Conventionally, Eucalyptus grandis x E. urophylla (GU) hybrid material has first been tested as seedlings in progeny trials for at least four years before ortets were selected and ramets of the selected ortets were propagated to test in clonal trials. The primary constraint with this “conventional hybrid breeding strategy” (CHBS) is the time required to first test the hybrid material as seedlings. In order to address this, an “accelerated hybrid breeding strategy” (AHBS) was investigated to reduce the time spend on testing GU hybrid material as seedlings. However, it is of utmost importance to quantify the impact the AHBS might have on genetic gains and genetic information. With this in mind, two clonal populations have been established with genetic material that derived from the CHBS and the AHBS. The main purpose of this study is therefore to do a comparative study between the CHBS and AHBS to firstly quantify the genetic gains per unit time for GU hybrid clonal populations that have been derived from the CHBS and AHBS respectively; and secondly to obtain genetic parameters such as heritabilities, the ratio of dominance, clonal within family variance and the proportion of additive and non-additive genetic variance.
The results of our study indicated that the percentage realised volume gains per year was higher for the AHBS (3.7%) than for the CHBS (1.9%) when compared to the GU commercial clone. Thus, shortening the testing time of GU seedlings had a positive impact on volume gains per year. With regards to genetic parameters, both the AHBS and CHBS clonal populations indicated that non-additive genetic variation explained majority (88% and 71% respectively) of the genetic variation. Due to the pre-eminence of non-additive genetic variation, the narrow sense heritabilties for the female and male effects were negligible for both clonal populations. Overall, the majority of the non-additive genetic variation was explained by the proportion of dominance variance, and less by the clone within family effect. These results suggest that: firstly the time spend on testing GU hybrid material as seedlings should be minimised; and secondly a hybrid breeding strategy to capture non-additive genetic variation should be adopted.