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Fitness tests for exotic hybrids

Fitness test results

Results from a set of field trials established in 2001 in the Meander Valley, aimed at testing the performance of E. ovata x E. nitens F1 hybrids. In all cases, the local E. ovata (black diamonds) can be seen to out-perform the hybrids (open diamonds) and E. nitens (triangle trial only, open triangles) (see Barbour et al. 2006 for more details). After seven years, however, many hybrids are still alive in these trials. (Image: B. Barbour)

Robert Barbour
Forest Geneticist
University of Tasmania

One potential impact of the large area of eucalypt plantations being established across Australia is the movement of plantation pollen into native eucalypt populations, resulting in hybridisation and introgression of non-local genes. This risk is being assessed through a multifaceted research project headed by Robert Barbour and Brad Potts. An important component of this research program has recently been completed, which has been focussing on the dominant plantation species in Tasmania, E. nitens.  This program involved testing the success of E. nitens as a pollen parent on all potentially cross-compatible native eucalypts in Tasmania. The end result of this work has been the production of a large number of exotic hybrid combinations. As well as being used for extensive characterisation of all potential hybrid combinations, these plants have been planted recently into four field trials in order to test their performance in the wild. The trials have been established in the habitat of the maternal seed trees from which they originated, representing the environment in which they would have to establish and grow if invasion through plantation pollen dispersal occurred. The four trials established focussed on E. ovata (n = 194 plants), E. viminalis and E. brookeriana (n = 122), E. morrisbyi (n = 68) and E. gunnii (n = 124), and have been established as transects of paired plots consisting of a hybrid and its pure species half-sib. 

Planting the trial at Lake Leake, Tasmania.

A general arboretum is also planned for every hybrid combination produced and this will be established in early spring, 2009. This research step represents an important component of the risk assessment process, as many native eucalypt species exist in harsh or unique environments relative to E. nitens. In such cases exotic hybrids are expected to perform at a lower level due to their lack of local adaptation. This has been shown to be the case in a previously established trial of E. ovata x E. nitens hybrids in the Meander Valley, in which the local E. ovata are currently out-performing the hybrids in growth, health and survival (see Figure). The more recently established trials will, therefore, provide further information on how generalised this trend is, and whether poor performance prevents hybrids from reaching reproductive maturity. It is important to note that in the Meander study, however, many hybrids have survived after seven years. Further monitoring, therefore, will be necessary to determine whether they reach reproductive maturity and allow the introgression of the exotic genes.