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Exotic eucalypt hybrids go undercover

Robert Barbour
Forest Geneticist
University of Tasmania

Ben Gosney and Robert Barbour stand next to a Eucalyptus ovata x E. nitens exotic F1 hybrid that has reached the adult foliage stage of development. Morphological analyses and visual assessments of these older hybrids found them very difficult to distinguish from their pure E. ovata half-sibs.

Pollen dispersal from eucalypt plantations into native forest represents one area of research being conducted by the CRC for Forestry. This process is facilitated by hybridisation between plantation and adjacent native populations, allowing for the establishment of exotic hybrid seedlings. From the early stages of this research program, the Tasmanian native species Eucalyptus ovata was identified as being at potential risk of genetic contamination. This was based on the fact that hybrids involving plantation-grown E. nitens were not only being found among open-pollinated seed lots grown in the glasshouse, but also as seedlings at a number of sites around the island of Tasmania. These findings stimulated the establishment of a set of field trials in the Meander Valley, which have provided valuable insight into the performance of the exotic hybrids relative to the locally adapted pure E. ovata (see related article). However, one recent and quite unexpected finding by Ben Gosney and Robert Barbour (pictured, left) has emerged from these trials.

Considerable analysis of the morphological characteristics of the exotic E. ovata hybrids as juvenile seedlings has ­
­adult hybrid - bob barbour

This discriminant analysis plot summarises the morphological differences in adult Eucalyptus amygdalina, E. viminalis, E. nitens, E. ovata and E. ovata x E. nitens F1 hybrids growing in the Meander Valley trial, Tasmania. The hybrids (solid symbols) were found to be very difficult to distinguish from their E. ovata half-sibs based on morphological traits.

demonstrated that they are typically easily distinguishable by eye from the pure E. ovata. In the Meander field trials, that have now reached seven years of age, many of the hybrids have undergone developmental “phase change” from juvenile to adult morphology.  This transformation of leaf morphology is extremely distinct in many eucalypt species, including E. nitens and many of its hybrids. In the adult phase, the hybrids within the trials have been found to be difficult to distinguish from the pure E. ovata. This will make identification and management of these exotic mature hybrids very difficult for forest managers. Consequently, the early detection of this potential risk of genetic incursion, and the establishment of the Meander field trials, has given the research team a “heads up” on the potential problems associated with managing exotic hybrids. The exotic hybrids that have established in the wild to date are not expected to have reached the adult foliage phase (see related article).  These findings also highlight the importance of establishing field trials with other hybrid combinations involving E. nitens, described in a related article.