Annasamy Chandrakala, Barrett Rock, and Rebecca Sideman, Marta Lima*
*University of New Hampshire – Agriculture, Nutrition, and Food Systems/Virginia Tech – School of Plant and Environmental Sciences, Saunders Hall , 490 W Campus Dr, Blacksburg, VA, 24061, USA (martalima@vt.edu)

Training systems influence the microclimate of grapevines in the vineyard, which can affect overall plant health and productivity. Spectral data obtained through remote sensing techniques can provide information regarding plant health. In 2019, we conducted a study in an experimental vineyard at the University of New Hampshire (Woodman Research Farm, Durham, NH) to compare the leaf spectral signatures of grapevines growing on two different training systems, vertical shoot-positioning and Munson. Two cold-hardy seedless table grape varieties, Canadice and Mars, were followed throughout the growing season. Leaf samples were collected weekly, from flowering to harvest, to generate hyperspectral curves using an analytical spectral device. The spectral data were used to calculate the following indices: Normalized difference vegetation index (NDVI), red edge inflection point (REIP), and moisture stress index (MSI). The same leaf samples were used to determine pigment content (chlorophyll a, chlorophyll b, and carotenoids). The vegetative indices NDVI and REIP correlated strongly with leaf chlorophyll a and b contents in both varieties. Concen­trations of chlorophyll and carotenoids can vary when plants respond to stress, and sometimes additional pigments can build up within the leaves. These variations can appear as subtle spectral changes in the visible and red-edge regions of the spectral curves. We found decreased chlorophylls, which correlated well with the vegeta­tive indices values and is likely related to reduced net photosynthesis and growth responses when grapevines were approaching the end of the growing season. The indices and pigment content of the grapevine leaves varied significantly across time (from start to end of the growing season), but were not significantly different among the two training systems.

Funding Support: This work was supported by the USDA National Institute of Food and Agriculture, Hatch project 1020314