Abstract
Summary Seed orchards are the principal delivery method for genetically selected materials to operational reforestation programmes in British Columbia, Canada. Orchard parents are assigned breeding values for the improved trait (e.g. stem volume growth). The genetic quality of orchard seedlots is rated annually by weighting the breeding value of each orchard parent by its proportional gamete contribution (male and female) to the seedlot. Parental gamete contributions are also used to calculate an effective population size to quantify genetic diversity in a seedlot. Adaptation and genetic representation of populations are carefully considered at orchard establishment to ensure minimum seedlot standards are met. The calculation of genetic worth also considers the gamete contribution of non-orchard pollen parents, and is lowered for the negative effects of contaminating pollen and raised for the beneficial effects of supplemental pollen. The protocols for collecting information required to rate seedlots vary by species and location, but the calculations for estimating genetic worth, pollen contamination and genetic diversity are the same. Both the protocols and the formulae used to calculate the genetic quality of orchard seed lots are discussed.
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