Colorado

Origin and Economic Significance

Under the name Colorado, a group of rootstock forms is understood, which were obtained in France in 1879–1880 by researchers A. Millardet and de Grasset. The breeding work was carried out using seed material of Vitis riparia collected in the state of Colorado and sent to them by E. Engelmann. The declared origin of this group was described as a hybrid combination of Riparia and Monticola*, as indicated by the characteristic glossy luster of the leaf blade. However, this hypothesis lacked rigorous scientific proof at the time; A. Millardet himself subsequently inclined to the view that the selected Colorado rootstock variety belonged to the Riparia-Rupestris group.

Within practical viticulture, the selected clone Colorado E gained the greatest renown. During the recovery period of European vineyards following the phylloxera crisis, this grape rootstock demonstrated high vegetative vigor and good adaptability to specific soil conditions. The form was developed for use on dry, stony sites and showed satisfactory results when grown on limestone Jurassic marls (under the chalky soil conditions of the Charente region).

Possessing the ability to tolerate higher concentrations of active lime in the soil compared to standard Riparia-Rupestris hybrids, the Colorado rootstock could have occupied a substantial niche in commercial production. Nonetheless, its widespread distribution was hindered by the emergence of superior hybrids involving Vitis berlandieri, which surpassed it in key adaptive and economic parameters. In modern viticulture, the Colorado rootstock variety has lost its commercial significance and retains purely botanical interest.

Morphological Description of the Colorado Rootstock Variety

• Vine: Characterized by medium vigor, with a semi-erect growth habit. The trunk forms quite thick, and the bark detaches in longitudinal wide strips of a brownish-grey shade.
• Shoots: Straight, moderately thin, internodes have an intense chestnut-red color with a distinct luster and faint longitudinal striations (ribbing).
• Leaves: Medium-sized, practically isodiametric (length almost equal to width). The blade is deeply cut, three- or five-lobed. The lateral sinuses are wide, open, and lyre-shaped. The petiolar sinus is deep, with an open V-shaped clearance. The terminal lobe, as well as the upper lateral lobes, have a distinct lanceolate shape, are elongated, and narrow visibly toward the apex.
• Leaf blade: Thick, with a parchment-like texture. The upper surface is smooth, light green, and intensely shiny. The lower surface has a paler, yellowish-green hue with a characteristic glossy luster. The main veins are slightly colored with an anthocyanin (wine) tint at their base. Numerous short hairs are concentrated along the veins on the lower side of the leaf. The marginal teeth are large, unequal, with clearly defined borders.
• Petiole: Short, relatively thick, provided with a well-defined longitudinal groove.
• Flower type: Functionally female.

Cultural Characteristics in Nursery Management

Due to the lack of widespread commercial implementation and the displacement of the form by Berlandieri hybrids, detailed technological standards for mother vine nurseries have not been established. This Colorado rootstock variety is recommended to be viewed as collection material. If propagation is required, it should be noted that the Colorado grape rootstock is adapted to stony skeletal soils with an elevated carbonate content, where it maintains stable moderate growth but is inferior to modern commercial rootstocks across the complex of traits.

*Vineyard Note: The Riparia × Monticola origin has been confirmed by DNA analysis results.