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Overview of the timeline for the SE process steps monitored in the study. Germination of embryos for 8-12 weeks in darkness at different temperatures between 2 C to 20 C. Step 1: plant growth for 8 weeks under LED light (50-400 micromol m-2s-1 24 h) at 15 C. Step 2: plant growth after transplanting into peat plugs for 8 weeks under LED light (180-200 micromol m-2 s-1, 24 h) at 25 C. Step 3: plant growth for 3 years in a commercial nursery with natural light. The measurements carried out at each step are defined under the blue arrows.
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A central step is moving plants in plugs to the commercial nursery (in vitro step 2 to ex vitro step 3;  Figures 2  and  8 ).
Percentage of germinated embryos after 11 weeks. (A) Average germination frequency in percentage across all nine clones in response to germination temperature and initial embryo quality score. (B) Average germination for each clone in percentage as response to temperature treatments (average performance of clones showed by dashed line). (C) Average germination for each clone in percentage as response to initial embryo quality score (average across clones showed in bars). (D) Average germination for each clone in percentage as function of frequency of percent high quality initial embryos (percent score 8 + 9).
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Although initial embryo quality was evaluated in the same way for all clones and there was a strong general trend of improved germination with higher initial embryo quality scores, clones showed large differences in successful germination even from similar initial embryo scores ( Figure 3C ) and for similar proportions of high-quality embryos ( Figure 3D ).
(A) Average survival for each clone in percentage at the end of nursery growth (black), mortality during 8 weeks of plant growth in plugs (blue) and 3 years of plant growth in the nursery (green). (B) Average survival of each clone (at the end of nursery growth) as a function of percentage high quality embryos (score 8-9) across all treatments. (C) Average survival across treatments at the end of nursery growth as a function of week of germination (dashed line) and for each initial embryo score (average across all clones and treatments). Weeks 10 and 11 are grouped together due to few observations.
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Additionally, the early-germinated embryos seem to have the best subsequent development irrespective of embryo score and clone ( Figure 6C ).
Results from statistical analyses of covariance (ANCOVA) describing how important each effect is for the trait of interest during steps 1 to 3. Colors describes probability levels (significance) of F-tests for each factor or covariate: Green <0.1%, orange 0.1-0.99, yellow 1-4.99%, light grey 5-10%, grey >10%.
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A central step is moving plants in plugs to the commercial nursery (in vitro step 2 to ex vitro step 3;  Figures 2  and  8 ).
(A) Height growth in nursery (step 3) as function of vitality score (step 2). (B) Survival in percentage in the nursery (during step 3) as a function of vitality score (step 2). (C) Height after 3-years in the nursery (step 3) as a function of number of needles at end of first 8 weeks of autotrophic growth (step 1). (D) Survival in the nursery in percentage (during step 3) for score classes of root development at the end of first 8 weeks of autotrophic growth (step 1).
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Only transferring fully green plants having at least five needles or above (vitality score 6+;  Figure 9B ) will result in a survival rate of close to 80% after the nursery step. Similarly, number of needles at end of the first part of in vitro autotrophic growth (step1) was strongly related to height-growth (step 3;  Figure 9C ).