UCD GRN 3

Origin History and Economic Importance

The grapevine rootstock UCD GRN 3 was developed as part of a comprehensive breeding program initiated in 1990 at the University of California, Davis (UC Davis) by breeder Andrew Walker. The parental cross was performed in 1993–1994, and large-scale field evaluation of the progeny for nematode resistance began in 1996. The primary economic importance of this grapevine rootstock lies in providing reliable protection for the root system against a broad array of soil-borne pests. The rootstock variety UCD GRN 3 is recommended for establishing vineyards on sites with severe and chronic infestations of nematodes and grape phylloxera. It demonstrates excellent genetic stability against aggressive strains of the root-knot nematode (including HarmA and HarmC), the dagger nematode (Xiphinema index), as well as citrus and lesion nematodes. However, this rootstock is moderately susceptible to the ring nematode (Mesocriconema xenoplax), as confirmed by population recovery tests in pot assays. The grapevine rootstock UCD GRN 3 ensures high technological efficiency during propagation, displaying excellent cutting viability and establishment.

Morphological Description of the Rootstock Variety UCD GRN 3

The morphological characteristics of this hybrid display a prominent visual resemblance to Vitis champinii, but are distinguished by shorter teeth, a thicker texture, and limited lobing of the leaf blade.

• Shoot tips: Enclosed in expanding leaves, green in color (7.5GY 4/4 on the Munsell scale), and sparsely covered with arachnose tomentum.
• Young leaves: Green (7.5GY 4/4), three-lobed, glabrous with fine arachnose tomentum and relatively long, sharply pointed teeth.
• Mature leaves: Medium-large in size (average blade measurements are 10.6 cm in length and 13.7 cm in width). The leaf blade shape is broadly cuneiform to orbicular. The upper surface is glabrous, rugose, and mostly flat with some puckering near the petiolar attachment. The upper leaf surface is green (7.5GY 4/4), while the lower surface is lighter green (7.5GY 5/4). The lower surface features scattered arachnose tomentum, fine bristles along the main veins, and small tufted bristles (domatia) at the intersections of the main veins. The teeth are short and broad with an angular shape. The petiole is medium-sized. The petiolar sinus is an open, narrow U-shape.
• Canes (vines): Mature canes are brown (2.5YR 5/8) and mostly round in cross-section. They are characterized by long internodes and limited lateral shoot development. Nodes feature medium-sized rounded buds. The diaphragm is relatively thick, and the pith is medium-sized.
• Flowers: Pistillate (female) with small clusters. When unpollinated, they produce small black berries.

Nursery Management and Cultivation Features

In nursery management, the rootstock UCD GRN 3 exhibits strong technological performance. Initial phases of the selection process confirmed that dormant two-node cuttings of this variety possess an excellent ability to form roots and callus, directly guaranteeing a high output of first-grade grafted vines in the nursery field. In mother blocks, the rootstock variety UCD GRN 3 produces vines with moderate vigor, developing long, straight canes with moderately long internodes. A significant advantage in mother block cultivation is the limited development of lateral shoots, which substantially reduces manual labor costs for canopy management and simplifies maintenance. Preliminary propagation assays also indicate that the hybrid root system develops moderately deep rooting angles.