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.
The European grapevine (Vitis vinifera L.) has been cultivated in North America for about 500 years. One of the major limitations to its culture is the powdery mildew (PM) fungus, Erysiphe necator Schw. This study reports on the most extensive screening of Vitis species from the southwestern United States and northern Mexico for resistance to PM, testing 147 accessions of 13 Vitis species. In addition, Vitis vinifera cv. Carignane, a highly susceptible wine grape cultivar, was used as a reference to evaluate the effect of the inoculum 14 days postinoculation. Inoculation was done with a vacuum-operated settling tower using a broadly virulent isolate of E. necator, the C-strain. Resistant accessions (nine), moderately susceptible accessions (39), and highly susceptible accessions (99) were detected. The resistant accessions were then inoculated with an additional fungal isolate, e1-101, and they retained their resistance. Vitis species susceptibility was not associated with a North-South gradation, but Western species were more susceptible than Midwestern and Eastern species. All five of the V. monticola accessions were susceptible, as were the accessions of V. treleasei. The species V. acerifolia, V. candicans, V. cinerea, and V. × doaniana had significantly more resistant to moderately susceptible accessions compared with V. arizonica, V. berlandieri, V. californica, V. × champinii, V. girdiana, V. riparia, and V. rupestris, which had relatively more susceptible accessions than the other species. This research identified new sources of PM resistance in Vitis from the southwestern United States that could be incorporated into PM resistance breeding programs throughout the world.
Mechanistic modeling constitutes a powerful tool to unravel complex biological phenomena. This study describes the construction of a mechanistic, dynamic model for grapevine plant growth and canopy biomass (vigor). To parametrize and validate the model, the progeny from a cross of Ramsey ( Vitis champinii ) × Riparia Gloire ( V. riparia ) was evaluated. Plants with different vigor were grown in a greenhouse during the summer of 2014 and 2015. One set of plants was grafted with Cabernet Sauvignon. Shoot growth rate (b), leaf area (LA), dry biomass, whole plant and root specific hydraulic conductance (k H and L pr ), stomatal conductance (g s ), and water potential (Ψ) were measured. Partitioning indices and specific leaf area (SLA) were calculated. The model includes an empirical fit of a purported seasonal pattern of bioactive GAs based on published seasonal evolutionary levels and reference values. The model provided a good fit of the experimental data, with R = 0.85. Simulation of single trait variations defined the individual effect of each variable on vigor determination. The model predicts, with acceptable accuracy, the vigor of a young plant through the measurement of L pr and SLA. The model also permits further understanding of the functional traits that govern vigor, and, ultimately, could be considered useful for growers, breeders and those studying climate change.
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