Clonal selection is a means of evaluating the agronomic, sanitary and oenological characteristics of a certain number of strains chosen for their specific characteristics in old plots of vines, making it possible to make the most of the natural diversity of the grape varieties. Its objective is to obtain vine plants which do not carry serious virus infections (fanleaf or leafroll diseases) and are able, when cultivated, to provide regular yields and foster the production of quality wines. It therefore makes it possible to offer the wine industry diversified plant material, characterised from a sanitary point of view and with known agronomic and technological behaviour.
What is a clone?
A clone is the vegetative progeny that conforms to a strain chosen for its indisputable identity, phenotypic characteristics and health status (OIV Definition). In plants, any vegetative propagation, whether by layering, cutting or grafting, results in the production of individuals that are strictly identical from a genetic point of view, i.e. clones. It is therefore a natural process, used by humanity since the dawn of time, to select the plant material best suited to their needs.
What is clonal selection?
First of all, clonal selection consists in choosing, during surveys of old vineyard plots or clone conservatories, strains whose behaviour is deemed to best meet the needs of winegrowers. After carrying out sanitary tests for the most serious virus diseases, the individuals are evaluated from an agronomic and oenological point of view. The clones thus characterised, free of serious viral diseases, are kept by IFV at Domaine de l’Espiguette, then multiplied after approval and made available to winegrowers by the nurseries. Clonal selection is based on a long, rigorous procedure and a succession of tasks, all the details of which are specified below. Requiring a variety of skills, techniques and specific equipment, it is managed by the IFV’s Plant Material Centre with the help of the 36 regional partners of French vine selection.
What does this selection method guarantee?
Contrary to received and frequently propagated ideas, this method of selection offers important possibilities for improving and diversifying vine plant material, while preserving the characteristics and identity of the grape varieties. Thanks to the sanitary quality of the plants and by taking into account the diversity of grapes and wines, clonal selection also contributes to enhancing the heritage of all the vine varieties cultivated in France. For example, the following clones are now approved and available: 47 clones of Pinot Noir, 31 clones of Chardonnay, 23 clones of Grenache. The clonal offering for these grape varieties, on which work extended over several generations based on numerous origins of plant material, is much more diversified than certain massal selections, for which prospecting is sometimes limited to only a few plots.
Why was clonal selection developed in France?
It can be considered that the first step towards maintaining and studying the clonal diversity of the vine varieties grown in France was the creation in 1944 of the Section de Sélection et de Contrôle des Bois et Plants de Vigne, under the responsibility of Jean Branas. One of the main objectives of this Professor of viticulture at the National School of Agriculture in Montpellier – besides the need to supply viticulture with homogeneous and clearly identified plant material – was to halt the catastrophic spread of fanleaf disease following the post-phylloxera vineyard reconstruction. The devastating effects of this viral disease, for which the nematode vectors are very resistant, affected a large number of vineyards. This is the primary purpose for which the clonal selection was introduced. This initiative was followed by the creation of Domaine de Vassal (INRA) in Marseillan in 1949. But French clonal selection started in earnest in 1962 with the creation of the National Technical Association for the Improvement of Viticulture (ANTAV), which became ENTAV, and then the French Institute of Vine and Wine (IFV), the infrastructures of which are located in the sandy terrain of Domaine de l’Espiguette at Le Grau du Roi, in the Gard département.
What is sanitary selection?
Sanitary quality is the prime objective of clonal selection. According to European regulations, the selected plant material must be free of the main viral diseases: fanleaf disease, leafroll (types 1, 2 and 3) and mottling (only for rootstocks). Virus screening begins at the time the ortets are selected in the vineyard: plants with obvious visual symptoms are eliminated. Complementary to screening, these viruses are detected using several methods:
• Biological tests (indexing): this consists in placing a graft of a clone to be tested on a cutting, keeping one bud, of a so-called indicator variety capable of showing typical symptoms of the desired viral infection. Indexing can be done by woody (3 years) or herbaceous (6 to 12 months) grafting. This is the reference method for clone approval.
• Serological ELISA (enzyme linked immunosorbent assay) tests: this serological technique is based on the antibody (serum) – antigen (virus) reaction.
• PCR (polymerase chain reaction) tests: the PCR test is a genomic technique which enables a DNA fragment obtained by retro-transcription to be amplified with the help of specific primers, starting from the RNA of the virus. This method is used for provision of services.
What does sanitation provide and when is it feasible?
If no healthy rootstock has been found in vineyards, during prospection or in conservatories repositories?), or in the case of clones of particular agronomic interest but carrying secondary virus diseases, it is possible to sanitize the plant material. Today, the most widely used technique is apex micrografting. This consists of taking an apex (which is virus-free) from a virus-infected plant and micrografting it in vitro onto a hypocotyl (part of the stem between the base and the first cotyledons) of a seedling. Many rootstock clones, for which selection is for sanitary reasons only, have also been sanitized and are now approved and widely multiplied.
