Sweeter and more disease-resistant watermelons just may be on their way, thanks to an international consortium of more than 60 scientists that has just published the genome sequence of watermelon (Citrullus lanatus). Such information could dramatically accelerate breeding to produce more nutritious, tastier and more resistant watermelon.
The watermelon genome sequence was published in the Nov. 25 online version of the journal Nature Genetics.
The researchers, who work in the United States, China and Europe, discovered that a large portion of disease resistance genes were lost in the domestication of watermelon. With the high-quality watermelon sequence now complete, it is hoped that breeders may use the information to recover some of these natural defenses.
The authors reported that the genome of the domesticated watermelon contains 23,440 genes, roughly the same number of genes as in humans.
The group compared the genomes of 20 watermelon varieties and developed a first-generation genetic variation map (HapMap) for watermelon. This information allowed them to identify genomic regions associated with fruit color, taste and size.
"Watermelons are an important cash crop and among the top five most consumed fresh fruits; however, cultivated watermelons have a very narrow genetic base, which presents a major bottleneck to its breeding," said Zhangjun Fei, a scientist at the Boyce Thompson Institute for Plant Research (BTI) on Cornell's campus and one of the project leaders.
Fei worked with BTI scientists, among others, on different aspects of the research: James Giovannoni to generate the gene expression data through RNA-sequencing and Lukas Mueller to provide additional analysis to confirm the quality of the genome assembly.
The genome sequences of the watermelon are publicly available at the Cucurbit Genomics Database, which is created and maintained by Fei's group.
Believed to have originated in Africa, watermelons were cultivated by Egyptians more than 4,000 years ago, where the fruit was a source of water in dry, desert conditions. They are now consumed throughout the world -- with more than 400 varieties in global commercial production.
Despite being more than 90 percent water, watermelons contain such nutrients as vitamins A and C and lycopene, a compound that gives some fruits and vegetables their red color. A diet rich in lycopene appears to reduce the risk of certain types of cancer. Watermelon is also a natural source of citrulline, a nonessential amino acid with various health and athletic performance benefits.