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Use of somatic or synthetic
seed is of potential interest as a micropropagation tool for superior conifer
genotypes. However, whether naked or encapsulated, the most important criterion
is that the asexual embryo or somatic seed must be able to simulate the zygotic
embryo or true seed. This study attempted a comparison of the somatic embryo
of Norway spruce (Picea abies) with its zygotic counterpart. A major
finding was that the percentage germination of fresh or somatic embryos partially
desiccated at relative humidities of 97% and 63% to moisture contents approaching
those of the seed, was substantially lower. It further declined rapidly with
either cold storage and/or encapsulation. This sensitivity to drying suggests
that the somatic embryo/seed may behave either as an orthodox seed with limited
ability to withstand desiccation or as a recalcitrant seed that cannot survive
drying below a moisture content that is relatively high. As the megagametophyte
contains >80% of the seed's total lipid and protein reserves, the carbon
and amino acid pools available to the zygotic embryo far exceed those accessible
to the somatic embryo. The conclusions are: (1) in Norway spruce the somatic
seed, lacking a suitable artificial megagametophyte, does not simulate the
true seed, and (2) the somatic embryo, if it behaves like an isolated zygotic
embryo cultured in vitro, does so with greatly reduced physiological
vigour.

South African Journal of Botany 2002, 69(2): 176–185