Post-pollination capsule development in Eucalyptus globulus seed orchards

Low capsule set is a major factor limiting seed production in Eucalyptus globulus seed orchards. Trials were conducted in E. globulus seed orchards in Tasmania, Australia, to identify the timing of capsule development and abortion, as well as the influence of pollination type, the number of ovules fertilised and weather events on capsule set. Controlled pollination (CP), mass supplementary pollination (MSP), open pollination (OP) and isolated unpollinated control (UP) treatments were performed on 21 genotypes in an orchard in southern Tasmania in 2004-2005 and on six genotypes in a higher-altitude orchard in north-western Tasmania in 2005-2006. No capsules were set in the UP control treatment, and capsule set was significantly lower following CP than OP and MSP. The major period of capsule abortion occurred between 20 and 80 days after pollination for all pollination methods across both sites, coinciding with the period of capsule growth. A positive correlation between the number of fertilised ovules per aborted capsule and the length of time capsules were held on the tree was recorded. Given that capsule abortion occurred during a period of fruit growth and that capsules with the lowest number of fertilised ovules aborted first, it is argued that fertilisation level and the level of resource competition are major factors determining capsule abortion.