watermelon was domesticated in Sudan from Kordofan melon, new genetic study suggests | Genetic

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Scientists have sequenced and analyzed the genome of the Kordofan melon (Citrullus lanatus subsp. cordophane), a Sudanese form of melon with a whitish non-bitter pulp, and found the subspecies to be the closest relative of domesticated watermelons (Citrullus lanatus subsp. vulgaris) and a possible ancestor.

A melon from Cordofan (Citrullus lanatus subsp. cordophane) from North Darfur, Sudan. Image credit: Renner et al., doi: 10.1073 / pnas.2101486118.

Domesticated watermelon is among the 10 most important crops in Central Asia, and knowing its geographic origin and potential parent would help targeted breeding efforts.

The geographical region of its domestication has long remained unclear with competing hypotheses favoring southern Africa, West Africa and North-East Africa, in particular the region of Kordofan, a former province of Sudan bordering the North and South Darfur, and part of the western Sahelian savannas.

outraged Citrullus lanatus, genre Citrullus contains six other species, four of which (Citrullus amarus, C. ecirrhosus, C. naudinianus, and C. rehmii) are from the Namib-Kalahari region, a (Citrullus mucosospermus) in West Africa (Benin, Ghana and Nigeria), and one (Citrullus colocynthis) in North Africa to western India.

All wild species have a white pulp that cannot be eaten raw due to the presence of bitter terpene compounds. Only the fruits of Citrullus mucosospermus are sometimes not bitter but rather bland; the large, soft seeds of this species are used in West African ‘egusi’ stews.

“Based on DNA, we found that watermelons as we know them today – with a sweet, often red pulp that can be eaten raw – were genetically the closest to the wild African forms of Africa. ‘West and Northeast Africa,’ said Professor Susanne Renner, researcher at the Institute for Systematic Botany and Mycology at the University of Munich and the University of Washington.

Professor Renner and his colleagues have found that a Sudanese form with a non-bitter whitish pulp, the Kordofan melon, is the closest relative of domesticated watermelons.

The results are consistent with newly interpreted Egyptian tomb paintings which suggest that watermelon may have been eaten in the Nile Valley for dessert around 4,200 years ago.

“It was the paintings from Egyptian tombs that convinced me that the Egyptians ate cold watermelon pulp,” Professor Renner said.

“Otherwise, why place these huge fruits on flat platters next to grapes and other sweet fruits?”

Kamara papyrus illustrating a Citrullus fruit (red circle), interpreted as a wild watermelon;  the striped and globular fruit recalls the morphology of the Kordofan melon.  Image credit: Renner et al., Doi: 10.1073 / pnas.2101486118.

Kamara papyrus depicting a Citrullus fruit (red circle), interpreted as a wild watermelon; the striped and globular fruit recalls the morphology of the Kordofan melon. Image credit: Renner et al., doi: 10.1073 / pnas.2101486118.

The study also corrects an old taxonomic error that grouped watermelons into the same category as Citrullus amarus, also known as the South African melon.

“Today’s watermelon comes from a very small genetic stock and is very susceptible to disease and insect pests, including various downy mildew, other fungi, viruses and nematodes,” Professor Renner said.

“So far we have found variation in three disease resistance genes between Kordofan melon and domesticated watermelon. Breeders could use this and other information from the genome. “

“Watermelon is one of the most important tropical fruits, with over 200 million tonnes produced each year, but it is also very susceptible to disease,” said Dr Guillaume Chomicki, researcher at the Department of Animal and Plant Sciences of the University. of Sheffield.

“There are specific diseases of watermelon, such as the watermelon mosaic virus, and they are also very susceptible to fungal infections. In conventional agriculture, they are frequently treated with fungicides and insecticides to limit virus transfer.

“Our analysis clearly shows that the Kordofan melon has more disease resistant genes, and different versions of those as well.”

“This means that the Kordofan melon genome has the potential to help us produce disease-resistant watermelons and enable the editing of non-GM genes. Achieving this would significantly reduce the use of pesticides in the cultivation of watermelon. “

The results were published in the Proceedings of the National Academy of Sciences.

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Susanne S. Renner et al. 2021. A genome at the chromosomal level of a Kordofan melon sheds light on the origin of domesticated watermelons. PNAS 118 (23): e2101486118; doi: 10.1073 / pnas.2101486118


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