Abstract
Somatic embryo quality is still a problem for many researchers. To improve the efficiency of germination, special procedures are used, such as partial drying of somatic embryos at high relative humidity or desiccation in the presence of supersaturated solutions of salt. In this work, cotyledonary somatic embryos of Norway spruce (Picea abies) and Serbian spruce (P. omorika) were placed on culture media (ME or BM-5) to germinate. We found that after 4 weeks of incubation on these media, hypocotyl and radicle growth of control (non-dried) somatic embryos of both species was not adequate to yield seedlings able to acclimatize to greenhouse conditions. Therefore, somatic embryos were partly dried at relative humidity of 97 % or desiccated at relative humidity of 79 %, for 2 or 3 weeks, and then placed on the Margara (ME) medium. Partial drying of somatic embryos at the higher relative humidity (97 %) enabled an improvement of radicle growth of germinating somatic embryos in both species. The highest conversion rate (45 %) was obtained for embryos of Norway spruce maintained for 2 weeks at relative humidity of 97 %. This treatment contributed to the improvement of germination and conversion efficiency of somatic embryos of Norway spruce, regardless of the drying period. Improved radicle growth facilitated development of better quality seedlings of this spruce species. In Serbian spruce, we did not obtain seedlings of sufficient quality, due to poor hypocotyl growth. Desiccation at humidity of 79 % for 3 weeks proved to be lethal to somatic embryos of both species.
Highlights
Somatic embryogenesis is an alternative to traditional methods of tree propagation
We found that after 4 weeks of incubation on these media, hypocotyl and radicle growth of control somatic embryos of both species was not adequate to yield seedlings able to acclimatize to greenhouse conditions
The aim of our study was to determine the effect of the two selected culture media, partial drying at high relative humidity, and desiccation, on germination and conversion of somatic embryos of two spruce species into seedlings
Summary
Somatic embryogenesis is an alternative to traditional methods of tree propagation (from seeds or vegetatively). It makes a lot of genetically valuable plant material available in a short time. Proper germination of somatic embryos enables their conversion into seedlings. The conversion of embryos into somatic seedlings is indicated by development of both functional radicle and shoot system (Hay and Charest 1999). This is a key step to the transfer of plants from in vitro culture to natural conditions. The quality of somatic seedlings is largely determined by nutritional, physical and chemical conditions applied during the successive stages of somatic embryogenesis (Lazzeri et al 1987).
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