SELECTION AGAINST INBREDS IN EARLY LIFE-CYCLE PHASES IN PINUS-LEUCODERMIS ANT

Conifers are self-compatible hermaphroditic plants which usually show very low levels of selfing and severe inbreeding depression. Positive fixation indices are observed in the seed stage owing to partial selfi ng but not in the adult stage and selection against inbreds has been f requently invoked to explain this observation. To determine the stage of elimination of inbreds in Pinus leucodermis Ant., a narrow-ranged a nd relic species characterized by 18-28 per cent selfing rates, fixati on indices at isozyme gene loci were estimated in nursery grown indivi duals at three different juvenile life-cycle phases and in adult paren t trees. Two populations with different levels of selfing were studied . In both populations a deficiency of heterozygotes as a result of sel fing was observed in dormant and in germinated embryos, while an exces s of heterozygotes comparable with that of the adult trees was found i n 5-year-old plantlets. Young plantlets of the same two populations gr own in the wild also had negative fixation indices confirming that sel ection takes place in the first years of growth.