The ontogenetic course followed by somatic embryos of interior spruce is highly dependent on the media concentration of abscisic acid (ABA). Little or no organized development occurs in the absence of ABA and as the level of ABA is increased, a range of embryo types is produced. “Shooty embryo” structures predominate in many callus lines at low levels of ABA (1‐10 μM), while 10‐20 μM ABA promotes the formation of bipolar embryos that germinate precociously. When ABA is increased to 30‐40 μM, precocious germination is inhibited and opaque cotyledonary embryos characteristic of their zygotic counterparts are formed which enter a period of quiescence. Only “mature” somatic embryos contain significant amounts of storage proteins and the level to which these proteins accumulate is dependent on the concentration of ABA. Indole‐butyric acid (IBA) included with ABA increases the number of mature embryos. Root elongation, which was used as a measure of embryo quality, was never observed from shooty embryo Structures and was 2‐3 fold higher in mature embryos compared to those that germinated precociously.

To apply somatic embryogenesis to clonal propagation of forest species, the technique must be applicable to a broad range of genotypes and allow efficient regeneration of phenotypically normal plants. Seventy-one lines (genotypes) of embryogenic cultures from six open-pollinated families were obtained by culturing immature embryos of interior spruce. Interior spruce represents a mixture of two closely related species, Piceaglauca (Moench) Voss and Piceaengelmannii Parry, from the interior of British Columbia where they hydridize with one another. The abscisic acid dependent developmental profile (the proportion of rooty embryos, shooty embryos, precociously germinating embryos, and mature embryos over a range of abscisic acid concentrations) differed among genotypes, but in general, production of mature somatic embryos was highest at 40 and 60 μM abscisic acid. Treatment of mature embryos with a high relative humidity treatment resulted in partial drying of the embryos and upon rehydration, markedly enhanced germination of the eight genotypes tested. Within 1 week of being placed under germination conditions, somatic embryos treated with the high relative humidity treatment showed 80–100% germination for 12 of the genotypes, and most genotypes had germination rates of greater than 40%. Survival of "emblings" (germinants from somatic embryos) following transfer to soil, acclimatization, and first season's growth in the nursery was 80% or greater for most genotypes. Over 1200 emblings were tested for nursery performance, representing the first large-scale evaluation of conifer somatic embryos under exvitro conditions. Growth rates, final height, shoot and root morphology, and frost hardiness were similar for emblings and seedlings following the first growing season. These results indicate that somatic embryogenesis can be used for the production of planting stock for a range of interior spruce genotypes.

No abstract

Zygotic embryos of Piceaglauca (Moench) Voss from five half-sib seed families and P. engelmanii Parry from one half-sib family, collected on July 13 and 27 and August 24, were cultured in the presence of 2,4-dichlorophenoxyacetic acid, N6-benzyladenine, and sucrose ranging from 0.5 to 4% for the induction of embryogenic callus and the production of stable embryogenic callus lines. Embryogenic callus was induced from all three collections with all seedlots. The July 13 collection was two to four times more embryogenic than the later collections. Embryogenic callus was induced at all sucrose levels, but 4% sucrose was clearly inferior, whereas 1% was best overall. Factors that favored the induction of embryogenic callus also favored the production of stable embryogenic callus lines. There was a 40% decline in callus line establishment compared with embryogenic callus induction and some seed lots failed to yield embryogenic lines from the two later collections. The formation of caulogenic callus was promoted at 3 and 4% sucrose. Embryos from the August 24 collection were more caulogenic than those from the earlier collections.

Somaclonal variation during interior spruce (Picea glauca engelmannii complex) somatic embryogenesis was evaluated using culture morphology and isozyme analysis. Genotype-specific abscisic acid-dependent developmental profiles and isozyme patterns were similar for subclone and parent line embryogenic cultures and cotyledonary somatic embryos. Extensive analysis of fifteen hundred subclone embryos of one genotype revealed no isozyme pattern variation. Initiation of embryogenic cultures was dependent on the developmental stage of the explant although cultures derived from different stages were morphologically similar. The embryogenic cultures initiated from interior spruce embryos show a high degree of genetic stability in that the morphological behavior and isozyme phenotype were always consistent with that of the explant genotype. These results support the conclusion that this culture system is appropriate for clonal propagation of interior spruce.