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NIRS aids rapid hybrid identification

john humphries

Jon Humphreys has been developing a NIRS-based "hybrid index" as part of his PhD studies.

­ john phazir

The hand-held spectrometer that will allow large scale field-based assessments. The use of a common technology is a key driver of many cross program linkages within the CRC.  This is seen with the use of NIR. The hand-held scanner was brought initially by Research Programme Two (RP2) for assessing wood properties, but clearly has numerous applications relevant to the Biodiversity project. The interaction with Geoff Downes (CSIRO/RP2) has been of great benefit to Jon.

­Jon Humphreys
PhD student
University of Tasmania

Identification of plant hybrids produced from closely related species can be difficult using only morphological characteristics (e.g. leaf colour/shape), especially when identifying young seedlings.  Other methods such as chemical analysis can be used for this purpose, but they tend to be slow and expensive, making them unsuitable for large-scale analysis.  In our study, we wanted to see whether near infrared reflect spectroscopy (NIRS) could be used as a rapid and accurate alternative to chemical analysis for hybrid identification.  For NIRS analysis a spectrometer is used to irradiate samples with near infrared light.  The chemical bonds that make up the sample influence how much light is absorbed at different wavelengths. A spectrum is produced, which contains a large amount of information about the chemistry of the sample, which can be analysed using special software. We developed and compared calibration models developed using (a) NIRS spectra and (b) levels of essential oils obtained using wet chemical analysis, to discriminate between leaves of Eucalyptus globulus, E. nitens and their first-generation (F1) hybrids.

Models developed using both approaches could accurately identify hybrids from the pure species, however, NIRS models were slightly more accurate (>95% accuracy) and much faster than those developed using essential oil quantities, making NIRS an ideal method for hybrid identification on a large scale.

This research has now been extended to include the development of a "hybrid index" of the degree of genetic similarity between first (F1) and advanced (F2, backcross) generation hybrids and parental species.  This has been achieved using a newly acquired portable, hand-held spectrometer.  It takes less than 1 minute to scan a leaf, which means that the spectral profiles of large numbers of trees could, potentially, be determined in the field in a single day.

This research has been accepted for publication and is currently in press:

Humphreys, JR, O’Reilly-Wapstra JM, Harbard JL, Davies NW, Griffin AR, Jordan GJ and Potts BM (2008) Discrimination between Eucalyptus globulus, E. nitens and their F1 hybrid using near-infrared reflectance spectroscopy. Silvae Genetica (in press, 21/7/2008)

Biobuzz issue seven, November 2008
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