Journal Article

Eco-geographically divergent diploids, Caucasian clover (<i>Trifolium ambiguum</i>) and western clover (<i>T. occidentale</i>), retain most requirements for hybridization

Warren M. Williams, Isabelle M. Verry, Helal A. Ansari, S. Wajid Hussain, Ihsan Ullah, Michelle L. Williamson and Nicholas W. Ellison

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 108, issue 7, pages 1269-1277
Published in print November 2011 | ISSN: 0305-7364
Published online August 2011 | e-ISSN: 1095-8290 | DOI: https://dx.doi.org/10.1093/aob/mcr226
Eco-geographically divergent diploids, Caucasian clover (Trifolium ambiguum) and western clover (T. occidentale), retain most requirements for hybridization

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  • Ecology and Conservation
  • Evolutionary Biology
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Background and Aims

DNA sequence similarities and hybridization patterns in Trifolium (clovers) section Trifoliastrum suggest that rapid radiation from a common ancestral source led to this complex of diverse species distributed across Europe, western Asia and North Africa. Two of the most geographically and ecologically divergent of these species are the rhizomatous T. ambiguum from high altitudes in eastern Europe and western Asia and the stoloniferous T. occidentale from sea level in western Europe. Attempts were made to hybridize these species to ascertain whether, despite this separation, gene flow could be achieved, indicating the retention of the genetic factors necessary for hybridization.

Methods

Three F1 hybrids formed after embryo rescue were described, characterized by conventional and molecular cytogenetics, subjected to fertility tests and progeny generations were developed.

Results and Conclusions

Partially fertile hybrids between Trifolium ambiguum and T. occidentale were obtained for the first time. The F1 hybrids produced seeds after open-pollination, and also produced triploid progeny in backcrosses to T. occidentale from the functioning of unreduced gametes in the hybrids. These plants were fertile and produced progeny with T. occidentale and with T. repens. Meiotic chromosome pairing in the F1 showed six to eight bivalents per pollen mother cell, indicating pairing between the parental genomes. A chromosome-doubled form of one hybrid, produced using colchicine, showed some multivalents, indicative of interspecific chromosome pairing. The hybrid plants were robust and combined phenotypic characteristics of both species, having stolons, thick roots and a few rhizomes. Results show that despite separation by the entire breadth of Europe, the speciation process is incomplete, and these taxa have partially retained most of the genetic compatibilities needed for hybridization (possibly except for endosperm development, which was not tested). The fertile progeny populations could lead to new clover breeding strategies based on new hybrid forms.

Keywords: Trifolium ambiguum; T. occidentale; T. repens; interspecific hybridization; Caucasian clover; western clover; white clover; introgression; genetic bridge; unreduced gametes; speciation

Journal Article.  7026 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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