Pollen contamination in a maritime pine polycross seed orchard and certification of improved seeds using chloroplast microsatellites

A new concept of seed orchard was developed by Institut National de la Rech erche Agronomique for the maritime pine (Pinus pinaster Ait.) breeding prog ram: the polycross seed orchard (PSO). The expected genetic gain of the PSO can only be reached if the fathers used in the pollen mix contribute equal ly to the next generation (i.e., to the base material of the PSO) and if po llen contamination from the surrounding stands is limited. Using chloroplas t simple-sequence repeats (cpSSR), we showed that the chloroplast DNA was u nipaternally inherited in maritime pine and verified that the chloroplast h aplotype composition of the megagametophyte tissue corresponded to the chlo roplast haplotype of the female parent. As a practical application, a stati stical test based on cpSSR markers and simulation was established to verify the PSO origin of maritime pine seed lots. As a result of the cpSSR test, it was observed that (i) departure from even distribution of the fathers in the PSO was barely significant, (ii) the minimum pollen contamination rate in the PSO was 36%, and (iii) the contamination was not evenly distributed in the PSO. As a consequence, the expected genetic gain will range between 50 and 82% of what was initially foreseen.