Tracing the origins of watermelons

An international team, led by researchers at the University of Munich, combined genomic and archaeological data to shed light on the geographical origin and domestication traits of watermelons. Found in the wild, Kordofan melons are also grown by farmers in Sudan. Their white, non-bitter pulp can be eaten raw, which is rather unique among wild melons. Ancient Egyptians might also have enjoyed eating raw watermelons as a dessert more than 4,000 year ago. According to this hypothesis, the watermelon-looking fruits painted on fruit trays in two Egyptian tombs and a papyrus could be Kordofan melons. 

“Progenitors of crop plants help us understand our cultural history and know the soils, climates, pests or pollinators that crops are adapted to or depended on,” says University of Munich evolutionary biologist Susanne S. Renner.

The researchers sequenced and analysed the DNA of the domesticated watermelon and seven watermelon species originally from different parts of Africa. They showed that the Kordofan melon is the closest relative of the commercial watermelon, followed by a West African species (C. mucosospermus), whose large and soft seeds are used in the West African egusi stew and whose pulp is bitter in about 80% of the fruits.

“The closest wild relative of domesticated watermelon was considered to be a West African watermelon, but numerous evidences suggest it was domesticated in Northeast Africa, implying a missing part of its domestication history. This discovery provides new material for unveiling the comprehensive history of domestication and breeding in watermelon,” says Sanwen Huang of the Chinese Academy of Agricultural Sciences, who was not involved in this study.

By comparing genomes of highly domesticated watermelons and Kordofan melons, the researchers found variations in genes linked to colour, taste and disease resistance. For example, mutations that resulted in red pulp and sweeter flesh occurred during the domestication process. The team also identified three variations in disease-resistance genes, which could be explored further for targeted breeding efforts. 

“The added value of this study is that scientists and breeders can use the genomic data to identify gene conferring resistance to diseases and pests of watermelon, and improve resistance in elite watermelon cultivars,” says Amnon Levi of the Agricultural Research Center, U.S. Department of Agriculture, who was also not involved in the study.

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