Intrinsic properties of grapevines like root system architecture are better selection criteria for developing drought-resistant rootstocks than specific physiological responses to water stress. Components of root system architecture, including rooting angle, the degree and density of branching, coarse-to-fine root ratio, and root thickness, affect the distribution of roots in the soil profile and influence root growth, seasonal development, resource acquisition and allocation, and responses to environmental conditions. Drought-sensitive commercial rootstocks possess highly branched, fibrous root systems, while drought-resistant rootstocks produce thicker roots with few lateral branches. We developed an F₁ population derived from a cross between the grape rootstocks 101-14Mgt x 110R that segregates for root system architecture based on a screen of five-week-old plants grown from herbaceous cuttings in sand in the greenhouse. To normalize the variation inherent to root measurements, root systems were characterized using two primary parameters: specific root length (root length・biomass^-1) and skewness, which assigns a value to the root diameter distribution in whole-root systems. Positive skewness indicates that the majority of roots within a root system possess diameters thinner than the average diameter, while negative skewness indicates abundant thick roots. We used a subset of F₁ progeny to validate the results of root architecture evaluations performed using the greenhouse screen with one-year-old dormant woody cuttings grown in the field in a Reiff fine sandy loam. Rapid greenhouse screens to evaluate root system architecture can aid in determining the genetic constitution of root traits and in selecting desirable architectural types for breeding complex traits like drought resistance.

Funding Support: California Grape Rootstock Improvement Commission, the California Grape Rootstock Research Foundation, the American Vineyard Foundation, the CDFA Improvement Advisory Board, the California Table Grape Commission, and the Louise Rossi Endowed Chair in Viticulture, and support for Jacob from the David E. Gallo Award, the Horace O. Lanza Scholarship, and the ASEV Michael Vail Scholarship