Clonal selection
Clonal selection is a process of evaluating the agronomic, sanitary, and oenological characteristics of a certain number of vines chosen for their specificities in vineyards, allowing to enhance the natural diversity of grape varieties. Its objective is to obtain vine plants free of viruses and whose cultural aptitudes provide a regular production and promote the production of wines that meet the needs of winegrowers.
Description
Clonal selection consists of choosing, during surveys in old vine plots or in clone conservatories, stocks whose behavior could best meet the needs of winegrowers. After conducting sanitary tests for certain viruses (fanleaf, leafroll), healthy individuals are evaluated from an agronomic and oenological point of view. The clones thus characterized, free of viruses, are conserved at the Plant Material Center of the IFV (French Institute of Vine and Wine) at Domaine de l’Espiguette (30), which is the national conservatory, then multiplied after approval and made available to nurserymen. Ultimately, these can supply their clients.
Clonal selection is based on a long and rigorous procedure, requiring diverse skills, specific techniques, and equipment. From surveys to clone approval and multiplication, it takes on average 12 years. It is managed by the IFV Plant Material Center in coordination with the GEVES (Study and Control Group for Varieties and Seeds) with the assistance of the 36 regional partners of the French Vine Selection[1].
Objectives
- Improvement and diversification of the vine plant material, while preserving the characteristics and identity of the grape varieties.
- Enhancement of the heritage of vine varieties through the sanitary quality of plants and the diversity of grapes and wines.
- Offer winegrowers clones that best correspond to their needs.
As examples, to date : 47 clones of Pinot noir, 31 clones of Chardonnay, and 23 clones of Grenache are approved[1]. For more confidential varieties, there are often 1 to 2 approved clones, such as for Tibouren or Aubun for example.
Implementation
Identification
To identify the vines meeting expectations, a survey in old vine plots or clone conservatories must be carried out: this very first step consists of selecting and ampelographic description of the chosen stocks. These observations are made from spring until harvest. During winter, canes from the marked stocks are collected and then introduced into the IFV clonal selection center.
Sanitary selection
Sanitary selection consists of verifying the absence of viruses (fanleaf and leafroll for all material + leafroll virus for rootstocks). Depending on the variety’s purpose (grape or rootstock), requirements differ.
Different techniques can be used, the most common being ELISA tests (Enzyme Linked Immuno Sorbent Assay). This is a serological technique based on the antibody (serum) - antigen (virus) reaction. The addition of an enzyme to the antibodies reveals the presence of the virus by a color reaction if it is present in the sample to be tested.
Genetic selection
Genetic selection is mandatory and complementary to sanitary selection. It consists of evaluating the agronomic and oenological performances of candidate clones. Study plots with a certain number of repetitions are established according to a precise protocol (INRAe-IFV-CTPS), allowing comparison of the behavior of the candidate(s) with at least one known reference clone or, for a first selection, a representative grape variety of the production area.
It is carried out in five steps, both at IFV and in the clone’s region of origin, in collaboration with IFV’s local partners consisting of Departmental Chambers of Agriculture, Interprofessional Committees, associations, or winegrowers’ unions.
The 5 steps of genetic selection
- Survey in old vine plots or clone conservatories : See Identification.
- Container cultivation : After an initial sanitary sorting by ELISA tests, each healthy introduced clone is grown in an individual container. The collected wood can be used for further sanitary selection (indexing) and to produce plants for agronomic evaluation in the vineyard.
- Study collection : This is an experimental plot established in the grape variety’s region of origin, aimed at viticultural monitoring of clones (for 5 years: phenology, fertility, yield, vigor, maturity control) and oenological evaluation (vinifications and tastings by professional and expert panels for at least 3 vintages).
- Data analysis and approval request : After analysis and synthesis of all obtained data and consultation with its partners, IFV and/or its partners request approval of clones deemed interesting for the sector from GEVES, in coordination with the vine section of the CTPS (Permanent Technical Committee for Selection). The latter issues an opinion which the Ministry of Agriculture usually endorses. The clone is then assigned an official approval number by FranceAgriMer, allowing multiplication to begin at nurseries.
- Behavior plots : These plots study approved clones at a given site to compare their cultural characteristics and technological aptitudes according to environmental factors. Monitoring these plots mainly allows dissemination of usage advice to winegrowers in the region. It is also a valuable source of reliable agronomic references[1] [2].
