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Screening Eucalyptus nitens seedlings for resistance to browsing

Julianne O’Reilly-Wapstra1, Hugh Fitzgerald1, Paul Tilyard1, Dean Williams2, Tim Wardlaw2 and Brad Potts1
1School of Plant Science, University of Tasmania
2Forestry Tasmania
E-nitens-field-site

The mission: to sample all the seedlings in this plantation and keep track of which is which!

One avenue for reducing damage to forestry seedlings by browsing mammals is to plant genetic stock that has naturally high levels of plant defensive chemicals. While this ‘tool’ may not completely prevent browsing from occurring, it does reduce browsing to seedlings in operational field trials (Miller et al., 2009) and in standard operational plantations (Glancy, unpublished data). In addition, when compared to various other browsing management tools such as stockings and repellents, the effects of genetic resistance levels in seedlings were maintained over a longer time period (one year) in operational field trials. The other options were superior in the short term but their effectiveness deteriorated over time while the genetic effects continued to confer protection in the long term (Miller et al., 2009).

Julianne-Justin-Hugh

Julianne O'Reilly-Wapstra, Justin Bloomfield and Hugh Fitzgerald prepare to sample 1700 E. nitens seedlings.

Foliage from E. globulus and E. nitens contains high levels of plant secondary metabolites, such as tannins, terpenes and formylated phloroglucinol compounds (FPCs), which have been shown to consistently affect feeding by marsupial herbivores (O'Reilly-Wapstra et al., 2004; Moore and Foley, 2005; Marsh et al., 2006). Various trials have shown that the resistance level of field seedlings to mammalian browsing is correlated with some of these compounds, in particular with sideroxylonal (one of the FPCs).

It would be a great advantage for forestry companies to be able to screen their current deployment stock for levels of sideroxylonal and other defensive compounds. At UTAS we employ near-infrared reflectance spectroscopy (NIRS) as a rapid predictive tool to determine the concentration of these chemicals in eucalypt foliage samples. This tool allows us to screen large numbers of plants in a relatively short amount of time.

In a recent project we harvested foliage from 1700 E. nitens seedlings from two sister family trials on contrasting sites in southern Tasmania. The seedlings included current deployment stock. We recently finished scanning the foliage using NIRS and the defensive chemical profiles of the 1700 seedlings are currently being predicted. This information will allow deployment stock to be ranked for resistance to browsing by mammalian herbivores which, in turn, will help industry to make decisions about how to deploy their seedling stock to best effect.

Marsh, K. J., Wallis, I. R., McLean, S. et al. (2006). Conflicting demands on detoxification pathways influence how common brushtail possums choose their diets. Ecology, 87, 2103-2112.
Miller, A. M., O'Reilly-Wapstra, J. M., Potts, B. M. et al. (2009). Non-lethal strategies to reduce browse damage in eucalypt plantations. Forest Ecology and Management, 259, 45-55. [read]
Moore, B. D. and Foley, W. (2005). Tree use by koalas in a chemically complex landscape. Nature, 435, 488-490.
O'Reilly-Wapstra, J. M., McArthur, C. and Potts, B. M. (2004). Linking plant genotype, plant defensive chemistry and mammal browsing in a Eucalyptus species. Functional Ecology, 18, 677-684. [read]



Biobuzz issue thirteen, December 2010