Evaluation of somatic embryogenesis for clonal propagation of western white pine

A multiyear program was undertaken to develop a somatic embryogenesis syste m for clonal propagation of western white pine (Pinus monticola Dougl.). De veloping seeds were used to initiate embryogenic lines from families used i n blister-rust (Cronartium ribicola J.C. Fisch.) resistance breeding progra ms in British Columbia. The most responsive seeds contained zygotic embryos ranging in development from late cleavage polyembryony to the early domina nce stage. Overall, 14 of 15 open-pollinated families produced embryogenic lines. The best results (0.8-6.7% initiation) were obtained using modified Litvay medium with 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzyladeni ne (BA) at 2.25 muM. Proliferation of embryogenic tissue was enhanced by cu lturing tissue as a thin layer on filter paper supports. Approximately 300 lines representing 18 open- and control-pollinated families were cryopreser ved. The highest number of mature somatic embryos was obtained on maturatio n medium containing 120 muM abscisic acid, 180 mM sucrose, and 1.0% gellan gum. Of 61 lines tested on this medium, 77% produced mature somatic embryos . In vitro germination and early growth occurred at a high frequency (90-95 %), and plants from 45 genotypes were subsequently transferred to a greenho use.