The fractal spectrum of leaf colour as a tool for measuring frost hardiness in plants

An image analysis method, based on the calculation of the fractal spectrum of leaf colour, was evaluated for its potential use in assessing frost hardiness in plants. The technique developed consisted of a) digitization of the leaves after freezing treatments, b) splitting of the images obtained into the three components of the RGB (red, green and blue) colour system and c) calculation of the fractal spectrum for each colour component of the leaf. It was then tested to assess the freezing hardiness of acclimated and non-acclimated Callistemon linearis plants. The analysis system consisted of a scanning device, a personal computer and the image analysis algorithm. All the fractal parameters showed a sigmoidal relationship with temperature. From the inflection point, the LT50 calculated for acclimated and non-acclimated plants, was -7.5 and -4.8°C, respectively. The LT 50 calculated from the electrolyte leakage test on the same material was about 2°C warmer than the LT50 obtained from fractal analysis. The role of fractal analysis of leaf colour as an additional, rapid and inexpensive method for identifying freezing damage is discussed.