Gene Sequences Present in Citrullus sp. and having been Lost during Domestication of Watermelon

As a result of many years of domestication and selection for desirable fruit qualities, watermelon heirloom cultivars (Citrullus lanatus var. lanatus) share a narrow genetic base and are susceptible to a large number of diseases and pests. On the other hand, a wide genetic diversity exists among Citrullus species collected in Africa, the center of origin of this genus. The recent international watermelon genome sequencing project revealed genomic regions that were preferentially selected, while a considerable number of gene sequences, among them several disease-resistance genes, were lost during domestication. To understand the underlying process of watermelon evolution and domestication we designed PCR primers for the "lost" gene sequences and conducted PCR experiments with genotypes representing the different Citrullus species. Among them C. lanatus var. citroides, C. lanatus var. lanatus, C. colocynthis, C. ecirhosus and C. rehmii. The results in this study elucidate junctures in watermelon evolution and domestication. Also, this study identifies Citrullus genotypes that contain the "lost" genes. These genotypes might be useful in future breeding programs aiming to enhance disease resistance in watermelon.