The Divergence of Chromosome Structures and 45S Ribosomal DNA Organization in Inferred by Comparative Molecular Cytogenetic Mapping.

W.J.de Wilde & Duyfjes is an annual and monoecious plant. This species is endemic to Southeast Asia, particularly Vietnam. However, is rarely studied, and no detailed information is available regarding its basic chromosome number, 45S ribosomal DNA (rDNA) status, and divergence among other species. In this study, we characterized the morphological characters and determined and investigated the basic chromosome number and chromosomal distribution of 45S rDNA of using the fluorescent in situ hybridization (FISH) technique. A maximum likelihood tree was constructed by combining the chloroplast and internal transcribed spacer of 45S rDNAs to infer its relationship within . had an oval fruit shape, green fruit peel, and protrusion-like white spots during the immature fruit stage. FISH analysis using 45S rDNA probe showed three pairs of 45S rDNA loci located at the terminal region in , similar to . Meanwhile, two, two, and five pairs of 45S rDNA loci were observed for , , and , respectively. One melon (P90) and cucumber accessions exhibited different chromosomal localizations compared with other members of . The majority of species showed the terminal location of 45S rDNA, but melon P90 and cucumber exhibited terminal-interstitial and all interstitial orientations of 45S rDNA loci. Based on molecular cytogenetics and phylogenetic evidence, is more closely related to cucumber than melon. Therefore, may serve as a potential parental accession for genetic improvement of cucumber through interspecific hybridization.