This study describes the construction of a theoretical model for plant vigor. The model conceives vigor as the result of the interaction of external environmental stimuli, mainly soil and atmospheric conditions, and plant physiological behavior. Soil water status directly affects root hydraulics. Atmospheric humidity, water vapor pressure deficit, light, and temperature affect leaf water potential and stomatal conductance. These responses to external inputs influence plant gas exchange (stomatal conductance and photosynthesis), tissue turgor, and cell expansion. These factors, also influenced by hormonal signals, determine total C assimilation and biomass partitioning, affecting plant growth and vigor. To parameterize and test our model, we studied the F1 progeny from a cross between Ramsey and Riparia Gloire de Montpellier, rootstocks that confer high and low vigor, respectively. We evaluated 138 genotypes, three replicates each, for 60 days in a greenhouse at UC Davis, California, in summer 2014 and 2015. Each plant was pruned to a single shoot and watered daily. In 2014, after day 45, 50 genotypes were subjected to a 50% water deficit, based on initial weight at full capacity. Shoot growth rate, leaf area, and dry biomass were measured for the complete population (including the stressed subset), while hydraulic conductance, stomatal conductance, water potential, and chlorophyll content were measured in the 50 genotypes. In 2015, we repeated the evaluation, adding photosynthesis and root hydraulic conductance measurements in the own-rooted population and a grafted subset, using Cabernet Sauvignon as scion. We will present a preliminary model showing the main mechanisms, inputs, and outputs that control plant vigor. Future goals include completing the model, running simulations, and validation.

Funding Support: Estación Experimental Agropecuaria Mendoza, INTA