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Fine-scale geographical structure of genetic diversity in inland wild beet populations

Authors

  • JEAN-FRANÇOIS ARNAUD,

    1. Laboratoire de Génétique et Évolution des Populations Végétales, UMR CNRS 8016, Bâtiment SN2, Université des Sciences et Technologies de Lille – Lille 1, F-59655 Villeneuve d’Ascq Cedex, France
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  • STÉPHANE FÉNART,

    1. Laboratoire de Génétique et Évolution des Populations Végétales, UMR CNRS 8016, Bâtiment SN2, Université des Sciences et Technologies de Lille – Lille 1, F-59655 Villeneuve d’Ascq Cedex, France
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  • CÉCILE GODÉ,

    1. Laboratoire de Génétique et Évolution des Populations Végétales, UMR CNRS 8016, Bâtiment SN2, Université des Sciences et Technologies de Lille – Lille 1, F-59655 Villeneuve d’Ascq Cedex, France
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  • SYLVIE DELEDICQUE,

    1. Laboratoire de Génétique et Évolution des Populations Végétales, UMR CNRS 8016, Bâtiment SN2, Université des Sciences et Technologies de Lille – Lille 1, F-59655 Villeneuve d’Ascq Cedex, France
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  • PASCAL TOUZET,

    1. Laboratoire de Génétique et Évolution des Populations Végétales, UMR CNRS 8016, Bâtiment SN2, Université des Sciences et Technologies de Lille – Lille 1, F-59655 Villeneuve d’Ascq Cedex, France
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  • JOËL CUGUEN

    1. Laboratoire de Génétique et Évolution des Populations Végétales, UMR CNRS 8016, Bâtiment SN2, Université des Sciences et Technologies de Lille – Lille 1, F-59655 Villeneuve d’Ascq Cedex, France
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  • All the authors are involved in population genetic studies of plant species, with a special interest in the evolution of mating system in plants and in its consequences on patterns of spatial genetic structure. More information about the activities of the ‘Laboratoire de Génétique et Evolution des Populations Végétales’ can be found in the following web site: http://www.univ-lille1.fr/gepv/.

Jean-François Arnaud, Fax: +33 3 20 43 69 79; E-mail: jean-francois.arnaud@univ-lille1.fr

Abstract

Introgression arising from crop-to-wild gene flow provides novel sources of genetic variation in plant species complexes. Hybridization within the Beta vulgaris species complex is of immediate concern; crop lineages (Bvulgaris ssp. vulgaris) hybridize easily with their wild relatives (Bvulgaris ssp. maritima) thereby threatening wild beet gene diversity with genetic swamping. Hybridization ‘hotspots’ occur in European seed production areas because inland ruderal wild beets occur and reproduce in sympatry with cultivated beets. We studied gene flow occurring between seed-producing cultivars and ruderal wild Bvulgaris in southwestern France to determine whether feral beets, arising from unharvested cultivated seed, represent an opportunity for crop-to-wild gene flow. We surveyed 42 inland ruderal beet populations located near seed production fields for nucleo-cytoplasmic variation and used a cytoplasmic marker diagnostic of cultivated lines. Occurrence of cultivated-type cytoplasm within ruderal populations clearly reflected events of crop seed escape. However, we found no genetic signatures of nuclear cultivated gene introgression, which suggests past introgression of cultivated cytoplasm into a wild nuclear background through seed escape rather than recent direct pollen flow. Overall, patterns of genetic structure suggested that inland ruderal wild beet populations act as a metapopulation, with founding events involving a few sib groups, followed by low rates of seed or pollen gene flow after populations are established. Altogether, our results indicate that a long-lived seed bank plays a key role in maintaining cultivated-type cytoplasm in the wild and highlight the need for careful management of seed production areas where wild and cultivated relatives co-occur.

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