title: Fine-scale geographical structure of genetic diversity in inland wild beet populations.
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 (B. vulgaris ssp. vulgaris) hybridize easily with their wild relatives (B. vulgaris 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 B. vulgaris 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.
authors.affiliation: Laboratoire de Génétique et Evolution des Populations Végétales, UMR CNRS 8016, Bâtiment SN2, Université des Sciences et Technologies de Lille - Lille 1, F-59655 Villeneuve d'Ascq Cedex, France. jean-francois.arnaud@univ-lille1.fr
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Arnaud
authors.forename: Stéphane
authors.initials: S
authors.lastname: Fénart
authors.forename: Cécile
authors.initials: C
authors.lastname: Godé
authors.forename: Sylvie
authors.initials: S
authors.lastname: Deledicque
authors.forename: Pascal
authors.initials: P
authors.lastname: Touzet
authors.forename: Joël
authors.initials: J
authors.lastname: Cuguen
mesh_terms: D027461:Beta vulgaris / Q000235:genetics*; D018556:Crops, Agricultural / Q000235:genetics; D003593:Cytoplasm / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D005602:France; D051456:Gene Flow; D005819:Genetic Markers; D014644:Genetic Variation; D005828:Genetics, Population; D018745:Genome, Plant; D005843:Geography; D006824:Hybridization, Genetic; D015810:Linkage Disequilibrium; D017422:Sequence Analysis, DNA
chemical_list: D018744:DNA, Plant; D005819:Genetic Markers