Once clones are approved, the multiplication step to obtain certified plants can begin.
Multiplication
This process aims to produce sufficient plant material with maximum sanitary and agronomic guarantees (certification) to supply French viticulture through viticultural nurseries. Starting from the clone head, the sector organizes a pyramidal multiplication process involving three categories of material.
Initial material
Produced from clone heads (5 to 10 stocks). The grafted-welded (or rooted for rootstocks) resulting from these allow the establishment of pre-multiplication plots. These are exclusively established at approved establishments (14 in France), on plots that must have been vine-free for over 20 years.
Basic material
Derived from pre-multiplication, this material is used to establish mother vines for scions or rootstocks at nurseries or multiplying winegrowers. Soil rest is at least 10 years in this case, and all material must have been hot-water treated before planting (bath at 50 °C for 45 minutes), as part of prophylactic control against flavescence dorée phytoplasma.
Certified material
These vines allow the mass production of certified material (scions and rootstocks), implemented by nurseries to meet the needs of viticulture.
This method allows obtaining significant quantities of material. Strict control is carried out at each level, both on establishments and on the material itself, providing the sector with sanitary security and traceability guarantees for the certified plant material distributed[3].
Is clonal selection a guarantee of reliability and quality?
As conducted in France, this work may seem heavy, tedious, and very long. However, this duration and the fact that the work is carried out by public organizations or collective structures, without short-term commercial interest, undeniably constitute a guarantee of reliability and quality of the selections. In the long term, one can highlight the cumulative effect of this work : except for occasional downgrading of some clones based on advancing knowledge, all old selections remain maintained and available, and the range of selected and multipliable diversity only grows over time. This quality of evaluations and the sustainability of material monitoring over time have strongly contributed to the recognition and success of French plant material abroad[4].
Risks
Does clonal selection reduce the genetic diversity of grape varieties?
Multiplying a reduced number of individuals from a given population can lead to this result, if a real diversity exists in the considered variety. Clonal selection rather aims to represent the genetic diversity of grape varieties, which requires prior knowledge. Grape varieties, depending on their age, development, and mutations they have undergone, have generated populations of individuals that may present some differences among them. This intra-varietal diversity expresses itself in many ways : habit, vigor, fertility, phenological cycle, sugar accumulation, aromatic and/or polyphenolic potentials, pruning and shape of clusters and berries, cluster compactness, ampelographic characteristics (color of organs and leaf shape)… Only when broad surveys are conducted can the variability of the concerned variety be objectively apprehended, and ultimately, the widest possible diversity gathered to preserve and study it; this is the role of grape conservatories.
Enhancement of diversity thus naturally occurs through clonal selection, which is nothing other than the characterization and exploitation of this diversity. It should be noted that depending on eras and production areas, market needs will orient towards multiplication of clones that can be very different from each other.
Does clonal selection increase the risks of vineyard decline?
Currently, no scientific study supports this thesis. Yet, the best way to fight decline is precisely to use certified material providing maximum sanitary guarantees and thus resulting from clonal selection. As for the impact of wood diseases, it is more related to variety, pruning method, and grafting method than to the nature of clones[1] [4].
Sources
This article was written with the kind contribution of Garance Marcantoni, Organic Agriculture Project Manager. Viticultural advisor - Organic viticulture referent for PACA and national. Plant material referent.
Other sources :
- What is clonal selection? - IFV.
- Clonal selection - IFV Occitanie.
- Clonal selection - Pl@ntgrape.
- History of a plant: from initial to certified - IFV Occitanie.
- Clonal selection, a major advance for viticulture in 16 technical questions - IFV.
- ↑ 1.0 1.1 1.2 1.3 https://www.vignevin.com/innovation-varietale/selection-clonale/
- ↑ https://www.vignevin-occitanie.com/fiches-pratiques/la-selection-clonale/
- ↑ https://www.vignevin-occitanie.com/publications/articles-techniques-et-scientifiques/materiel-vegetal/histoire-dun-plant-de-linitial-au-certifie/
- ↑ 4.0 4.1 https://www.vignevin.com/wp-content/uploads/2018/11/Plaquette_selection_clonale_DEF.pdf
