Evaluation of somatic embryogenesis for clonal propagation of western white pine

A multiyear program was undertaken to develop a somatic embryogenesis system for clonal propagation of western white pine (Pinus monticola Dougl.). Developing seeds were used to initiate embryogenic lines from families used in blister-rust (Cronartium ribicola J.C. Fisch.) resistance breeding programs in British Columbia. The most responsive seeds contained zygotic embryos ranging in development from late cleavage polyembryony to the early dominance 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-benzyladenine (BA) at 2.25 muM. Proliferation of embryogenic tissue was enhanced by culturing tissue as a thin layer on filter paper supports. Approximately 300 lines representing 18 open- and control-pollinated families were cryopreserved. The highest number of mature somatic embryos was obtained on maturation 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 greenhouse.