Discovering the trait “Moon and Start” in watermelon
When I started working as a breeder many, many years ago, I was fortunate to be responsible for a small, recently started watermelon breeding program.
Start an improvement program is like starting with a blank canvas for a painter. Once the objectives of the improvement program are established, which are the markets that it is going to serve, what are the resources that you will have available to execute it, etc …, the next step, and one of the most important, is to search the germplasm from which you are going to start developing the breeding program. The starting germplasm is like the pots of colors that a painter will use to make the color mixtures.
Looking for a source of germplasm, I found diverse information on ancient varieties of watermelon, and one of the varieties that most caught my attention at that time, was what some Internet pages called “Moon and Stars” watermelons. In these watermelons, the skin of the fruit had a large yellow spot, representing the moon, and a multitude of smaller, equally yellow spots that represented a praetor of stars, all on the dark green-black background of the color of the skin.
At first glance it might seem that it was the typical symptomatology of some viral disease, but no, it was not an expression of pathological symptoms, it was a genetic variation that had as phenotypic expression those large yellow spots in one case and of tiny sizes but with a wide distribution in other cases, all on the surface of the same fruit.
Genetic control
The first reference we have about this character dates from 1926, where the first variety with that character was apparently launched. However, it was not until 1986 when the first genetic characterization of this trait was carried out (Rhodes, 1986). In the aforementioned work, on genes that affected the coloration of watermelon foliage, it was established that there was a dominant effect gene for which the name of Sp, spotted, was proposed, which showed the phenotypic expression described, not only in the foliage but also on the surface of the fruits. This was later confirmed in another work carried out in 2006, where the presence of spots could also be verified not only in fruits with dark green-black skin color, but also on plants that showed variegated patterns of skin color.
Recently a new research has been presented (Liu et al., 2021), where it is established that the character “moon and stars” is under the genetic control of two dominant genes that interact, which have been called SP1 and SP2. It has also been verified that the characteristic yellowish spots of the expression of the character are also expressed in leaves and cotyledons. The analysis with molecular markers carried out in the populations under study shows that these genes are located on chromosomes 1 and 8 of the watermelon genome.
Future interest of trait
Except for the websites that sell seeds of traditional varieties such as Seedsarvers o Rareseeds, I do not know of any seed company for professional use that has made any effort to develop a line of varieties with this character. It may be that in the future some watermelon improvement program will pay attention to this genetic variant and launch a line of varieties with the “Moon and Stars” character. A few years ago the company Enza Zaden launched a variety of peppers with an equally exotic character: pepper fruits with red and yellow striped variegations under the name of Enjoya, and in 2016 this product line was awarded the prize for innovation from Fruit Logistica.
“Moon and Stars” varieties in watermelon
Here are some links to websites that sell watermelon seeds with the character “Moon and Stars”:
References
Rhodes, Genes affecting foliage color in watermelon, Journal of Heredity, Volume 77, Issue 2, March 1986, Pages 134–135, Link.
Gabriele Gusmini, Todd C. Wehner, Qualitative Inheritance of Rind Pattern and Flesh Color in Watermelon, Journal of Heredity, Volume 97, Issue 2, March/April 2006, Pages 177–185, Link.
Dongming Liu, Dongling Sun, Jinfang Liang, Junling Dou, Sen Yang, Huayu Zhu, Jianbin Hu, Shouru Sun, Luming Yang, Characterization and bulk segregant analysis of ‘moon and star’ appearance in watermelon, Scientia Horticulturae, Volume 285, 2021, 110140, ISSN 0304-4238, Link.
