2 METHODS FOR THE ANALYSIS OF COLORIMETRIC COMPONENTS APPLIED TO PLANT STRESS MONITORING

Several authors have shown the possibility of early detection of many stress conditions in plants by analysing leaf colour. The availability of portable instruments, increasingly accurate and reliable, leads to the belief that, in the near future, this technique could be used for routine analysis in the field. Nevertheless, due to the variability o f the leaf colour parameter and consequently to the large amount of da ta to be collected to obtain a representative sample, direct analysis of chromaticity coordinate values, as generated by an instrument, coul d give results that are hard to interpret, especially when the colour variation to be detected is subtle, such as in leaves at the first sta ges of stress. The availability of standard methodologies to analyse c olorimetric data would allow them to be interpreted correctly and, in a short time, to widen their fields of application. In this work two m ethods of elaboration, with related software (PCA and COLORE) that giv e an objective evaluation of colorimetric variations of stressed plant s by means of specific indexes of alteration, are illustrated. PCA, ba sed on principal components analysis, allows two 'indexes', T-ij and D , to be calculated, that can describe the differences between two or m ore treatments. It also allows the location of the different treatment s on the chromaticity diagram to be graphically represented. COLORE ca lculates the values of the dominant wavelength and purity of the colou r. From these, it computes the CI index that can be related to degree of stress. The two softwares were applied to data from different studi es of thermal and water stress in Sorghum bicolor ((L.) Moench) and Ci trus macrophylla (L). The results showed a clear correlation between t he colorimetric indexes and the ecophysiological parameters chosen as indicators of stress. (C) 1998 Elsevier Science B.V.