What does agronomic and oenological selection consist of?
This evaluation procedure is carried out systematically. It is complementary to sanitary selection and represents the second part of clonal selection. It is carried out in several stages, both at IFV and in the region in which the clone was obtained, in collaboration with the 36 vine selection partners.
Prospecting. This very first stage consists of selecting and carrying out ampelographic description of strains chosen for their characteristics in old vineyard plots or in clone conservatories. During the winter, the shoots of the marked stumps are taken and then introduced to the IFV Plant Material Centre.
Cultivation in containers. After initial sanitary sorting carried out by ELISA and RT PCR tests, each healthy introduced candidate clone is grown in an individualized container. The wood collected may be used for further sanitary selection (indexing) and to make plants for agronomic evaluation in the vineyard.
Study collection. This is an experimental plot, set up in the region of origin of the grape variety by the selection partners, the objective of which is the viticultural and oenological monitoring of the clones obtained by prospection or from conservatories with a view to approval. Established according to a very precise protocol, it is composed only of accessions (individuals) having satisfied the sanitary tests regarding fanleaf disease and leafroll. The requirements for the experiment are as follows:
– Traditional and homogeneous soil and climate (terroir) for the variety to be studied,
– Presence of at least one approved control clone and a maximum number of 20 candidate clones,
– Vineyard monitoring for 5 years, including complete agronomic measurements (bunch weight, fertility, vigour, etc.)
– Vinification and tastings of at least 3 vintages to evaluate the technological and organoleptic potential of the candidate clone,
– Analysis of all the data and decision to apply for approval.
After analysis and synthesis of all the data obtained and after consultation with its partners, IFV requests approval of the clones deemed to be of interest to the sector by the Vine Section of the CTPS (Permanent Technical Committee for Plant Selection). The latter gives an opinion, which the Ministry of Agriculture endorses. The clone is then given an official approval number by FranceAgriMer.
French clones have been widely distributed in France for the past fifty years (and, since 1995, worldwide under the ENTAV-INRA® trademark), attesting to the quality of this selection work. The pursuit of agronomic evaluations enables new selections to be proposed each year with sound cultural, oenological and sanitary guarantees, thanks to the involvement of partners present in all French winegrowing regions.
Is the clonal selection work of guaranteed reliability and quality?
As conducted in France, selection may appear burdensome, fastidious and lengthy (it takes about 15 years to finalize a selection from the time a candidate rootstock is identified in an old plot). However, this duration and the fact that the work is carried out by public bodies or collective structures, without short-term commercial interest, are undeniably a guarantee of the reliability and quality of the selections. Let us underline the cumulative effect of this work in the long term: except for occasional downgrades of certain clones in line with new findings, all the old selections are maintained and remain available, and the range of diversity selected and multiplied is constantly increasing over time. The quality of the evaluations and the continued monitoring of the material over time have also greatly contributed to the recognition and success of French plant material abroad.
Does clonal selection reduce the genetic diversity of grape varieties?
The propagation of a small number of individuals in a given population may result in this, although genuine diversity exists in the variety under consideration. This is not necessarily the case, however (recent crosses that are not very widespread, minority grape varieties of which very few individuals have been found, grape varieties with low apparent variability, etc.). Importantly, clonal selection is not intended to reduce the genetic diversity of grape varieties but to represent it, which requires prior knowledge. Depending on their anteriority, their development and the mutations to which they have been subjected, the grape varieties have generated populations of individuals that may present certain differences. This intra-varietal diversity is expressed in many ways: growth habit, vigour, fertility, phenological cycle, accumulation of sugars, aromatic and/or polyphenolic potential, size and shape of bunches and berries, compactness of bunches, ampelographic characteristics (colour of organs and indentation of the leaves), etc. It is only when broad surveys are carried out that we can gain an objective idea of the variability of the grape variety concerned and ultimately, collect the widest possible diversity to preserve and study it. Diversity is thus naturally enhanced by means of clonal selection, which is no more (as we feel important to point out) than the characterization and exploitation of this diversity. When significant variability is observed within a grape variety (as is the case with Pinot Noir, Chasselas, Chardonnay and Négrette, for example), the objective of selection is to reflect this variability in a certain number of clones developed from as many individuals representative of the different behaviours of the grape variety. This selection work first requires the creation of conservatories in which this diversity can be observed in one single place.
Does clonal selection accentuate the risks of vineyard decline?
