Nondestructive estimation of anthocyanin content in grapevine leaves

The anthocyanin (Anth) content in leaves provides valuable information about the physiological status of plants. Thus, there is a need for accurate, efficient, practical methodologies to estimate this biochemical parameter. Reflectance measurement is a means of quickly and nondestructively assessing leaf Anth content in situ. The objective of this study was to test the overall performance and accuracy of nondestructive techniques for estimating Anth content in grapevine leaves. Relationships were established between Anth content and four vegetation indices: NIR (near-infrared)/green, red/green, anthocyanin reflectance index (AR1, based on reflectances in bands within the green and the red-edge regions), and a modified anthocyanin reflectance index (MARI, based on reflectances in green, red edge, and NIR). The algorithms for Anth retrieval were calibrated. The accuracy of Anth prediction was evaluated using an independent data set containing sampled leaves from two field-grown grape cultivars (Saint Croix and Saint Pepin) with no adjustment of the coefficients after initial calibration. Although Anth in the validation data set was widely variable, from 3 to 45 nmol cm ², the ARI and MARI algorithms were capable of accurately predicting Anth content in grapevine leaves with a root mean square error below 3 nmol cm ² and 2.3 nmol cm ², respectively. Such an approach has potential for developing simple hand-held field instrumentation for accurate nondestructive Anth estimation and for analyzing digital airborne or satellite imagery to assist in making informed decisions regarding vineyard management.