Cytogenetic relationships among Citrullus species in comparison with some genera of the tribe Benincaseae (Cucurbitaceae) as inferred from rDNA distribution patterns.

Kun-Peng Li,Yong-Hua Han,Ji-Ming Wang,Zong-Yun Li,Yong Xu,Hong Zhao,Xing-Ming Lü,Yun-Xiang Wu,Yan Wang

doi:10.1186/s12862-016-0656-6

Abstract

BackgroundComparative 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.ResultsIn 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.ConclusionsThe 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.

Highlights

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
C. naudinianus is so different from the other Citrullus species in gross morphology that it is placed in the genus Acanthosicyos (A. naudinianus) by Jeffrey [3]
In order to learn about the rDNA distribution information in more species closely related with Citrullus species, several species belonging to other genera in Benincaseae tribe were analyzed, including Cucumis sativus inbred line 9930 (2n = 2x =14), Cucumis metuliferus (PI 482465, 2n = 2x =24), Lagenaria siceraria (PI 379367, 2n = 2x = 22), Zehneria mariothii (PI 596649, 2n = 2x = 24), Melothria pendula (Grif 16574, 2n = 2x = 24), Benincasa fistulosa (PI 449332, 2n = 2x = 24), Coccinia sessilifolia (PI 596663, 2n = 2x = 24) and Diplocyclos palmatus (PI 618818, 2n = 2x = 24)

Summary

Introduction

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. C. naudinianus is so different from the other Citrullus species in gross morphology that it is placed in the genus Acanthosicyos (A. naudinianus) by Jeffrey [3]. Various analyses have been carried out aiming to establish phylogenetic relationships among different Citrullus species, the conclusions are inconsistent and the progenitor of cultivated watermelon has not yet been determined [5,6,7,8,9,10,11]. C. ecirrhosus has been found to have closer relative relationship with cultivated watermelon based on sequencing analysis of cpDNA regions [17, 18]. Jarret and Newman [9] proposed that C. rehmii might be the ancestral to cultivated watermelon by the analysis of internal transcribed spacer sequence heterogeneity

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Conclusion