title: Cytogenetic relationships among Citrullus species in comparison with some genera of the tribe Benincaseae (Cucurbitaceae) as inferred from rDNA distribution patterns.
abstract: BACKGROUND
  Comparative mapping of 5S and 45S rDNA by fluorescent in situ hybridization (FISH) technique is an excellent tool to determine cytogenetic relationships among closely related species.
  
  
  RESULTS
  In this study, the number and position of 5S and 45S rDNA loci in all Citrullus species and subspecies were determined. The cultivated watermelon (C. lanatus subsp. vulgaris), C. lanatus subsp. mucosospermus, C. colocynthis and C. naudinianus (or Acanthosicyos naudinianus) had two 45S rDNA loci and one 5S rDNA locus which was located syntenic to one of the 45S rDNA loci. C. ecirrhosus and C. lanatus subsp. lanatus had one 45S rDNA locus and two 5S rDNA loci, each located on a different chromosome. C. rehmii had one 5S and one 45S rDNA locus positioned on different chromosomes. The distribution of 5S and 45S rDNA in several species belonging to other genera in Benincaseae tribe was also investigated. The distribution pattern of rDNAs showed a great difference among these species.
  
  
  CONCLUSIONS
  The present study confirmed evolutionary closeness among cultivated watermelon (C. lanatus subsp. vulgaris), C. lanatus subsp. mucosospermus and C. colocynthis. Our result also supported that C. lanatus subsp. lanatus was not a wild form of the cultivated watermelon instead was a separate crop species. In addition, present cytogenetic analysis suggested that A. naudinianus was more closely related to Cucumis than to Citrullus or Acanthosicyos, but with a unique position and may be a link bridge between the Citrullus and the Cucumis.
authors.affiliation: Institute of Integrative Plant Biology, School of Life Sciences, Jiangsu Normal University, Xuzhou, 221116, China.
authors.forename: Kun-Peng
authors.initials: KP
authors.lastname: Li
authors.affiliation: Institute of Integrative Plant Biology, School of Life Sciences, Jiangsu Normal University, Xuzhou, 221116, China.
authors.forename: Yun-Xiang
authors.initials: YX
authors.lastname: Wu
authors.affiliation: National Engineering Research Center for Vegetables, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing, 100097, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Institute of Integrative Plant Biology, School of Life Sciences, Jiangsu Normal University, Xuzhou, 221116, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Institute of Integrative Plant Biology, School of Life Sciences, Jiangsu Normal University, Xuzhou, 221116, China.
authors.forename: Xing-Ming
authors.initials: XM
authors.lastname: Lü
authors.affiliation: Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences, Zhengzhou, 450009, China.
authors.forename: Ji-Ming
authors.initials: JM
authors.lastname: Wang
authors.affiliation: National Engineering Research Center for Vegetables, Beijing Academy of Agriculture and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing, 100097, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Institute of Integrative Plant Biology, School of Life Sciences, Jiangsu Normal University, Xuzhou, 221116, China. zongyunli@jsnu.edu.cn.
authors.forename: Zong-Yun
authors.initials: ZY
authors.lastname: Li
authors.affiliation: Institute of Integrative Plant Biology, School of Life Sciences, Jiangsu Normal University, Xuzhou, 221116, China. hanyonghua@jsnu.edu.cn.
authors.forename: Yong-Hua
authors.initials: YH
authors.lastname: Han
mesh_terms: D029773:Citrullus / Q000166:cytology* / Q000235:genetics; D019662:Cucurbitaceae / Q000166:cytology / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics*; D056426:Genetic Loci; D017404:In Situ Hybridization, Fluorescence; D013045:Species Specificity; D026801:Synteny
chemical_list: D018744:DNA, Plant; D004275:DNA, Ribosomal
keywords: Citrullus species; Cytogenetic relationship; Fluorescence in situ hybridization; Oligonucleotides probes; rDNA