LOW-LEVELS OF OUTCROSSING IN PINUS-LEUCODERMIS - FURTHER EVIDENCE IN ARTIFICIAL STANDS

Outcrossing rates were estimated in two artificial stands of Pinus leu codermis, a wind pollinated conifer characterized by a relatively high level of selfing. Multilocus outcrossing rates, estimated by assaying five enzyme loci, were lower than 86% in the two stands, using both d ormant and germinating seeds, and not different from those observed in two natural populations located in the same area. The lack of relevan t differences between single-locus minimum variance means and the mult ilocus outcrossing rate estimates observed in both the artificial stan ds indicates that most of the apparent selfing is probably caused by a ctual self-fertilization. The presence of a high level of self-fertili zation in this species seems confirmed also in artificial stands, wher e the density is higher and neighbourhood structure should be less pro nounced. The high level of self-fertilization found in P. leucodermis, which is probably due to the presence of a reduced number of recessiv e embryonic lethals as a consequence of genetic drift, could represent a selective advantage for this pioneering and precocius species.