Biodiversity Miscellany

Old Watermelon Seeds

A bitter mystery: Scientists sequence world’s oldest plant genome from 6,000-year-old watermelon seeds: In a new paper published in the journal Molecular Biology and Evolution, scientists from the Royal Botanic Gardens, Kew and partners in the U.K., Germany and the U.S. have decoded the world’s oldest plant genome, using Neolithic-era watermelon seeds collected at an archaeological site in the Sahara Desert in Libya.

The study combined aspects of archaeological groundwork with cutting-edge genomics research to shed new light on the domestication of the watermelon and how our ancestors consumed the popular fruit’s ancient relatives. Surprisingly, evidence suggests the Neolithic Libyans had a taste for the watermelon’s seeds—a local delicacy still consumed today—but avoided the fruit’s bitter-tasting flesh.

It is estimated that more than 200 million tons of the domesticated watermelon (Citrullus lanatus) are produced globally every year, with the crop being among the top 10 most important in Central Asia. The red-fleshed fruit is generally accepted to have originated in Africa, where a close relative (C. lanatus subsp. cordophanus) was most likely first domesticated in the Nile Valley and what is modern-day North Sudan.

But the discovery in the early 1990s of supposed watermelon seeds at the Neolithic site of Uan Muhuggiag in Libya continued to puzzle scientists. Dr. Susanne S. Renner at Washington University in St. Louis, who together with Dr. Guillaume Chomicki at Sheffield University, led the study, said, “Seed morphology, especially of ancient seeds, was simply insufficient to reliably identify which species those Neolithic settlers in Libya were using.”

The scientists were able to solve the mystery when they analyzed the seeds’ genome and recovered long stretches across all chromosomes—possibly the oldest genome ever recorded in such detail from a plant whose age has been verified using radiocarbon dating analyses. They also sequenced the genomes of dozens of watermelon specimens in Kew’s Herbarium collections, some of which were first collected in the early 19th century.

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