EFFECTS OF GELLING AGENTS, AMMONIUM-NITRATE, AND LIGHT ON THE DEVELOPMENT OF PICEA-MARIANA (MILL) BSP (BLACK SPRUCE) AND PICEA-RUBENS SARG (RED SPRUCE) SOMATIC EMBRYOS

Embryogenic tissue was obtained from immature zygotic embryos of black spruce (Picea mariana) and mature zygotic embryos of red spruce (Picea rubens). Embryogenic tissues were induced and maintained on half-strength Litvay's medium supplemented with 10-mu-M 2,4-dichlorophenoxyacetic acid (2,4-D), 5-mu-M benzylaminopurine (BAP), 1 g/l casein hydrolysate, 500 mg/l glutamine, 1.0% (w/v) sucrose, and 0.9% (w/v) Difco Bacto-agar. To improve the maturation of somatic embryos, different gelling agents and ammonium nitrate concentrations were tested with a basal maturation medium consisting of HLM basal medium supplemented with 1 g/l glutamine, 1 g/l casein hydrolysate, 6% (w/v) sucrose, and 7.5-mu-M abscisic acid (ABA). The number of somatic embryos was significantly higher on medium solidified with Gelrite gellan gum than with Difco Bacto-agar. Corn, potato, wheat, or rice starches as gelling agents either did not influence or drastically reduced the development of black spruce somatic embryos. An ammonium nitrate concentration 3.4-10 mM for black spruce or 3.4-15 mM for red spruce was found to be optimal for embryo development. Maintenance of the embryogenic tissue under light or in darkness and use of different fluorescent lamps during the maturation stage did not influence the total number of black spruce somatic embryos produced. However, a maximum number of germinating embryos was produced when the embryogenic tissue was maintained in darkness, followed by a maturation stage in light.