GRAD® Millardet et de Grasset 420A, Clone 1

In GRAD’s opinion, and based on nearly two decades of observation, the best rootstock for use in close-planted high quality vineyards, and in particular those planted to the Pinot varieties. The GRAD®1 clone is free of detectable virus by PCR test, and was specially selected, through ten years of trials, for its superior robustness and exceptional level of tolerance for dry soil conditions.

GRAD®1 clone 420A in brief:

  • Unique new D.N.A.-identified GRAD® clonal re-selection from old M.A.F. experimental heat-treated source
  • Specifically selected over ten years of trials for its robustness and unusually good tolerance of dry soil conditions
  • Highly tolerant of (up to 20%) free lime in soil, but by no means of utility only in calcareous soils
  • In my opinion, and based on nearly two decades of observation, the best rootstock for use in close-planted high quality Pinot noir vineyards, because of its marked capacity to produce balanced vines in high-density plantings and the similarity of its adaptations and performance to those of the root system of Pinot vines
  • The GRAD®1 clone of 420A is free of detectable virus by P.C.R. test and thus, unlike the ex-U.C.D. clonal line used by a number of New Zealand nurseries (other than Stanmore Farm), does not carry Fleck virus. This means GRAD®1 clone 420A gives healthier, longer-lasting graft unions and, especially, superior scion photosynthesis and ripening in cool autumns. I recommend therefore that this high quality 420A clonal line should ideally be grafted only with Fleck-free clones to retain this important phenological advantage
  • Advances scion maturity and increases scion fertility, but also has a long phenological cycle that allows ripening to continue in cool autumns well after Vitis riparia and V. riparia x V. rupestris stocks (and 5C and SO4) shut down for the season
  • Vines grafted with GRAD®1 clone 420A rootstock are available in New Zealand through Stanmore Farm nursery under license from GRAD®.
  • Website:
    E-mail for orders or inquires:
    Phone: 0800 Stanmore (0800 782 666)
    Mobile: 027 544 0140
  • For more information on this rootstock, or advice about its use and suitability, contact Dr. Gerald Atkinson at
  • A comprehensive non-propagation contract must be signed off as part of your purchase order.
  • Download single A4 page ‘GRAD 420A In Brief’ fact sheet PDF


Source and History

The GRAD®1 clone of 420A derives, by a process of several re-selection stages, from a remnant vine sourced from an old M.A.F. experimental block. I initially made around 20 replicates of the original remnant 420A vine after its identity was confirmed by D.N.A. testing. These were exposed to lengthy and detailed experiments and observations at the GRAD® r&d nursery in Christchurch to identify the single most robust and drought-resistant selection. Ultimately one plant clearly stood out as consistently the most superior and hardy of all. In particular, it was distinguished by its  ability to withstand, and to robustly recover from, lengthy water deficit. This then became the foundation mothervine of the GRAD®1 clone of 420A.

In 1887, Alexis Millardet obtained the 420A hybrid by crosing what very recent studies have shown is a still unknown selection of V. berlandieri (the same as that which was probably also used by Couderc to obtain 161-49) with an also unknown selection of V. riparia. The relatively small glossy dark green leaves and pink-edged shoot tips of 420A bespeak an uncommon V. berlandieri line and in some respects underscore the validity of recent reclassification of this ‘species’ as merely a type of Vitis cinerea.


Health status

The GRAD®1 clone of 420A has been proven to be free of detectable virus by PCR test. Subsequent E.L.I.S.A. tests on the GRAD®1 nursery foundation vine for GLRaV1,2,3, and GVA were all negative / clear.



In its growth habit, 420A is particularly distinguished as a stock that is initially slow to develop its root system.  (This also largely underpins its reputation for low-vigour.) Accordingly, GRAD strongly recommends judicious fertigation of young vines grafted with 420A to push along the root system’s establishment in the first 3 to 5 years after planting. This is much wiser than just leaving young vines grafted on 420A to battle away regardless of their otherwise slow rate of establishment. Similarly, weed competition can quickly and deleteriously impact on this rootstock as it establishes — as is very much also the case of course for those grafted to V. riparia and V. riparia x V. rupestris stocks.  Neglect is not the way to develop a stand of good quality vines on 420A therefore, although once established, it is a very reliable stock for premium, well-managed, vineyards, and especially so in close-planted / high-density plantings. Moreover, as is detailed below, its ability to tolerate drought — for which the GRAD®1 clone of 420A was specially selected — significantly improves and increases over time, provided its is in clay or heavy loam soils. (Use in free-draining gravels or shallow soils is therefore not recommended.)

It must be added that as with every other rootstock, 420A is not a ‘devigourating‘ stock: no such grapevine rootstock exists. Indeed, in the right conditions 420A can produce significant excess vigour —but this involves circumstances which should not be tolerated in any well managed vineyard. Nevertheless, I have seen very out-of-balance, highly over-vigorous, Pinot noir grafted on 420A where the high level of scion vigour was clearly driven by significant over-irrigation in generously fertile soil. Thus if fed and watered to gross excess, 420A will produce ‘triffid’ vines — just like any other rootstock. But, more realistically, while it is certainly responsive in its establishment phase to generous feeding and watering to ‘beef it up’ , the  GRAD®1 clone of 420A  can be readily controlled by deficit irrigation and measured nutrient application so as to give high quality balanced vines. This is particularly so in high-density plantings, for which it is an outstanding choice as a rootstock — arguably without peer among the range of rootstocks available in New Zealand .

