Reproductive biology and variation of nuclear ribosomal ITS and ETS sequences in the Calligonum mongolicum complex (Polygonaceae).

Wei Shi,Borong Pan,Jun Wen,Yanfeng Zhao,Gabriel Johnson

doi:10.3897/phytokeys.76.10428

Abstract

To explore the biosystematics of the Calligonum mongolicum complex (Polygonaceae), the flowering phenological period, breeding and pollination characters and seed set of the complex (Calligonum Mongolicum Turze, Calligonum chinense A. Los., Calligonum gobicum A. Los., Calligonum pumilum A. Los. and Calligonum zaidamense A. Los.) were documented in the Turpan Eremophyte Botanical Garden, China. The sequences of the nuclear ribosomal ITS and ETS region were employed to differentiate the Calligonum mongolicum complex and other species in sect. Medusae. The results showed species of the Calligonum mongolicum complex occupied overlapping flowering periods and had consistent pollination agents. Their breeding systems are all self-compatible, tend to be out-crossing and they interbreed amongst each other (out-crossing index, OCI = 4).The crosses within and amongst species had high seed sets (44 - 65%). Phylogenetic analyses of Calligonum sect. Medusae and the network analysis of nrDNA (ITS and ETS) in the complex suggest interbreeding amongst “species” within the complex and provide evidence for taxonomically merging the five species in the complex. The detected hybridisation, occurring within the complex, suggests the need to improve traditional methods of ex situ plant conservation in botanical gardens for maintaining genetic diversity of Calligonum within and amongst species from different geographic areas.

Highlights

Calligonum L. is widely distributed in Northern Africa, Southern Europe and Western and Central Asia (Bao and Alisa 2003)
Five species of the Calligonum mongolicum complex (C. mongolicum, C. pumilum, C. chinense, C. alashanicum and C. zaidamense) were selected by the authors, leaving out the tetraploid C. roborowskii. These selected species were brought to Turpan Eremophytes Botanical Garden (TEBG) from their natural habitats during 2011 to 2013 and were planted in the germplasm garden of Calligonum (Table 2, Qi and Pan 2010; Shi et al 2013)
The bisexual flowers occur in groups of two to four in assimilating branches of the Calligonum species

Summary

Introduction

Calligonum L. is widely distributed in Northern Africa, Southern Europe and Western and Central Asia (Bao and Alisa 2003) It is the only genus in Polygonaceae that contains C4 species 2000) with rapid rates of evolution and diversification (Mabberley 2008) The taxonomy of this genus is complex (Xu 1998) and that of the Calligonum mongolicum Turcz. (1927) of the complex occur within the geographic range of C. mongolicum (Losinskaja 1927; Bao and Grabovskaya-Borodina 2003) All of these more narrowly ranged species were merged into C. mongolicum based on the variation of their fruit characters and the chromosome numbers (Soskov 1975a, 1975b). Analyses of the reproductive biology of the complex are important for resolving the taxonomy and exploring the evolutionary processes (Stebbins 1950; Grant 1992, 1994; Oldfield 2009)

Methods

Results

Conclusion