VR O43-43
| Variety Passport | |
| Country of origin: | USA |
| Breeder: | University of California, Davis |
| Variety number VIVC: | 17307 |
| Prime name: | Olmo VR O 43-43 |
| Breeding number: | VR O43-43 |
| Patent: | Plant 6,319, USA |
| Principal Synonyms: | VR O43-43, O 43-43, O43-43 |
| Year of obtaining / registration: | The cross was made in 1948, and the patent was issued on October 4, 1988. |
| Pedigree given by breeder: | Hunisa × Vitis Rotundifolia male No. 2 |
| Pedigree confirmed by markers: | Hunisa × Vitis Rotundifolia male No. 2 |
| Rootstock type: | Nematode-resistant |
| Data Sources: | Vitis International Variety Catalogue (VIVC), University of California, Davis (UC Davis), Google Patents |
| Agrobiology | |
| Flower type: | male |
| Nematode susceptibility: | 1 point (highly resistant) |
| Root phylloxera susceptibility: | 3 points (low resistance) |
| Rooting ability: | low |
| Graft compatibility with Vitis vinifera: | high |
| Ampelographic overview |
History of Origin and Agricultural Importance
The grapevine rootstock variety VR O43-43 was developed by American viticulturists Lloyd A. Lider, Harold P. Olmo, and Austin C. Goheen at the University of California, Davis. The parental cross was performed in 1948. Although the initial results demonstrating its phylloxera resistance were published in 1964, the selection was not immediately released for commercial production due to difficulties encountered in its vegetative propagation by cuttings. The patent for this grapevine rootstock was officially issued on October 4, 1988.
The primary agricultural value of the hybrid lies in its ability to effectively tolerate the grapevine fanleaf virus–Xiphinema index nematode complex, which causes infectious degeneration. This rootstock exhibits complete immunity to feeding by the dagger nematode (Xiphinema index), the vector responsible for spreading the fanleaf virus. Field trials conducted in the premier wine grape regions of Napa and San Joaquin counties in California demonstrated that scions of susceptible Vitis vinifera cultivars grafted onto VR O43-43 and planted in nematode-infested soils remained fully productive and completely free of virus symptoms for at least 7 years of observation. In contrast, control vines on standard commercial rootstocks showed severe degeneration and a drastic decline in crop yield.
In addition to its strong immunity to Xiphinema index, the grapevine rootstock VR O43-43 shows resistance to most strains of root-knot nematodes. A key biological feature distinguishing this variety from its sibling companion rootstock VR O39-16 is its tolerance (moderate resistance) to the root form of phylloxera rather than total immunity. It exhibits excellent grafting compatibility with popular wine grape cultivars of Vitis vinifera, including Cabernet Sauvignon, Chenin Blanc, and Carignane, ensuring stable vine vigor, good annual pruning weights, and normal berry composition.
Morphological Description of the Rootstock Variety VR O43-43
Over years of observation, scientists compiled the following morphological description of the variety:
- Flowers: Distinctly staminate (male type) with long filaments. Pollen is completely non-viable. The ovary is indistinct or rudimentary. Flower clusters are small, measuring 4 to 6 cm in length, completely sterile, and do not set fruit.
- Mature Leaves: The leaf blade is green, moderately three- to five-lobed, occasionally almost entire. Both inferior and superior lateral sinuses are open and narrow. The leaf margin is dentate with a clear tendency toward an irregular arrangement of large, acute teeth. Mature leaves feature a tufted tomentum on the upper surface, while the lower surface is completely glabrous.
- Young Shoots and Apex: Growing shoot tips and young leaves are light green in color. The upper surface of young leaves is covered with moderately soft hairs, whereas the lower surface remains glabrous.
- Tendrils: Bifid, occasionally trifid, long and slender, frequently exceeding the length of the leaf blade, completely glabrous. The discontinuous arrangement of the tendrils corresponds to the Vitis vinifera type.
- Herbaceous Shoots: Immature stems feature prominent ridges and appear distinctly angled when young. The surface of the shoots has widely dispersed soft hairs. Petioles and immature wood are light green.
- Mature Wood: Mature one-year-old canes are tan in color. The bark is persistent with distinct, well-defined lenticels. A dividing septum (diaphragm) is present at the nodes.
- Phenological Features: Flowering occurs late in the season, typically 10 to 12 days later than the commercial cultivar Semillon.
Propagation and Nursery Management Practices
In practical nursery management, the VR O43-43 rootstock is recognized as a technologically challenging variety to propagate, as its cuttings root with significantly more difficulty compared to standard phylloxera-resistant rootstocks traditionally used in commercial production. To ensure successful sapling development and to stimulate root formation in the nursery bed, the application of commercial growth regulators and rooting hormones during cutting preparation is a mandatory viticultural practice.