Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/12/2003
Publication Date: 6/6/2005
Citation: Levi, A., Thomas, C.E., Simmons, A.M., Thies, J.A. 2005. Analysis based on rapd and issr markers reveals closer similarities among citrullus and cucumis species than with praecitrullus fistulosus (stocks) pangalo. Genetic Resources and Crop Evolution. 52:463-470. Interpretive Summary: Watermelon and melon are important vegetable crops in the U.S. Florida, California, Texas, Georgia, and Arizona produce most of these crops which are grown in 44 states. Seed companies and growers are very interested in the development of new varieties with high fruit quality and good resistance to diseases and pests. Watermelon and melon belong to the Cucurbitaceae family. This family also includes other important vegetables such as cucumber and squash. Using DNA technology, this study examined the genetic relationships (DNA similarity) among wild types of vegetables collected in different parts of the world. The data indicate wide genetic differences among wild types of cucumber and melon, but less differences among the wild types of watermelon. Therefore, it may be easier to use traditional breeding procedures with wild types that have a close genetic relationship to watermelon or melon. On the other hand, biotechnology procedures might be used to isolate disease and pest resistant genes in wild types that have a distant genetic relationship, and introduce such genes to watermelon or melon. This work shows the possibilities of using the wild cucurbit types to improve watermelon and melon, and this will be useful to seed companies.
Technical Abstract: Phylogenetic relationships were examined among several cucurbit species including Cucumis sativus (cucumber), Cucumis melo (melon), Cucumis africanus, Cucumis metuliferus, Cucumis anguria, Cucumis meiusei, Cucumis myriocarpus, and Cucumis zeyheri. We also examined varieties and PIs of watermelon (Citrullus lanatus var. lanatus), a related subspecies of watermelon (C. lanatus var. citroides), the wild subspecies Citrullus colocynthis, and the wild species Citrullus vulgaris var. fistulusus. The latter is a species that has been reported to be a relative of watermelon. The results indicate a close phylogenetic relationship among the Citrullus lanatus subspecies (55-89% genetic similarity), and wide genetic distance with Citrullus colocynthis (29% genetic similarity between C. lanatus and C. colocynthis). On the other hand, wide genetic distances were found among Cucumis species (14-68% genetic similarity). Wide genetic distances were found among Cucumis sativus, Cucumis anguria, Cucumis meiusei, Cucumis africanus, and Cucumis zeyheri (14-59% genetic similarity). Moreover, wide genetic diversity were found among PIs of Cucumis metuliferus (67-97% genetic similarity); this species has been reported to be resistant to the root knot nematode. Overall, the phylogenetic distances among some Cucumis species found not to be significantly wider than those with the Citrullus spp. (8-20% genetic similarity between Cucumis and Citrullus PIs). However, although Citrullus vulgaris var. fistulosus has been considered a relative of Citrullus spp., it appears to be distinct and equally distant from both Cucumis and Citrullus species; genetic similarities between C. vulgaris var. fistulosus and Cucumis or Citrullus groups were found to be less than 4%. Even though there is wide phylogenetic differences among the cucurbit species examined in this study, it may be possible for researchers and seed companies to use them as a germplasm source to enhance watermelon or melon using conventional breeding or biotechnology procedures.