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Sweeter, more blight-resistant watermelon on the cards

By RJ Whitehead , 27-Nov-2012
Last updated on 27-Nov-2012 at 15:08 GMT

Evidence from a significant study now suggests that watermelon is a vital species for genetic research on account of its small genome size, and its diverse genetic mutants and variants. The findings also pave the way for research into genetic improvement of watermelon and other plants.

An international team led by Beijing Academy of Agriculture and Forestry Sciences (BGI) and other institutes has completed the genomic sequencing of watermelon (Citrullus lanatus) and the resequencing of 20 watermelon accessions.

Watermelon is an important cucurbit crop and one of the most important fruits that contributes to food and economic security in addition to human nutrition. It is favoured for being sweet, low-calorie, high in fibre and nutrient-rich.

The availability of a reference genome for a crop is extremely important in the deeper understanding of its molecular breeding and evolutionary history. In the watermelon genome study, published in Nature Genetics, researchers presented a high-quality genome sequence of an East-Asia watermelon cultivar 97103 and resequencing of 20 watermelon accessions spanning the genetic diversity of C. lanatus.

Wealth of opportunities

Jianguo Zhang, BGI’s project manager, said: “The high-quality genomic sequence opens a new way for the further studies of watermelon. The data resources could serve as a robust tool for better exploring the mechanisms underlying significant economic traits and regulatory networks and further for breeding improvement. It will also promote the evolutionary research of cucurbit crops and other basic biological studies such as sugar metabolisms.”

China leads the world in production of the fruit. Despite being over 90 percent water, watermelons do contain important nutrients such as vitamins A and C, and lycopene, a compound that gives some fruits and vegetables their red color and appears to reduce the risk of certain types of cancer. Watermelon is also a natural source of citrulline, a non-essential amino acid with various health and athletic performance benefits.

Genome-wide duplication is a common event for angiosperms, and represents an important molecular mechanism that has shaped modern plant karyotypes. To access the origin of modern cucurbit genome structures, researchers analysed the syntenic relationships between watermelon, cucumber, melon and grape. 

Greater resistance

Watermelon crops suffer significant loss from a number of diseases, therefore there is some urgency for for researchers to investigate the molecular basis for better improving the pathogen resistance of this important crop. 

The results in this study showed that many resistance genes were located on chromosomes in clusters, indicating tandem duplications may serve as the evolutionary basis of resistance genes in watermelon genome. Moreover, evidence from the study supported the previous hypothesis that a large portion of disease resistance genes have been lost during watermelon domestication.

The findings could also dramatically accelerate watermelon breeding toward production of a more nutritious, tastier and more resistant fruit.

"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. Decoding the complete genome of the watermelon and resequencing watermelons from different subspecies provided a wealth of information and toolkits to facilitate research and breeding," said Zhangjun Fei, one of the leaders of the project.

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