Preliminary results from five generations of a western redcedar (<Emphasis Type="Italic">Thuja plicata</Emphasis>) selection study with self-mating

A western redcedar selection study with self-mating was initiated using an accelerated breeding cycle, such that five generations were completed in 10 years. Thirty random and 30 selected lines for height, from 15 unrelated full-sib families (S₀; inbreeding coefficient F = 0) were the founders for the subsequent selfed lines (S₁ to S₄; F = 0.5 to 0.9375, respectively). Of the original 60 lines, 50 were still in existence at the S₄ generation. Random extinct lines and replacement seedlings resulted either from a lack of mature cones or filled seed, whereas selected line extinctions and replacements were mostly due to a lack of filled seed. Approximately 47% of parent-trees in the S₄ generation displayed temporal separation of male and female function, as opposed to 7% in the S₀. Observed response to selection in height was approximately 21% after four generations. There were no significant reductions in seed weight or vigor across generations, and these traits were not correlated with selection height. Results are discussed in relation to the general influences of inbreeding and random genetic drift on response to the selection and incorporation of selfing into tree-breeding strategies.