Abstract
The recalcitrance of adult conifer tissues has prevented vegetative propagation of trees with known and desired characteristics. Somatic embryogenesis (SE) initiation protocol, recently developed for white spruce (Picea glauca, Klimaszewska et al., 2011), was applied in order to examine the feasibility, frequency and timing of SE induction from primordial shoots (PS) of Norway spruce (P. abies). In total, 39 genotypes were screened from 2015 to 2017 using 4–6 years old trees of SE origin as explant donors. Two genotypes responded: 11Pa3794 produced six proliferating embryonal mass (EM) sublines and 11Pa4066 produced 23 EM sublines. SE initiations occurred at the beginning of April, when the temperature sum (d.d.) started to accumulate, and at the end of October or beginning of November when the chilling unit (ch.u.) sum was over 500. EM sublines from both genotypes contained numerous early somatic embryos as detected by acetocarmine staining. The sublines of 11Pa4066 produced the mean of 78.6 ± 12.8 cotyledonary somatic embryos /g FW, but 11Pa3794 produced only a few cotyledonary somatic embryos that were able to germinate. The original EM lines (from which the trees were regenerated) had produced the same number of somatic embryos in 2011 maturations, which was approximately 120 somatic embryos /g FW. Microsatellite analyses conducted with both responsive genotypes confirmed the genetic stability of the EM sublines compared with the donor trees growing in the field. SE protocol developed for white spruce PS explants was also suitable for PS of Norway spruce if the explants were in the responsive developmental stage.
Highlights
Vegetative, i.e., asexual propagation enables production of plants of uniform quality and with known, selected characters
Shoot buds were collected on April 12 and dissected 3 days later (Table 1)
From the spring 2016 collections, six primordial shoots (PS) of 11Pa4066 responded positively (Figures 2D–F and Table 1) and in total 17 embryonal mass (EM) sublines were established in culture
Summary
Vegetative, i.e., asexual propagation enables production of plants of uniform quality and with known, selected characters. Somatic embryogenesis (SE) has become the method of choice for vegetative propagation of conifers (Sutton, 2002) due to its high multiplication rate and the maintenance of juvenility of cell lines via cryopreservation. In the case of Norway spruce, development of cost-efficient vegetative propagation techniques is especially important, Somatic Embryogenesis From Spruce Primordial Shoots since there is shortage of high-quality, bred forest regeneration materials due to irregular flowering of the species, as well as pest and pathogen problems hindering seed production in the seed orchards. The major drawback of the current SE methodology has been that embryogenic cultures can only be initiated from juvenile plant explants, in practice from zygotic embryos, meaning that mature trees with known characteristics cannot be propagated via SE (Bonga et al, 2010). In combination with cost-efficient mass propagation, this would have an enormous impact on forestry with subsequently increased productivity and/or production of tailored raw materials for special end-uses and for landscaping and Christmas tree production
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