 3 million years ago, and they last shared a common ancestor with their more distant relatives in Asia and Australia about 10 million years ago."

The total number of Cucumis species found in Asia and Australia is now around 25, and they branched off from their African relatives some 12 million years ago.

Nine of the 25 species were identified for the first time in the new study. Renner and her colleagues are preparing formal systematic descriptions of the new species for a specialized journal.

Taken together, the results argue that the common ancestor of cucumber and melon originated on the continent of Asia. Possible ancestral populations from which the domesticated forms derive have been localized in the Himalayas. The genetic diversity of the varieties of C. melo that occur in India and China is particularly striking.

Renner says: "Our data also prove that the closest living relative of our garden cucumber is the species C. hystrix, which is found in the Eastern Himalayas. Future investigations of the phylogeny of Cucumis should therefore focus on Asia and Australia." (ANI)