Abstract

In order to test the sensitivity of colorimetric technique in phytodiagnostics, with particular regard to color variations caused by water stress, and to verify the potential for use in irrigation timing of horticultural crops, water stress was induced on two-year-old, container-grown Citrus macrophylla and 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 aim of evaluating the accuracy of the instruments and to point out possible drift effects due to prolonged use. The trend of colorimetric and xylematic pressure potential values over time were measured on 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)/z 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.

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