Douglas-fir (Pseudotsuga menziesii (Mirb) Franco) is a native conifer from the Pacific North-West of the US and Canada, and is one of the most important timber species used in the world. Douglas-fir is highly productive in a range of climatic conditions and has valuable wood properties (quality) as well as a strong tolerance to diseases and insects. In Europe, Douglas-fir is a major species for reforestation with increasing demand for its wood. Adaptation of new varieties to climate change and associated stresses is one challenging question for ongoing breeding programs. Efficient selection and vegetative propagation of improved varieties are key issues to maintain productivity in plantation forestry (Lelu-Walter et al. 2013), however, as in many other conifers, early maturation is preventing clonal forestry through conventional multiplication methods in Douglas-fir (Bastien et al. 2013). Somatic embryogenesis from immature seeds, coupled with cryopreservation, is a promising retroactive clonal propagation system of selected trees. This technology has been developed for an increasing number of conifer species (Klimaszewska et al. 2016). Excluding patents, there are only a few published studies on Douglas-fir somatic embryogenesis (Durzan and Gupta 1987; Pullman et al. 2005, 2009). One recurrent problem is the sustainable multiplication of initiated embryogenic material, i.e., embryonal masses (EMs). Yellowish, non-embryogenic cells (NEC), which are interspersed with EM, is frequently observed during this process. In this work, we describe EM morphology and cytology (light and confocal microscopy) of different embryogenic lines. A suggested method to reduce the formation of NEC and sustain EM proliferation is presented.
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