Researchers Uncover the Watermelon’s Origins

A Sudanese plant called the Kordofan melon is the watermelon’s closest wild relative, according to a new study

Kordofan melon
New genetic research finds that the Kordofan melon (pictured), native to Sudan, is the watermelon's closest wild relative. Shan Wu

The green-striped, red-fleshed watermelon might not look inherently mysterious, but botanists have long puzzled over which wild plant the modern domesticated crop originated from. Now, new research claims to provide an answer in the form of a small Sudanese melon called the Kordofan, reports Isaac Schultz for Gizmodo.

Prior to these new findings, published last week in the journal Proceedings of the National Academy of Sciences, the predominant view was that the watermelon’s evolutionary roots were in South Africa, reports Tara Yarlagadda for Inverse.

But once lead study author Susanne S. Renner and her co-authors started sequencing the DNA of wild plants in the watermelon’s genus—Citrullus—a different picture emerged.

“It turned out there were more species than previously thought, and that plants from South Africa were not genetically close to today’s domesticated watermelon,” Renner, an evolutionary biologist at Washington University in St. Louis, tells Inverse.

In 2015, one of Renner’s graduate students, Guillaume Chomicki, took a closer look at the DNA of the supposed South African ancestor of the watermelon and found the two species were more distantly related than expected. “From there, one thing led to another,” Renner tells Gizmodo.

The thinking that the watermelon’s wild progenitors came from South Africa emerged roughly 150 years ago when a student of the famed taxonomist Carl Linneaus came across a melon in a market near Cape Town and dubbed it Citrullus lanatus. The watermelons grown in the United States were soon subsumed under the same Latin binomial.

“From this moment on, the general idea was that the watermelon came from South Africa,” Chomicki, a botanist at the University of Sheffield in the United Kingdom and co-author of the research, tells Gizmodo.

Instead, the results of this genetic study suggest the origins of the watermelon are in northeast Africa in the Kordofan region of southern Sudan. Kordofan melons measure about six inches across and have white, sweet flesh and a bright, somewhat striped green exterior, reports Veronique Greenwood for the New York Times.

painting found in an Egyptian tomb
A painting found in an Egyptian tomb shows the distinctive stripes of a watermelon-like fruit. Washington University St. Louis / Renner et al. 2021

This finding helps explain a tantalizing bit of artwork found inside a 4,300-year-old Egyptian tomb in Saqqara that depicts a big, oblong, green-striped melon alongside grapes and other sweet fruits, according to the Times. Placing the watermelon’s roots in nearby Sudan helps explain what this melon might have been doing in Egypt.

After discovering the true origin of the watermelon, researchers compared the genes of Kordofan melons to a variety of watermelon specimens, some up to 270 years old, to see what genetic changes occurred during domestication.

Per Inverse, the team found 15,824 differences between the genes of the Kordofan melon and a common modern watermelon varietal known as 97103.

Some of these differences may help us understand and even remedy one of the watermelon’s biggest weaknesses as a crop: its susceptibility to disease.

“There are specific watermelon diseases, such as the Watermelon mosaic virus and they are also very sensitive to fungal infections... They are frequently treated with fungicides, and insecticides,” says Chomicki in a statement. “Our analysis clearly shows that the Kordofan melon has more disease resistant genes, and different versions of those too. This means that the genome of the Kordofan melon has the potential to help us breed disease-resistant watermelons and allow non-GM gene editing. Achieving this would be reducing substantially pesticide use in watermelon farming.”

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