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Orchard populations are artificial and intensively managed populations of elite, best-performing trees that are established for mass production of genetically improved seeds. Seed orchards connect cycles of selection, breeding, and testing of plus-trees with the deployment of the improved seeds at the operational plantations. Long reproductive cycles and rotation age, irregular flowering of trees pose serious threats to the economic success of tree breeding and urge efficiency monitoring. This thesis describes genetic functioning of Swedish seed orchard of Scots pine and Norway spruce, diversity levels of orchard crops, their performance in the field in connection with their genetic background, and possible ways to stimulate flowering. It is especially relevant now when molecular technologies became more affordable and allow more intensive sampling and genome coverage.

We detected differences between the two species in all genetic parameters and higher diversity levels in Scots pine crops. Crop diversity was at acceptable level though slightly reduced compared to reference population. We detected great variation in flowering in orchard parents, and the influence of linear deployment strategy on diversity, reproductive success, and effective number of orchard parents. Frost tolerance of a crop depended on the origin of orchard parents but up to a smaller extent than was previously expected.

Seedlings orchard crops perform well in the field, and do not suffer from increased mortality while their counterparts from controlled crosses have variable performance and tend to form G-by-E interactions. Overall, selected seed sources perform better than forest seed lots, and this superiority is independent from the silvicultural methods at the between-sites level. Site preparation methods and planting positions play a larger role at each location and may enhance survival and growth. Seed weight correlates positively with height, while diameter is more affected by the planting position.

Topgrafting showed varying degree of success but efficiently reduced time to flowering to 1 year after the grafting procedure. The extent of male and female flowering was dramatically different, and for satisfactory cone crops, there is a great need in the application of flowering stimulation methods.

This is a first systematic attempt to analyse genetic background of mating and population structure of several crops from different orchards of the two species. It describes the success of Swedish tree breeding strategy in conserving genetic diversity, improving survival and economic traits, and provides the assessment of linear deployment strategy with the advanced molecular techniques. We emphasize the urgent need to efficiently stimulate flowering in both species for securing orchard production and balanced genetic composition.