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Pollen contamination is a serious problem in seed orchards, which may reduce genetic gain considerably. High levels of pollen contamination can be reached even when the stands are isolated by several hundred of meters from natural populations. Recently, molecular markers have been used to trace details of reproductive processes. The efficiency and utility of estimating mating system, gene flow and pollen contamination are greatly increased by using microsatellite markers, which are ideal for parentage studies and fingerprinting, due to their high discrimination power. The aim of the present study was to estimate the pollen contamination in a clonal seed orchard (CSO). Three nuclear microsatellites were used to screen the 60 different clones from the CSO and the 206 seeds collected from 7 trees from each one of the three plots distributed according to the main winds direction. The 3 loci distinguished the 60 clones genotypes, but 2 pairs. Minimum and maximum estimates of pollen contamination were 46% and 56%, respectively. Those values could be explained by the presence of a P. pinaster stand at a distance lower than 2 Km and the existence of natural regeneration of this species on the orchard’s isolation zone. External plots pollen contamination was higher than in the inner plot. Only 20% of the clones contributed for the next generation, which may lead to a reduction of seeds’ genetic variability. However, an asymmetrical sampling from the orchard (3 plots) was made, which might have biased the results, and the effective number of clones participating in the next generation might be higher. The outcross pollination rate was found to be very high - 90.2%. The minimum estimate of biparental inbreeding was 21.2%, a not so high value if we consider the number of seeds sampled and the orchard size.

The original publication is available at/A publicação original encntra-se disponível em: www.afs-journal.org