title: Seed dormancy distribution: explanatory ecological factors.
abstract: OBJECTIVE
  Knowledge of those traits that vary with latitude should be helpful in predicting how they may evolve locally under climate change. In the sea beet Beta vulgaris ssp. maritima, seed dormancy largely controls the timing of germination, is highly heritable and varies geographically; it is therefore thought to be selected by climate. The aim here was to characterize the variation in seed dormancy among sea beet populations across the French distribution area, as well as the ecological factors in situ that are correlated with and that could therefore select for seed dormancy. The relative importance of genetic inheritance vs. non-genetic variation is also evaluated.
  
  
  METHODS
  The proportions of dormant seeds from 85 natural populations encompassing different climates over the whole French distribution area were measured under controlled conditions. Germination phenology was observed in a common garden experiment. Dormancy variation of seeds collected in situ was compared with that of seeds collected on plants grown in the greenhouse.
  
  
  RESULTS
  The proportions of dormant seeds in the greenhouse were highly variable, covering almost the entire range from 0 to 1, and followed a geographical pattern from lower dormancy at high latitudes to high dormancy at low latitudes. The distribution of dormancy was positively correlated with yearly temperatures, especially summer temperatures. Minimum temperatures in winter did not significantly explain the trait variation. The genetic component of the total variation was significant and is probably completed by an important adjustment to the local conditions brought about by maternal adaptive phenotypic plasticity.
  
  
  CONCLUSIONS
  Dormancy in sea beet could be interpreted as a way to limit summer germination and spread germination over the first autumn and spring or following autumns. This highly heritable trait has the potential to evolve in the relatively near future because of climate change.
authors.affiliation: Laboratoire Génétique et Evolution des Populations Végétales, UMR 8198, CNRS, Université Lille 1, F-59655 Villeneuve d'Ascq cedex, France.
authors.forename: Kristen
authors.initials: K
authors.lastname: Wagmann
authors.forename: Nina-Coralie
authors.initials: NC
authors.lastname: Hautekèete
authors.forename: Yves
authors.initials: Y
authors.lastname: Piquot
authors.forename: Cécile
authors.initials: C
authors.lastname: Meunier
authors.forename: S Eric
authors.initials: SE
authors.lastname: Schmitt
authors.forename: Henk
authors.initials: H
authors.lastname: Van Dijk
mesh_terms: D000064:Acclimatization; D027461:Beta vulgaris / Q000235:genetics / Q000502:physiology*; D002980:Climate; D016000:Cluster Analysis; D004463:Ecology; D005602:France; D005843:Geography; D018525:Germination; D057445:Plant Dormancy / Q000502:physiology*; D012621:Seasons; D012639:Seeds / Q000235:genetics / Q000502:physiology*; D013696:Temperature; D013997:Time Factors