Mass propagation of Fraser fir [Abies fraseri (Pursh) Poir], a valuable Christmas tree species in the United States, is problematic because methods currently used are inadequate. According to our results with somatic embryogenesis, the culturing methods used with other Abies species are applicable to Fraser fir. Stage 1 somatic embryogenic callus, characterized by suspensor cells and embryo heads, was obtained at low frequency using Schenk and Hildebrandt medium supplemented with 5 mm glutamine, 0.05% casein hydrolysate, 0.01% myoinositol, 2% sucrose, 5 μM benzyladenine, and 0.6% agar. The developmental stage of the embryo was important; embryogenic callus was obtained only with immature, precotyledonary embryos, not with fully formed embryos. Cold storage of cones containing immature embryos inhibited callus proliferation. Genotype was significant in that 35 of 44 families tested proliferated callus; however, only one embryo within one family continued proliferation to produce stage 1 embryogenic callus. Fully formed somatic embryos were not produced because the callus did not continue to proliferate. Although these experiments met with only limited success, they demonstrate the potential for somatic embryogenesis in Fraser fir and the general applicability of methods used with other Abies species.
Nirmala Rajbhandari and Anne-Marie Stomp
Ben A. Bergmann, Ying-Hsuan Sun and Anne-Marie Stomp
Information was obtained concerning appropriate bud harvest time and nitrogen source to be used in the tissue culture of Fraser fir [Abies fraseri (Pursh) Poir] apical buds from 2-year-old seedlings. April was the preferred time to harvest buds for culture, as summer buds had a high contamination frequency, and fall and winter buds did not develop well. Shoot elongation of buds collected in April (1.6 cm) was more than twice that of buds collected in February (0.7 cm) after 100 days in culture; during the same period, shoot fresh mass increased 5-fold (0.21 g in April, 0.04 g in February). Inclusion of a nitrate source reduced the frequency of bud browning, and glutamine was superior to ammonium as a source of reduced nitrogen. Litvay's basal medium containing 10 mm glutamine and 10 mm nitrate was the best nitrogen source combination tested when considering bud browning frequency and shoot fresh mass and length after 100 days in culture.