Seed Orchards and Aspects on Supporting Tree Breeding

Abstract

The main quantitative output and work horse for plant breeding today and accumulated efforts since half a century is seed orchards. This document do not cover deployment of vegetatively propagated material or control crosses (less than 2 % of number of Swedish forest plants produced) or GMO or genomic based selections (zero plant production) and focus mainly on Sweden. Seed orchards established now are mainly with tested grafted clones. With Norway spruce, where vegetative propagation of young plants is easy, current testing and seed orchard deployment is based on testing clonal performance. For Scots pine it is progeny tested clones, but progeny testing is a painfully slow and seemingly inefficient procedure. The number of clones is typically 20 or slightly more when clones are unrelated. It is more efficient to deploy clones in different proportions and it is not economic to strive for equal proportions. Pollen contamination is an important aspect of seed orchards, a practical remedy has not been found. However, seed orchard crops from genetically young seed orchards with 100 % contamination are still better than crops from mature but genetically outdated alternatives. Earlier deployed clones were unrelated, but it seems to become inefficient avoiding related clones after the first generations. Genetic thinning is rare and difficult to defend from a gain point of view, but selective harvesting becomes increasingly common. The breeding population (typically 1,000) is shared in compartments (typically 50) and seed orchards draw on several compartments. Probably both seed orchards and breeding would benefit from a larger “breeding population”. There would be advantages if breeding efforts and seed orchard establishment could be better synchronized. New cohorts of recently selected clones should be deployed to pine seed orchards more often, they tend to be genetically worn out and expensive to harvest. Projections of the impact of seed orchards on the national forest harvest almost a century ahead in Sweden is 10 % assuming no technology change. The possible “ecological risks” with the seed orchard technology seem a small addition to that of plantation forestry.