Pollen contamination and mating structure in maritime pine (Pinus pinaster Ait.) clonal seed orchards revealed by SNP markers

Abstract

AbstractMaritime pine (Pinus pinaster Ait.) is a major forest tree species in south-western Europe. In France, an advanced breeding program for this conifer species has been underway since the early 1960s. Open-pollinated seed orchards currently supply more than 90% of maritime pine seedlings for plantation forestry. However, little is known about pollen contamination and mating structure in such seed orchards for maritime pine. We analyzed these features here, focusing on: i) the location of the seed orchard, ii) the year of pollination, and iii) the genotype of the tree from which seeds were collected. Parental analyses based on an optimized set of 60 SNP markers were performed on 2,552 seedlings with Cervus software (likelihood inference methodology).Pollen contamination rates were highly variable between seed lots (from 20 to 96%), with a mean value of 50%. Several interpretative factors were highlighted, including the distance between the seed orchard and external pollen sources, rain during the pollination period, seed orchard age, soil characteristics and seed parent identity. All parental genotypes contributed to the offspring as pollen parents, but differences in paternal reproductive success were detected. These differences were only partly explained by differences in the number of ramets of each parental genotype deployed in each seed orchard. Finally, the overall self-fertilization rate was estimated at 5.4%, with considerable variability between genotypes. These findings are useful to formulate recommendations for seed orchard management and for identifying new research perspectives.