Stability of Outcrossing Rates in Eucalyptus globulus Seedlots

Eucalyptus globulus has a mixed mating system and selfing leads to severe inbreeding depression. Thus, outcrossing rate is an important measure of seed quality in this species. Outcrossing rates were estimated on the frequency of a rare recessive chlorophyll deficient mutant in open pollinated seed. Variation of outcrossing rates across different flowering seasons, seed sizes and storage times was assessed in E. globulus seedlots. Although there was a significant difference between the trees studied, outcrossing rates within a tree were found to be stable across four flowering seasons and three seed sizes. Storage either on the tree or in the laboratory did not alter the outcrossing rate in a consistent manner. The stability of outcrossing rates with season of pollination, age and size of seed is noteworthy as these factors may vary widely in multi-tree seedlots used for plantation establishment.