Outcrossing frequency in selfing and apomictic plant species subject to containment measures in GMO development regulation

This report was commissioned by the COGEM in order to reassess the knowledge basis on outcrossing in the plant species presently categorised as basically having a selfing breeding system in the so-called “Lijst van inhullingsverplichtingen” (“ list of inflorescence bagging regulations”), formerly called “Appendix C”, where all species are listed in which transformation research is performed, together with containment actions deemed necessary per species. Containment measures depend on the type of breeding system of the relevant plant species, and the likelihood of contact with cross-fertile relatives in the Dutch flora.

In the first instance, selfing and apomictic species were regarded as having a negligible likelihood of gene flow by pollen moving out of research facilities. However, with an increasing awareness that selfing plant species rarely are a hundred percent selfing under natural conditions, nor are apomicts likewise a hundred percent apomictic, the Dutch advisory committee on biosafety issues of GMOs (genetically modified organisms) COGEM started to re-evaluate the species on the containment obligations list (“Lijst van inhullingsverplichtingen” or Appendix C) in 2003. This proved not a simple task, for it was not easy to obtain a complete overview of the literature in this area, which is often spread over many old publications that are not easily accessible. Moreover, there are differences in the amount of information available per species. In addition, plant breeders also often were not able to provide a complete and scientifically validated overview of their experiences with their crop species.

Therefore, the present study describes an attempt to provide the best available overview of the present knowledge of outcrossing frequencies in selfing species on the containment list. The study is based on an exhaustive search of the literature and information requests with experts from the scientific and breeding community, including genebank experts.