Stand density influences outcrossing rate and growth of open-pollinated families of Eucalyptus globulus

Using isozymes markers, we test BORRALHO and POTTS' (1996) hypothesis that poorer growth of open pollinated (OP) families of Eucalyptus globulus grown from seed-collected from less dense stands is a consequence of lower outcrossing rates. A significant relationship between stand density class and out-crossing rate was found, with outcrossing rates near one for families from closed forests. In support of BORRALHO and POTTS' (1996) hypothesis, lower parental breeding values were generally associated with lower outcrossing rates. This is no doubt due to a higher proportion of less vigorous selfs within an OP family depressing mean growth relative to families where inbred progeny were virtually absent. It is suggested that the precision of predicting breeding values with OP progenies may be improved by adjusting family performance for individual outcrossing rate.