title: Evaluation of reproductive barriers contributes to the development of novel interspecific hybrids in the Kalanchoë genus.
abstract: BACKGROUND
  Interspecific hybridization is a useful tool in ornamental breeding to increase genetic variability and introduce new valuable traits into existing cultivars. The successful formation of interspecific hybrids is frequently limited by the presence of pre- and post-fertilization barriers. In the present study, we investigated the nature of hybridization barriers occurring in crosses between Kalanchoë species and evaluated possibilities of obtaining interspecific hybrids.
  
  
  RESULTS
  The qualitative and quantitative analyses of pollen tube growth in situ were performed following intra- and interspecific pollinations. They revealed occurrence of pre-fertilization barriers associated with inhibition of pollen germination on the stigma and abnormal growth of pollen tubes. Unilateral incongruity related to differences in pistil length was also observed. The pollen quality was identified as a strong factor influencing the number of pollen tubes germinating in the stigma. In relation to post-fertilization barriers, endosperm degeneration was a probable barrier hampering production of interspecific hybrids. Moreover, our results demonstrate the relation of genetic distance estimated by AFLP marker analysis of hybridization partners with cross-compatibility of Kalanchoë species. At the same time, differences in ploidy did not influence the success of interspecific crosses.
  
  
  CONCLUSIONS
  Our study presents the first comprehensive analysis of hybridization barriers occurring within Kalanchoë genus. Reproductive barriers were detected on both, pre- and post-fertilization levels. This new knowledge will contribute to further understanding of reproductive isolation of Kalanchoë species and facilitate breeding of new cultivars. For the first time, interspecific hybrids between K. nyikae as maternal plant and K. blossfeldiana as well as K. blossfeldiana and K. marnieriana were generated.
authors.affiliation: Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Højbakkegård Allé 9-13, DK-2630, Taastrup, Denmark. kku@plen.ku.dk.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kuligowska
authors.affiliation: Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Højbakkegård Allé 9-13, DK-2630, Taastrup, Denmark. hlm@plen.ku.dk.
authors.forename: Henrik
authors.initials: H
authors.lastname: Lütken
authors.affiliation: AgroTech A/S, Inst. f. Agri Technology and Food Innovation, Højbakkegård Allé 21, DK-2630, Taastrup, Denmark. brc@agrotech.dk.
authors.forename: Brian
authors.initials: B
authors.lastname: Christensen
authors.affiliation: Department of Mathematical Sciences, Faculty of Science, University of Copenhagen, Universitetsparken 5, DK-2100, København Ø, Denmark. ims@math.ku.dk.
authors.forename: Ib
authors.initials: I
authors.lastname: Skovgaard
authors.affiliation: Institute for Plant Genetics, Leibniz Universität Hannover, Herrenhaeuser Str. 2, D-30419, Hannover, Germany. linde@genetik.uni-hannover.de.
authors.forename: Marcus
authors.initials: M
authors.lastname: Linde
authors.affiliation: Institute of Horticultural Production Systems, Leibniz Universität Hannover, Herrenhaeuser Str. 2, D-30419, Hannover, Germany. traud.winkelmann@zier.uni-hannover.de.
authors.forename: Traud
authors.initials: T
authors.lastname: Winkelmann
authors.affiliation: Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Højbakkegård Allé 9-13, DK-2630, Taastrup, Denmark. ren@plen.ku.dk.
authors.forename: Renate
authors.initials: R
authors.lastname: Müller
mesh_terms: D003433:Crosses, Genetic; D035264:Flowers / Q000235:genetics; D014644:Genetic Variation; D005838:Genotype; D018525:Germination; D006824:Hybridization, Genetic; D031962:Kalanchoe / Q000033:anatomy & histology / Q000166:cytology / Q000235:genetics* / Q000502:physiology*; D010802:Phylogeny; D053205:Pollen Tube / Q000254:growth & development; D012098:Reproduction; D012639:Seeds / Q000235:genetics / Q000254:growth & development; D013045:Species Specificity