420 A Millardet et de Grasset
Name of vine variety in France (and common name)
420 A Millardet et de Grasset (420 A MGt)
Breeder and year of obtention
Alexis Millardet and Charles de Grasset, 1887
Genetic origin
This root stock is derived from the crossbreeding of Vitis berlandieri and Vitis riparia.
Evolution of areas under rootstock nurseries
1945 1955 1965 1975 1985 1995 2005 2015
Rank 6 10 12 12 12 14 12 14
ha 68 100 107 71 39 25 49 25
Estimated surface area of French vineyards grafted with this rootstock and the main areas of use
13 000 ha. Aquitaine, Rhône-Alpes, Languedoc-Roussillon, Midi-Pyrénées, Bourgogne Franche-Comté, Provence-Alpes-Côte d’Azur
Ampelographic description
Identification signs include:
-the tips of the young shoot which are half-opened to closed have a moderate coat of flat-lying hairs,
- the young leaves are slightly bronze colored,
-elongated shoot with an elliptical section with a ribbed contour; the internodes and the red nodes on the dorsal side and the underside with green inter-nodes and red nodes up to the tips with an absence of upright hairs,
- adult leaves are dark green, shiny, wedge shaped, whole and sometimes 3 or 5 lobes forleaves at the base with an open U-shaped petiolar sinus, moderate anthocyanin pigmentation of veins and the underside with a sparse caot of upright hairs,
- male flowers, yellow to reddish brown vine shoots
Genetic profile
Allel 1 124 236 231 238 191 256 238 243 263
Allel 2 135 261 262 270 196 256 270 245 263
Resistance to soil parasites
420 A MGt displays a high tolerance level to radicicolae phylloxera. Its resistance to the nematodes Meloidogyne incognita and Meloidogyne arenaria is also good.
Adapt to environment
420 A MGt resists up to 35% total limestone, 20% active limestone and a CPI of 40. Its resistance to ferric chlorosis is considered as moderate to good. It appears well adapted to fertile conditions in addition to fairly deep clay limestone soils with sufficient water supply.It is on the other handnot well adapted to compact soils and excessive spring humidity. This root stock has difficulty in absorbing potassium in the soil. The grafted varieties, particularly the most sensitive, can frequently show signs of potassium deficiency with this root stock.
Interaction with grafts and production objectives
The graft vigor of this root stock is low and vine trunk development is limited. It does however tend to delay maturity. 420 A MGt encourages floral initiation. Given it vigor, yields should be limited, particularly during the beginning production years to avoid unbalanced vine trunks. 420 A MGt produces good results with Cabernet franc N, Merlot N and Tannat N.
Aptitudes for plant propagation
Wood production is moderate (30 000 to 60 000 m/ha) with vine shoots which lignify easily but the diameter of the internodes is sometimes thin.  There is subtantial growth of quick buds. The cutting aptitude of 420 A MGt is low and its grafting capacity is moderate. In order to improve the recovery percentage from cutting, more substantial hormoning may be applied.
Resistance to aerial parasites
The degree of tolerance of 420 A MGt to gallicolae phylloxera is moderate and it displays good resistance to downy mildew.
Clonal selection in France
Les 5 clones agréés de 420 A MGt portent les numéros 10, 11, 169, 241 et 758.