Optimized somatic embryogenesis in Pinus strobus L.

Somatic embryogenesis (SE) initiation in Pinus strobus was optimized by the manipulation of plant growth regulator (PGR) concentrations in the culture medium. Modified Litvay medium (MLV) of Litvay et al. (1985) supplemented with lower than routinely used PGR concentration increased initiation of es tablished embryogenic cultures from approximately 20 to 53%. The original d evelopmental stage of zygotic embryos had a pronounced effect on the SE res ponse. The Optimum stage was the pre- to shortly post-cleavage stage. A sub stantial genetic influence on initiation of SE was indicated by a significa nt variance component due to families. Genotype X collection date and genot ype X media interactions had large effects on initiation of SE. The PGR lev els in the culture medium prior to maturation had a significant effect on s ubsequent production of mature somatic embryos. Embryogenic tissue initiate d and proliferated on medium with a low level of PGR consistently produced a high number of somatic embryos, indicating that optimized initiation prot ocol also enhanced somatic embryo production. Somatic embryos of 93 embryog enic lines (representing five families) that were initiated on media with d ifferent PGR concentrations were converted to plants at an overall frequenc y of 76%, and grown in the greenhouse. With these improved protocols, appli cation of P. strobus SE in commercial clonal forestry is feasible as an alt ernative to traditional breeding and reforestation.