Early selection improves clonal performance and reduces intraclonal variation of Norway spruce plants propagated by somatic embryogenesis

Abstract

Height growth during the first and second growth periods (i.e., the June-September period in consecutive years) and intraclonal variation were assessed in 13 Norway spruce (Picea abies (L.) Karst.) clones propagated by somatic embryogenesis. The plants were acclimatized and grown in a greenhouse until mid-July and then transferred outdoors. The clonal mean heights after the first and second growth periods were lower for somatic embryo plants than for seedlings from corresponding families sown at the time of somatic embryo plant ex vitro transfer, because a large proportion of somatic embryo plants were small. We determined whether certain selection criteria at ex vitro transfer can be used to identify somatic embryo plants with height growth characteristics comparable with those of seedlings. Epicotyl length and presence of lateral roots proved to be important parameters for selection, whereas main root length was less useful. A combined selection for somatic embryo plants with lateral roots and with an epicotyl length exceeding 8 mm resulted in taller plants and reduced intraclonal variation after the first and second growth periods. The growth of somatic embryo plants selected in this way was similar to that of seedlings from the corresponding families. We conclude that selection according to these criteria at ex vitro transfer can result in improved performance of clonal stock propagated by somatic embryogenesis.

Somatic embryogenesis of selected spruce species (Picea abies, P. omorika, P. pungens 'Glauca' and P. breweriana)

“…In micropropagation of coniferous trees, an elimination of auxins and cytokinins from the medium and addition of ABA as well as an increase in osmotic pressure at the stage of maturation of somatic embryos, are necessary for regeneration of cotyledonary embryos. Many researchers found that addition of exogenous ABA to the medium in a suitable concentration affects the number of mature somatic embryos in various species of coniferous trees (Norgaard 1997;Label and Lelu 2000;Percy et al 2000;Stasolla et al 2002;Hogberg et al 2003). Reactions of embryogenic tissues of coniferous trees to ABA are highly varied.…”

Screening RAPD primers to assess clonal fidelity in somatic embryos of Sawara cypress (<i>Chamaecyparis pisifera</i> Sieb. et Zucc.) and field performance of somatic embryo-derived trees

“…For the same species, Cyr et al (1991) reported that the differences between somatic plants and seedlings occurred early during plant development. Although somatic plants were consistently shorter than seedlings after the first growth period, the differences in height decreased by the end of the second growth period (Högberg et al 2003). In contrast, for coastal Douglasfir (Pseudotsuga menziesii var.…”

“…Evidences that culture conditions during somatic embryo development may reduce the growth of somatic plants were reported for several conifers (Högberg et al 2003). Use of PEG and long-term contact with ABA during maturation substantially reduced the growth of regenerated Norway spruce plants von Arnold 1998, Högberg et al 2001).…”

“…In addition, epicotyl length and presence of lateral roots as combined selection criteria at ex vitro transfer could be used to identify somatic plants having height growth characteristics comparable to those of seedlings. Early selection according to these criteria improves clonal performance and reduces intraclonal variation in somatic plants of Norway spruce (Högberg et al 2003).…”

Monozygotic cleavage polyembryogenesis and conifer tree improvement

“…For in vitro cloning technologies, the selection differential, juvenile mature cor relations and the reciprocal of the generation interval are major factors in saving time and capturing genetic gains elite clones were established in the greenhouse for field testing. In Europe, clones produced from PEMs have been field tested for spruce, pine, and other conifers (e.g., Högberg et al, 2003). In North and South America, South east Asia, and New Zealand, sever al industries and governments have scaled up the production of 'somatic seedlings' to commercial volumes.…”