Rupestris du Lot

History of Origin and Economic Significance

The grape rootstock Rupestris du Lot is a purebred form of the wild American species Vitis rupestris, selected in France during the phylloxera crisis of the second half of the XIX century. Due to its biological characteristics, this variety became enormously widespread worldwide under the synonyms Rupestris Saint-George and Metallic. In the commercial viticulture of the USSR, the rootstock Rupestris du Lot was actively utilized in southern arid regions: in the RSFSR, in the south of Ukraine, and in the republics of Transcaucasia and Central Asia. The main advantage possessed by the rootstock variety Rupestris du Lot lies in its powerfully developed root system that penetrates vertically to a great depth, which provides the bushes with excellent anchorage in the soil. The variety Rupestris du Lot is characterized by good affinitative compatibility with most European grape varieties of Vitis vinifera. Grafting onto this rootstock stimulates vigorous vegetative development of the scion; however, on excessively fertile soils, this can lead to flower shattering, delayed crop ripening, and a certain reduction in sugar accumulation in the berries.

Soil Recommendations and Resistance to Environmental Factors

By specialized research institutions, the rootstock Rupestris du Lot is strictly recommended for dry, arid, stony, and gravelly soils where other common hybrids suffer from a severe moisture deficit. The drought resistance of this rootstock is rated as high. On the contrary, the variety Rupestris du Lot absolutely does not tolerate heavy, dense, cold soils, as well as wet sites with a high water table where its deep root system rapidly rots. The resistance to lime is moderate: the grape rootstock Rupestris du Lot is capable of withstanding a total carbonate content in the soil of up to 30% and up to 14% active lime according to the Drouineau-Galet scale. When these parameters are exceeded, the grafted plants are affected by lime-induced chlorosis. The frost resistance of the root system is at a medium level—the roots of the rootstock withstand a drop in soil temperature down to minus 7–8 °C, which is inferior to the performance of varieties from the Riparia group and requires caution in northern regions with low snow cover.

Morphological Description of the Rootstock Variety Rupestris du Lot

The botanical and morphological characteristics of the variety Rupestris du Lot are very specific and allow for easy identification of the rootstock in mother vineyards:

• Young shoot (tip): The tip of the young shoot is completely open, glabrous, and of an intense wine-purple or smooth violet-red color. The opening buds feature a characteristic metallic luster.
• Mature leaf: The leaves are small, distinctly widened in width (the width of the leaf noticeably exceeds the length), kidney-shaped or widely cordate in form, and absolutely entire. The leaf blade is thick, leathery, smooth on both sides, with the margins folded upward in the shape of a funnel. The upper side is intensely green with a strong metallic luster, and the lower side is completely glabrous, without any pubescence. The main and secondary veins are colored a bright red-violet at the base and along their entire length. The petiole sinus is widely open, flat, and often features the shape of a very gentle arc.
• Teeth: Large, wide, dome-shaped or short-saw-toothed with convex sides, terminating in a noticeable stiff sharp point.
• Petiole: Short, significantly shorter than the median vein of the leaf, glabrous, and intensely colored a dark burgundy.
• Flower: Male flower type. The bushes bloom abundantly, developing numerous small branched inflorescences that completely shatter after flowering without forming any ovary.
• Annual shoot: The cane is characterized by very large vigor of the bush and a tendency toward strong branching. The annual shoot is thick, round in cross-section, with a smooth bark of an intense reddish-brown or dark chestnut color with a violet tint. The internodes are short (usually 8–10 cm). The nodes are weakly thickened, and the eyes are small, rounded, and dark-colored.

Features of Agricultural Practices in Nursery Management

The rootstock variety Rupestris du Lot possesses an extremely strong capacity for lateral shoot formation, developing a huge mass of lateral shoots. This requires colossal costs of manual labor for conducting regular lateral shoot removal and suckering in mother vineyards. The ripening of the shoots by the end of the vegetative period is good and amounts to 80–85%, with the cane forming massive, dense wood with a very hard structure. Cuttings of the variety Rupestris du Lot give a high yield of canes, possess an excellent regeneration capacity, and root in commercial nurseries with high efficiency. However, due to the increased hardness of the wood, the cuttings require mandatory preliminary soaking before grafting. The variety is practically completely resistant to the foliar (gall) form of phylloxera and to downy mildew, but shows a high susceptibility to anthracnose, which dictates the need for regular preventive treatments of the mother vineyards.