ARS | Publication request: Wild Forms of Watermelon and Genomic Resources

Submitted to: Genetic Resources and Crop Evolution
Publication Type: Book / Chapter
Publication Acceptance Date: June 20, 2010
Publication Date: N/A

Technical Abstract: In this chapter, we reviewed the characteristics, phylogenetic information of all the species in Citrullus genera, including Citrullus lanatus var. lanatus (Thunb.) Matsum and Nakai., C. lanatus var. citrides (Bailey; Mansf.), C. ecirrhosus Cogn., C. rehmii De Winter., C. colocynthis (L.) Schrad, and Acanthosicycos naudinianus (Sond.) C. Jeffrey. We also reviewed the genomic information produced for watermelon, including genetic mapping, DNA markers, and unigenes and their use in introgression of useful traits from wild species to watermelon cultivars. In this manuscript, we also describe our recent study using fluorescence in situ hybridization (FISH) to build cyto-molecular maps and to study karyotype and organization of chromosomes of watermelon cultivars (Citrullus lanatus var. lanatus) versus chromosomes of the wild relative C. lanatus var. citrides. The FISH data show significant differences in the18S-28S rDNA and the 5S rDNA gene copy number, elucidating the wide genetic gape between the two Citrullus lanatus subspecies. Thirty-one accessions of Citrullus spp. belonging to C. lanatus var. lanatus, C. lanatus var. citroids and Citrullus colocynthis were subjected to phylogenetic analysis using combined data sets of AFLPs and SSRs. Tree topologies inferred by Neighbor Joining analysis have resolved the phylogenic relationships among the Citrullus species with special reference to established taxonomic classification. In this study, we have resolved species boundaries of C. lanatus var. citroids, C. lanatus var. lanatus and C. colocynthis into three well-supported clusters. The clustering pattern based on principal coordinate analysis (PCA) with the shared polymorphisms using the subsets of data between any two taxon combinations helped to elucidate the introgression and interrelationships among the Citrullus species. Two groups of C. lanatus var. lanatus were identified. One group is positioned in-between C. lanatus var. lantaus and C. lanatus var. citroides, and a second group is integrated with C. lanatus var. citroids and C. colocynthis.