title: Germination failure is not a critical stage of reproductive isolation between three congeneric orchid species.
abstract: OBJECTIVE
  In food-deceptive orchid species, postmating reproductive barriers (fruit set and embryo mortality) have been shown to be more important for reproductive isolation than premating barriers (pollinator isolation). However, currently there is very little knowledge about whether germination failure acts as a reproductive barrier in hybridizing orchid species.
  
  
  METHODS
  In this study, we investigated germination and protocorm development of pure and hybrid seeds of three species of the orchid genus Dactylorhiza. To test the hypothesis that germination failure contributed to total reproductive isolation, reproductive barriers based on germination were combined with already available data on early acting barriers (fruit set and embryo mortality) to calculate the relative and absolute contributions of these barriers to reproductive isolation.
  
  
  RESULTS
  Protocorms were formed in all crosses, indicating that both hybrid and pure seeds were able to germinate and grow into protocorms. Also, the number of protocorms per seed packet was not significantly different between hybrid and pure seeds. High fruit set, high seed viability, and substantial seed germination resulted in very low reproductive isolation (average RI = 0.05). In two of six interspecific crosses, hybrids performed even better than the intraspecific crosses.
  
  
  CONCLUSIONS
  Very weak postmating reproductive barriers were observed between our study species and may explain the frequent occurrence of first-generation hybrids in mixed Dactylorhiza populations. Germination failure, which is regarded as one of the most important bottlenecks in the orchid life cycle, was not important for reproductive isolation.
authors.affiliation: Biology Department, Laboratory of Plant Conservation and Population Biology, University of Leuven, Kasteelpark Arenberg 31, B-3001 Heverlee, Belgium. koen.dehert@bio.kuleuven.be
authors.forename: Koen
authors.initials: K
authors.lastname: De Hert
authors.forename: Olivier
authors.initials: O
authors.lastname: Honnay
authors.forename: Hans
authors.initials: H
authors.lastname: Jacquemyn
mesh_terms: D000465:Algorithms; D003433:Crosses, Genetic; D018525:Germination / Q000235:genetics*; D006823:Hybrid Vigor / Q000235:genetics; D006824:Hybridization, Genetic; D008957:Models, Genetic; D029595:Orchidaceae / Q000145:classification / Q000235:genetics* / Q000254:growth & development; D012098:Reproduction / Q000235:genetics; D060047:Reproductive Isolation; D012639:Seeds / Q000235:genetics* / Q000254:growth & development; D013045:Species Specificity