Interior spruce seedlings compared with emblings produced from somatic embryogenesis. I. Nursery development, fall acclimation, and over-winter storage
Interior spruce (Piceaglauca (Moench) Voss × Piceaengelmannii Parry) seedlings and emblings (plants produced via somatic embryogenesis tissue culture) were grown as container 1 + 0 plants. Seedling and embling morphological development was monitored during the growing season. Needle freezing tolerance, days to terminal bud break (DBB1), root growth capacity (RGC), and shoot dry weight fraction (DWF) were monitored during the fall and in frozen storage. Emblings had slower height, diameter, and root growth rates during the initial 2.5 months in the nursery. Thereafter, seedlings and emblings had equal height growth rate, while emblings had greater diameter and root growth rates. At the end of the growing season, seedlings and emblings, respectively, had 23.8 and 14.2 cm shoot height, 4.0 and 3.4 mm diameter, and 0.81 and 0.80 g root dry weight. During the fall, DBB1 of both seedlings and emblings decreased, with emblings having a more rapid decrease. Both seedlings and emblings showed a similar increase in freezing tolerance. Emblings had a greater increase in DWF. During the fall, RGC decreased then increased, with seedlings displaying a greater increase than emblings. While in frozen storage, seedlings and emblings maintained a low DBB1, and a high RGC and DWF. Freezing tolerance decreased while in frozen storage, with the loss more pronounced among seedlings. A degree growth stage model describes the first year cycle of development for seedlings and emblings. Results indicate that seedlings and emblings have slightly different patterns of first year growth and fall acclimation. However, both seedlings and emblings were at the end of rest when lifted for frozen storage.