Field Performance

Somatic seedlings have now been growing for four years on a typical forest regeneration site in Washington State for clonal demonstration purposes. Strikingly uniform growth is apparent for somatic seedlings within a clone (Figure 29.2) compared with the less uniform zygotic seedlings (Figure 29.3). Somatic seedlings from ESM of 20-25 year old trees of Pinus radiata5 and Picea abies4 have also been grown in the field. Morphology of these somatic seedlings, too, was reported to be similar to zygotic seedlings. Recently, we have produced over 30,000 somatic seedlings of Douglas fir from a large number of genotypes for a clonal field test.

flasks. One liter nipple flasks have also been used to bulk up embryogenic suspension cultures of conifers.9 Large scale production of somatic embryos can be achieved in a bioreactor.12 Bioreactors provide several advantages for the growth of embryogenic suspension cultures, including larger volume (than shake flasks), maintenance of more homogeneous cultures, and control of the cultural and physical environment for optimum growth.12 Two to ten liter bioreactors have been used to scale up embryogenic cultures of several conifer species, different types of bioreactors being used for different conifer species.13,14 Maturation has not been achieved for embryos immersed in liquid medium. Recently, cotyledonary embryo development of Sitka spruce has been reported in an airlift bioreactor,15 but their low germination shows that biochemical maturity was not attained. At Weyerhaeuser, ESM cultures of Douglas fir were grown in low speed, winged, magnetically driven stirred bioreactors.16 Their

Fig. 29.2. One replicate plot of clones (from control crossed genetically improved family) of Douglas fir somatic seedlings growing in the field. Photo shows the uniformity of somatic seedlings.

yields of cotyledonary embryos, after plating on pads soaked with development medium, did not differ significantly from flask yields, but their germination was improved.16

Cotyledonary embryos have been produced in a bioreactor using an absorbent pad above the surface of liquid medium.17,18 At Weyerhaeuser, we have produced cotyledonary embryos of Douglas fir in a bioreactor by temporary immersion of the lower pad sur-face.14 Liquid medium was pumped in and out of the bioreactor from a reservoir at different intervals. Higher yields of good quality cotyledonary embryos were produced using this method.14

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