Characterization of Physiological Factors and Performance of Ungrafted GRN Rootstocks Under Moderate Water-Stress Conditions

The commercial production of grapevines (Vitis vinifera L.) relies heavily on rootstocks that are hybrids of non-vinifera parentage. The relatively newly released GRN rootstocks (GRN-1, GRN-2, GRN-3, GRN-4, and GRN-5) were bred from especially under-studied genetic backgrounds. This study aimed to evaluate ungrafted GRN-series grape rootstocks under moderate water-stress conditions and to characterize and compare their physiological performances. Each of the GRN rootstocks had specific physiological characteristics that would make them suitable for a wide range of growing conditions and vineyard management goals. GRN-1 had growth habits which were more vigorous and the highest carbohydrate storage levels, while GRN-2 had the highest level of nitrogen and the largest leaf area, but the lowest levels of carbohydrate storage. GRN-3 was less tolerant to high-salinity soils, and had the longest internodes, while GRN-4 had high boron levels, which supports flowering and fruit set, and short internodes. GRN-5 was consistently moderate across all measured areas, except internode thickness, for which it was the highest. These findings show the variations in physiological growth habits among the ungrafted GRN-series rootstocks and suggest that growth habits, carbohydrate storage, leaf canopy, fruit production, and nutrition vary based on rootstock parentage. Further investigation is needed to determine whether these characteristics persist when grafted onto Vitis vinifera L. scions.