Colorimetric Technique for Evaluating Leaf Stress Status : An Example for Water Stress.

Abstract

In order to test the sensitivity of colorimetric technique in phytodiagnostics, with particular regard to color variations caused by water stress, an d to verify the potential for use in irrigation timing of horticultural crops, water stress was induced o n two-year-old, container-grown Citrus macrophylla an d Citrus paradisi cv. Star Ruby plants in the third year after grafting. Measurements on plant leaves were preceded by a test of the colorimeter with the ai m of evaluating the accuracy of the instruments an d to poi n t out possible drift effects due to prolonged use. The trend of colorimetric an d xylematic pressure potential values over ti me w ere measured o n leaf samples. Color of well-watered plant leaves showed very small variations while unwatered plant leaves presented a wide change in color. In addition water stress determined an increase in both the dominant wavelength and the saturation. The chromaticity co-ordinates y and z and the index (x+y)lz showed the best sensitivity in discriminating color variations. Moreover, clear correlations between xylematic pressure potential and chromaticity co-ordinates were found. Use of colorimetric technique may improve the possibilities for irrigation management, with particular regards to irrigation timing.