Mating patterns, genetic composition and diversity levels in two seed orchards with few clones—Impact on planting crop

Abstract

Paternity analyses using microsatellites were conducted in two conifer clonal seed orchards (CSOs). The aim was to study mating patterns and potential dysfunctions such as unbalanced male contribution, and how these factors influence genetic diversity. The effect of unequal male contribution was quantified by the status number ( N S), which reflects build up of coancestry in the seed orchard crop due to low number of clones and unequal male contribution. This approach was also used to quantify the effect of clonal differences in germination percentages on effective population sizes. Furthermore the genetic diversity of the Abies alba and Larix kaempferi CSOs was compared to other alternative seed sources via observed heterozygosity and allelic richness. Both CSOs had a low pollen contamination rate (1.4% and 2.8%). The CSO with 12 A. alba clones showed a very skewed distribution of paternal contributions, where four clones (25%) sired more than 80% of the offspring, resulting in a status number of ( N S) = 4.6. The CSO with 10 L. kaempferi clones showed a much more equal distribution of paternal contributions, with ( N S) = 10.2. For both CSOs the paternal contributions varied significantly with sampling site within the seed orchards. The amount of selfing in the CSO seed crops was 4.7% in A. alba and 3.1% in L. kaempferi and selection against selfing could be observed. The relative self-fertility was estimated to 59% in A. alba and 33% in L. kaempferi. A study of early versus late germinating seedlings in two L. kaempferi clones indicated no increased proportion of selfed individuals in late germinating individuals. Clonal differences in germination percentages in the two CSOs had little impact on effective population sizes. The level of heterozygosity was not significantly different between CSOs and the alternative seed sources. Fixation indices ( F is) were significantly negative in the seed crops from both CSOs, indicating heterozygote excess. There were substantial differences in allelic richness between CSO seed crops and alternative seed sources. The number of alleles was 57% higher in the alternative A. alba seed source Mt. Gariglione and 25% higher in the alternative L. kaempferi seed source F410 Frøslev.