Inbreeding Depression in the Full-sib Offspring of Populus nigra L.

Controlled pollination was carried out in the species Populus nigra L. in a greenhouse on isolated branches between sisters and a brother - inbreeding (S x B). Female trees (sisters) were also exposed to open pollination (OP) in the neighbourhood of a male tree (brother) and other Populus nigra trees in the vicinity. The analysis of 11 microsatellites was done in the offspring from the inbreeding (S x B) and from the OP. In OP offspring was found 20-76% of viable individuals that were coming from pollination with brother’s pollen (spontaneous inbreeding). These individuals were separated from the offspring. In a randomised field trial the offspring were evaluated for two years. Fitness decreased in S x B offspring, traits of plant height, trunk diameter, height increment and resistance to Melampsora larici-populina Kleb. were lower in comparison with those of OP offspring. A coefficient of inbreeding depression (δ) ranged from 0.373 to 0.034. The significance of differences between the offspring from S x B and OP of the particular sisters was proved. About 30% of homozygous microsatellite loci were identified in inbred S x B offspring, which was more than in OP offspring. This difference was significant in the offspring of three sisters; it was not significant in the offspring of one sister. This trend corresponded to the results of growth traits.