Realised genetic gains and estimated genetic parameters of two <i>Eucalyptus grandis</i> × <i>E. urophylla</i> hybrid breeding strategies

Abstract

Conventionally, Eucalyptus grandis × E. urophylla (GU) hybrid material is first tested as seedlings in progeny trials for at least four years before ortets are selected and ramets of the selected ortets are 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 spent 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 was to do a comparative study between the CHBS and AHBS, firstly to 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 indicated that the percentage realised volume gains per year was higher for the AHBS (3.7%) than for the CHBS (1.9%) when compared with the GU commercial clone. Thus, shortening the testing time of GU seedlings had a positive impact on volume gains per year. With regard to genetic parameters, both the AHBS and CHBS clonal populations indicated that non-additive genetic variation explained the 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 spent 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.

Keywords: Eucalyptus grandis × E. urophylla clonal populations, genetic parameters, hybrid breeding strategies, realised genetic gains