Genetic analysis and clonal stability of two yellow cypress clonal populations in British Columbia

Genetic analysis of height and form at age 12 years of 697 yellow cypress (Callitropsis nootkatensis [D. Don] Oerst.) clones tested across seven sites in coastal British Columbia (BC) were explored in populations: Population 1 - No Pedigree and Population 2 - Reconstructed Pedigree. Genetic variances were statistically significant but generally higher σ̂_g² was observed for Population 2. Height and form were under low to moderate genetic control as indicated by clonal repeatability and estimates were relatively similar between populations. For example, average Ĥ² in Population 2 was 0.31 for height (range: 0.18-0.45) and 0.22 for form (range: 0.06-0.32). While average Ĥ² in Population 1 was 0.25 for height (range: 0.19-0.35) and 0.18 for form (range: 0.09-0.27). The reconstructed pedigree in Population 2 allowed partitioning the genetic variance (σ̂_g²) into component parts of additive (σ̂_a²), specific combining ability (σ̂_s² ), and clone (σ̂_c² ); however, general lack of structure within the population resulted in variance components to be estimated with little precision for additive and specific combining ability. The majority of genetic variation was associated with clone for both traits. For example, σ̂_c² accounted for 57.6% and 62.5% of the total genetic variance for height and form, respectively. Growth and form responses of clones across test environments were relatively stable and overall type-B genetic correlations were in excess of 0.8 for both traits implying clones selected for production populations should respond favorably across the seed planning zone for yellow cypress in coastal BC.