Genetic Relationships in the Desert Watermelon Citrullus colocynthis As Viewed with High Frequency Oligonucleotide–Targeting Active Gene (HFO–TAG) Markers

United States Plant Introductions (PIs) of Citrullus colocynthis (L.) Schrad. are a viable source for enhancing disease and pest resistance in watermelon cultivars. However, there is a little information about their genetic diversity and relationships to watermelon cultivars. Genetic diversity and relationships were examined among 29 accessions of C. colocynthis (CC) collected in northern Africa, the Middle East, and Asia. Also, among 6 accessions of Citrullus lanatus var. lanatus (Thunb.) Matsum. & Nakai (CLL), 12 accessios of C. lanatus (Thunb.) Matsum. et Nakai subsp. lanatus var. citroides (Bailey) Mansf. ex Greb. (CLC) and a PI classified as the desert perennial C. ecirrhosus Cogn. (CE) (Griffin 16945, collected in southern Africa). Twenty-three high frequency oligonucleotides - targeting active gene (HFO-TAG) primers were used in polymerase chain reaction (PCR) experiments to produce a total of 431 polymorphic fragments that represent coding regions of watermelon genome. The analyses showed closer genetic relationships of CC to CLL than to CLC. The desert perennial CE (Griffin 16945), collected in southern Africa, comprises alleles of CC, CLC and CLL, suggesting that it may evolved from a common Citrullus ancestor. The CC PIs differentiated into five subgroups, concuringwith their geographic distribution in northern Africa, the Middle East, and Asia. Although the existence of reproductive barriers resulting in significant reduced fertility, several of the C. colocynthis PIs, particularly those collected in northern Africa, can be crossed with watermelon cultivars and used in breeding programs aimed to enhance watermelon cultivars for disease or pest resistance.