In the literature, opinion and reports are divided regarding the drought resistance of 420A. However, a close reading of numerous studies of this stock’s performance suggests that the key variable in determining its tolerance of, and performance under, significant water deficit is the vineyard’s sub-soil clay content.  The published evidence thus suggests that over time, provided 420A is planted in heavy loams or in clay soils, it can sustain a range of planting densities and develops an increasing level of drought tolerance. Thus, for instance, Perold reported that in South Africa  420A was drought resistant in precisely such conditions. In fact, he considered it the best rootstock for that country’s vineyards — although clearly this is based on the assumption that the 420A is planted in soils that retain sub-soil moisture. To this however, it must be added that 420A is not adapted to wet, poorly-draining, soils; moisture retention in the sub-soil is one thing; poor drainage is quite another — and 420A will not tolerate it. There are good indications then in the literature which support the view that over time 420A becomes more able to resist drought because it progressively exploits deeper, more damp, sub-soil levels, albeit from a low-and-slow starting point, as it were. (This is highly suggestive of a low-vigour form of Vitis cinerea adaptation whereby slow but progressive exploitation of deeper sub-soil levels is a key, if gradual, adaptation to drought. However, to this it must be added that the  GRAD®1 clone of 420A  has also shown exceptional tolerance to significant soil moisture deficit right through the full depth its root column — a further feature of V. cinerea, but one not so frequently or so strongly associated with 420A.)

At the GRAD® R&D nursery, GRAD®1  420A performed most impressively in very dry conditions in repeated pot trials where each vine’s soil mix was allowed to dry out completely before they were given water. As a simple comparison, all potted vines of Schwarzmann and 3309 in this trial died rather early in the course of these experiments because they could not tolerate the drying out of their root mass. I have continued this trial for ten years now, with the original GRAD®1  420A mothervine now in a PB95 poly-bag ‘pot’ and it still continues to survive and recover from extremely limited watering and no exposure to rainfall. Clearly therefore, this clone is a genuine ‘hardy survivor’ genetic line. It does not however show the speed of recovery after drought that the GRAD® clones of 44-53, 106-8, or, especially, GRAD® DRC5 Super possess. Nevertheless, in conditions far more extreme than would be tolerated in any sensibly managed New Zealand vineyard, the original GRAD®1  420A mothervine continues to flourish: I dry it right out and only then give it water and a feed, and it recovers well for yet another season of trials. On balance of course, a more conservatively realistic approach is advisable, whereby the GRAD® 1  420A clone should be regarded as moderately drought resistant when well established, but with the caveat that the more clay-rich the sub-soil it is in, the better it will perform.

Typically for a 420A line, the GRAD®1  clone must be watched for its disposition to cause over-cropping of its scions in the vines’ early years of production. This is important, because without either thinning of extra nutrition, allowing big crops on young vines grafted to 420A can rather readily run its vines out. Once again, moderation and sensible viticultural management is the key.


Qualitative potential

Although it can be induced to develop a fairly large root system over time if fed and watered very generously, GRAD®1  420A is not a stock that has been developed for general use in wide-spaced, high production, ‘industrial’ vineyards. It is however a superb stock for intensively managed super-premium high density plantings on clay and (lower-fertility) heavy loam soils. In Europe, 420A is widely recognised as a leading stock for the production of high quality low-cropped fruit, and it is used accordingly in Bordeaux, Burgundy and elsewhere in France, as well as in Austria, Bulgaria, Germany, Spain and Portugal, Italy, Romania and Turkey. It also needs by no means to be confined to, or regarded as of use only for, vineyard with calcareous soils — any more than would be the case for 5C, SO4, etc.


Ripening period

420A advances fruit maturity. It is also generally a very good ripener of its scions’ fruit in cool autumns because of its 4 to 6 weeks longer phenological cycle compared to V. riparia, or V. riparia x V. rupestris stocks. (Growers in Central Otago, Nelson, and Waipara in particular should note this.) This means vines grafted with 420A tend to show significantly later senescence because of its disposition to sustain photosynthesis in cool later-autumn conditions. Undoubtedly, this is an inheritance from its particular V. cinerea parent, and it means this stock cuts a significant contrast in this regard compared to V. riparia or V. riparia x V. rupestris or quite a few other V. berlandieri / V. cinerea x V. riparia stocks.



GRAD’s licensed New Zealand nursery, Stanmore Farm, has 420 A GRAD®1 clone mothervines in full production. For current season and forward orders, contact Stanmore Farm for details regarding grafting quantities available.

Vines grafted with GRAD®1 420A rootstock are available through Stanmore Farm nursery under license from GRAD®

E-mail for orders or inquires:
Phone: 0800 Stanmore (0800 782 666)  
Mobile: 027 544 0140

For further details and advice on utilisation and suitability for your vineyard, contact Dr. Gerald Atkinson at

Please note that a strict and comprehensive non-propagation contract must be signed off as part of your purchase order.

GRAD® is a New Zealand registered trademark uniquely and exclusively used to identify the vines in the GRAD® vine collection. Use by unauthorised parties to identify any vine material, or other use for commercial gain, is an infringement of this trademark.

Genetic ‘fingerprinting’ and clonal traceability

Vine pirates BEWARE! It is now possible to genetically fingerprint, uniquely identify, and detect grapevine clones using the latest-developed molecular genetic sequencing techniques. See the breakthrough research paper by Michael J. Roach et al, “Population Sequencing Reveals Clonal Diversity and Ancestral Inbreeding in the Grapevine Cultivar Chardonnay”, published November 20, 2018 at



Questions about this rootstock? Contact us.

Author: Dr. Gerald Atkinson

Company director, viticulturist, grapevine researcher and historian, and sometime wine-writer.