Definition

Thorpe (1988) defines somatic embryogenesis (SE) as "the development of haploid or diploid cells into differentiated plants through embryo stages without the fusion of gametes".  Ammirato (1983) gives a comparable definition.  Although both authors discuss SE for a number of species the rose is not included.  However Arnold, (unpublished data) obtained SE with the hardy rose ‘Champlain’ and other roses with selected procedures described in the above texts.

Leaf tissue, callus, medium and embryos

Nodal sections from the ‘Champlain’ and other rose genotypes, were propagated on Murashige and Skoog (1962) (MS) culture media and allowed to grow for 3 weeks.  After this time, leaf tissue and petioles were excised from the sections, scored with a scalpel and again placed on an MS medium containing the auxin 2,4-D in petri dishes.  The leaf sections were grown under 16-h cool white fluorescent lights for a period of three weeks.  Friable callus which developed was collected and transplanted to an auxin-free MS medium for a further 3 week period, and then plated onto an MS medium containing a combination of Kinetin and Abscisic acid.  After 5 or 6 weeks embryos developed in the callus tissue which were then transferred to an MS medium in test tubes and allowed to grow into small seedlings.  The seedlings were then transplanted to a substrate and allowed to harden off under mist conditions (Arnold - unpublished data). Although a number of different roses were included in the study, it was evident that more research was required to induce embryogenesis in certain varieties.

Embryo germination

However, Dohm et al., (2001) achieved a measure of success with the roses ‘Heckenzauber’ and ‘Pariser Charme’ using a similar technique but with a combination of NAA, zeatine and GA3 for the embryogenic callus.  According to these authors, of the 50 rose genotypes tested, 69% could be regenerated although they did incur difficulty with "germination" of the SE’s.

In Arnold’s study, the rose plants developed from somatic embryos seemed true-to-form which would possibly be the case even for large numbers of plants derived from SE.  However, Thorpe (1988) and Ammirato (1983) did indicate that somaclonal variation can occur but could be advantageous in the development of new plants.

Readers are referred to Thorpe’s (1988), Ammirato’s (1983) and more recent articles for a thorough treatment of somatic embryogenesis.