Physiological and genetic control of vigour in a 'Ramsey' × 'Riparia Gloire de Montpellier' population

Vigour control in grapevine can be achieved by grafting with particular rootstocks, and may become especially important under climate change. This research studied the F₁ progeny from the cross of 'Ramsey' × 'Riparia Gloire de Montpellier' rootstocks, known to confer high and low vigour, respectively. We hypothesized that vigour correlates with growth rate, leaf area, biomass partitioning, plant hydraulics and gas exchange; and that these variables could be associated with genetic markers. We evaluated 138 seedlings from this cross, three replicates each, for 60 days in a greenhouse at UC Davis, California, during summer 2014 and 2015. Each plant was pruned to a single shoot and watered daily. Shoot growth rate, leaf area and dry biomass were measured for the complete population, both years. In 2014, after day 45, 40 genotypes were subjected to a 50% water deficit, based from initial weight at full pot capacity, and plant and root hydraulic conductance's, stomatal conductance and water potential were measured. The progeny showed transgressive segregation and significant differences in vigour. A PCA analysis showed a strong role for shoot growth rate, specific leaf area, plant hydraulics and partitioning indices for vigour determination. Under water stress, larger plants showed less specific hydraulic and stomatal conductance's, indicating higher sensibility upon drought. Significant QTLs for leaf area, specific leaf area and partitioning indices were found on chromosomes 1, 4, 16, and 5; accounting for 20% of explained variability for leaf area, and from 10 to 14% of explained variability for specific leaf area and partitioning indices in 2014. Mapping data from 2015 is being analysed.