Breeding systems, hybridization and continuing evolution in Avon Gorge Sorbus

Shanna Ludwig, Ashley Robertson, Timothy C. G. Rich, Milena Djordjevic, Radosav Cerovic, Libby Houston, Stephen A. Harris, Simon J. Hiscock*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

34 Citations (Scopus)

Abstract

Interspecific hybridization and polyploidy are key processes in plant evolution and are responsible for ongoing genetic diversification in the genus Sorbus (Rosaceae). The Avon Gorge, Bristol, UK, is a world hotspot for Sorbus diversity and home to diploid sexual species and polyploid apomictic species. This research investigated how mating system variation, hybridization and polyploidy interact to generate this biological diversity.

Mating systems of diploid, triploid and tetraploid Sorbus taxa were analysed using pollen tube growth and seed set assays from controlled pollinations, and parentoffspring genotyping of progeny from open and manual pollinations.

Diploid Sorbus are outcrossing and self-incompatible (SI). Triploid taxa are pseudogamous apomicts and genetically invariable, but because they also display self-incompatibility, apomictic seed set requires pollen from other Sorbus taxa a phenomenon which offers direct opportunities for hybridization. In contrast tetraploid taxa are pseudogamous but self-compatible, so do not have the same obligate requirement for intertaxon pollination.

The mating inter-relationships among Avon Gorge Sorbus taxa are complex and are the driving force for hybridization and ongoing genetic diversification. In particular, the presence of self-incompatibility in triploid pseudogamous apomicts imposes a requirement for interspecific cross-pollination, thereby facilitating continuing diversification and evolution through rare sexual hybridization events. This is the first report of naturally occurring pseudogamous apomictic SI plant populations, and we suggest that interspecific pollination, in combination with a relaxed endosperm balance requirement, is the most likely route to the persistence of these populations. We propose that Avon Gorge Sorbus represents a model system for studying the establishment and persistence of SI apomicts in natural populations.

Original languageEnglish
Pages (from-to)563-575
Number of pages13
JournalAnnals of Botany
Volume111
Issue number4
DOIs
Publication statusPublished - Apr 2013

Keywords

  • HYBRID SPECIATION
  • POLLEN-PART MUTANTS
  • CRATAEGUS ROSACEAE
  • POLYPLOID PLANTS
  • GENETIC DIVERSITY
  • Sorbus
  • L. ROSACEAE
  • Hybridization
  • evolution
  • apomixis
  • BRITISH-ISLES
  • polyploidy
  • self-incompatibility
  • SEED DEVELOPMENT
  • pseudogamy
  • GAMETOPHYTIC SELF-INCOMPATIBILITY
  • SENECIO-CAMBRENSIS

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