Physiological and morphological differences between somatic, in vitro germinated, and normal seedlings of red spruce (Picea rubens Sarg.)
Growth and foliar characteristics of red spruce (Picea rubens Sarg.) seedlings produced from somatic embryos (SS) from cell lines representing three genotypes, zygotic embryos (ZS) germinated in vitro, and normal seed (NS) germinated in a greenhouse were compared after 8 months of growth in the greenhouse. NS and SS were similar in terms of height, diameter, root to shoot ratio, and total plant dry mass, but ZS grew significantly more. The root to shoot ratio of ZS was only one half that of SS and NS. Foliar characteristics such as needle dry mass and specific leaf area were also similar between SS and NS and appeared to be distinctly juvenile, but were the most juvenile in ZS. Net photosynthesis, stomatal conductance, and total chlorophyll content were lowest in the ZS, even though they grew the most. After 2 years of growth in pots outdoors, the stem diameter of ZS was still significantly greater than that of SS or NS, although height growth was no longer significantly different. There was no evidence that SS showed signs of accelerated maturation. The possibility that the unexpectedly greater growth of ZS is due to environmental variation during seed set and early germination that affects subsequent seedling growth and development is discussed.