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The Science Behind a Favorite Summertime Treat

Posted by Nancy Vanatta, USDA Agricultural Research Service in Research and Science
Jul 02, 2019
Watermelon granita
Watermelon granita is a popular summer dessert. Photo by Nancy Vanatta

Many people consider watermelon a delicious summer treat — whether in granitas, salads or simply freshly sliced. It’s not surprising that July is National Watermelon Month.

Watermelons, which originated in Africa, have been grown in the North America since the 1600s and are an important U.S. crop. According to the National Agricultural Statistics Service, the United States produced 4,494,000 pounds of watermelon in 2016.

What you might not know is that the watermelon you eat today owes its existence to Charles Andrus, a plant breeder with the Agricultural Research Service (ARS) Vegetable Breeding Laboratory. In 1954, Andrus developed the watermelon variety “Charleston Gray,” which takes its name from the South Carolina city where the lab is located. In fact, the humble “Charleston Gray” is in the lineage of 95 percent of watermelons grown in the world today.

Unfortunately, like many other crops, watermelons are susceptible to a variety of diseases and pests, including anthracnose and aphids.

Over the years, scientists at the ARS U.S. Vegetable Laboratory in Charleston have continued studying watermelons in an effort to develop new varieties that are more resistant to diseases and pests. To that end, ARS has been evaluating the genetic diversity within different kinds of watermelon germplasm. The genome of the domesticated watermelon contains 23,440 genes. Sequencing the genome would make valuable traits, such as disease resistance, available to breeders and ultimately growers for breeding watermelons with enhanced protection against major diseases.

Now 65 years after its debut, the “Charleston Gray” watermelon is back in the spotlight. In a long-term study, a research team led by ARS geneticist Amnon Levi at the U.S. Vegetable Laboratory collaborated with scientists at the Boyce Thompson Institute to unlock the genome of "Charleston Gray."

Employing the most advanced genomic technologies available, the team also genotyped an additional 1,365 watermelon lines from the USDA National Plant Germplasm System. This important work will facilitate the identification of valuable new genes with the potential to confer disease and pest resistance—obstacles to enjoying this favorite summertime treat.

Category/Topic: Research and Science