What are the differences between clonal and massal selection? Various rumours circulating in winegrowing circles suggest that clonal selection is partly responsible for dieback in vineyards. So far, no scientific study or experiment has been carried out to support this thesis. The drop in yields observed in the vineyards of Burgundy or Champagne is largely caused by the Grapevine fanleaf virus (GFLV). The best way to combat this virus is to use certified material that provides maximum health guarantees, i.e. is the result of clonal selection. As for grapevine trunk diseases, there could be some differences in sensitivity between clones, but this is unfortunately insufficient for the choice of clones to be an effective means of fighting Esca or Black Dead Arm. And the use of material from massal selection will not solve the problem either. Clone conservatories (or repositories), which can be considered as highly concentrated massal selections (up to more than 600 different individuals conserved on the same plot), are as much affected by grapevine trunk diseases as the clonal plots, and some of them have to be regularly renewed and relocated owing to the large number of missing individuals observed.
Does clonal selection foster identical-tasting wines?
This is now a widespread idea but it is completely unfounded. Firstly because the clone effect is far less important than the effect of the soil, the terroir, the rootstock, the climate or the work of the winegrower. In 2005-2006, the selection partners conducted trials as follows:
• separate vinification of the clone considered to be of the highest quality,
• vinification of a blend of 4 to 15 clones.
This work was carried out on Cabernet-Sauvignon, Pinot noir, Gamay, Riesling, Grenache and, with tastings to support it, showed that in the vast majority of cases, the clone reputed to be the best is more appreciated than the blend. Why is the argument that clonal selection fosters identical-tasting wines wrong? Because, with a view to diversity, the advice given by breeders systematically stresses the importance of planting several clones of the same grape variety on a plot or farm. Lastly, the data sheets of the Official Catalogue of Vine Varieties and Clones Grown in France differentiate clone behaviour according to region. The most edifying example is that of Pinot noir. A “Burgundian” Pinot noir N clone is not suitable for the production of sparkling wines. Conversely, trying to make a still red wine with the Pinot noir clone 386, which comes from Champagne and is specifically suited to the production of sparkling wines, would be a real challenge! Moreover, clone 777, which in Champagne is considered as not very typical, is used to make sparkling wines virtually only in Tasmania.
What are the differences between clonal and massal selection?
Various rumours circulating in winemaking circles suggest that clonal selection is partly responsible for dieback in vineyards. So far, no scientific study or experiment has been carried out to support this thesis. The drop in yields observed in the vineyards of Burgundy or Champagne is thus largely caused by the Grapevine fanleaf virus (GFLV). However, the best way to combat this virus is to use certified material that provides maximum health guarantees i.e. that is the result of clonal selection. As for grapevine trunk diseases, there could be some differences in sensitivity between clones but unfortunately insufficient for the choice of clones to be an effective means of fighting Esca or Black Dead Arm. And the use of material from massal selection will not solve the problem either. The clone conservatories that can be considered as highly concentrated massal selections (up to more than 600 different individuals kept on the same plot) are as much concerned by grapevine trunk diseases as the clonal plots, and some of them have to be regularly renewed and relocated due to the important number of missing individuals observed. Massal selection is used by winegrowers with the main objective of conserving the viticultural heritage of an old vine. It consists of identifying the most worthwhile plants on the plots, sampling and propagating the vine shoots, and then replanting them. If no sanitary tests are conducted at the same time, this approach can be very risky with regard to the transmission of the principal virus diseases, fanleaf disease and leafroll. Unlike clonal selection, which includes a whole set of agronomic evaluations accompanied by sanitary tests that guarantee that the plant material is free of the main virus diseases, massal selection does not ensure that all the desired agronomic and oenological objectives are achieved safely. On the other hand, in the case of certain rigorous massal selection initiatives using sanitary testing and observation of strains over several years prior to the selection of a certain number of individuals for propagation according to defined objectives, the two approaches can be considered similar. In this case, the difference between the two approaches lies mainly in the number of individuals presenting the desired behaviour which will go on to be propagated, and tends to be cancelled out if successive selection increases the number of approved clones available. It is all the more regrettable, therefore, that some massal selection procedures are prized simply for the fact that they do not include the word “clone”. What matter how good a selected breed is as long as it is not obtained by clonal selection! Yet individuals propagated by massal selection are also, originally, clones of pre-selected strains.
Conservation of vine genetic resources in France
Vine genetic resources in France are conserved according to three complementary levels:
– The central ampelographic collection of INRAe at Domaine de Vassal, in the Hérault département, is composed of vines from 54 wine-producing countries, representing: 2,700 grape varieties, 350 wild vines, 1,100 interspecific hybrids, 400 rootstocks and 60 species of Vitaceae. This richness and diversity make it a unique ampelographic collection anywhere in the world.
– National conservatory of the initial clone material selected by IFV, at Domaine de l’Espiguette in the Gard département, composed of more than 4,570 clones representing 581 varieties (table grapes, wine grapes, rootstocks), including 1,947 clones approved since the beginning of clonal selection. These clones come from 20,000 individuals introduced and tested since 1962.
– Regional conservatories of the 36 vine selection partners: 180 conservatories established in all French winegrowing regions, representing 136 varieties listed in the National Catalogue out of a total of approximately 20,000 different individuals preserved nationwide.
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