Viticulture

A few words on grapevine winter buds and pruning in consideration of sap flow Publisher's note: This article presents a pruning practice, fairly widespread in the profession, that is the subject of current research (not presented in this article). The results of this work, that aim at scientifically determining the effectiveness, or otherwise, of these practices, will be presented later in IVES and its media. Original language of the article: English.

One objective of pruning it to manage yield per vine (or per m2) and this is achieved by regulating the number of latent buds (i.e.  buds which bear the primordia of inflorescences).  For many year growers and wineries have been interested in what is currently called: gentle pruning, precision pruning, or pruning with respect to sap flow! But what is hiding behind these concepts?

This article aims to summarise some principles linked to what we could call “gentle pruning”. We will detail i) pruning methods that limit or minimize pruning wound size/surface area on grapevine arms and spurs ii) and pruning that allows for a morphology that is conducive to continuous sap flow versus the ‘hydraulic isolation’ of regions within the vine.

Let’s share to introduce the article a few words on grapevine dormancy and latent bud organisation.

A few words on grapevine dormancy

Grapevine dormancy is an important phenological period comprising of both endodormancy and ecodormancy. Endodormancy is the inhibition of growth originating from the latent bud meristem. It is brought about by internal factors within the plant, which prevent the breakage of dormancy even if external factors are optimal for growth. Aside from hormonal regulation, endodormancy is triggered by shorter days and cooler temperatures. Winter chilling is then necessary to overcome endodormancy. Although the effect of chilling temperature on dormancy release needs further research at the molecular level, a 200 hour-period (eight days) with a mean daily temperature ≤ +8°C proved to be efficient to permit the buds to break within a reasonable duration and to an acceptable level.

When endodormancy has been overcome, grapevine varieties are physiologically ready for bud break, however conditions that lead to ecodormancy must now also be surpassed. Vines can exist within an ecodormant state if environmental factors that support root activity and bud growth are not optimal. These main environmental factors permitting budbreak include warm temperature (air and soil; > +15 °C) and soil water refilling1.

A few words on the latent buds in grapevines

The latent bud is a compound of vegetative miniaturised axils protected by scales2. The principal axil of this compound is called the latent primary axil, which will develop into the future primary shoot (year n+1). The budbreak of the latent buds at each node of the primary shoot (year n) is first inhibited by the hormonal release from the primary shoot and the prompt bud which form the shoots called laterals.

This nascent structure in the latent bud differentiates over 2 to 4 months simultaneous to the growth of the bearer shoot before entering into endodormancy (around August in the Northern Hemisphere). Its phyllotaxic plane is perpendicular to that of the prompt bud and consequently the new developed shoot (year n+1) will grow in a parallel plan to that of the bearer shoot/cane.

The meristem which initiated the primordia of leaves and inflorescences in latent buds (year n) pursues its development after budbreak (year n+1). The developing shoot is named the proleptic axil. The potential fertility represents the number of incipient inflorescences developed on the primary shoot (on average 1 to 3 primordia of inflorescences per latent bud), which will form the future grapes. This fertility depends on the cultivar, rootstocks and on the climate (mainly temperature, light and water) and trophic conditions of the year in which the bud is formed.

The main bud primordium of the latent bud, which is a complex of three bud primordia, bears 70-80% of the potential yield.

While pruning, some basic principles need to be considered for grapevine sustainability

Gentle pruning was known and practiced in French vineyards as early as the early 20th century (as published by Lafon R., 19213). Strangely, these practices were forgotten for decades but have been reintroduced and practised worldwide in vineyards for the past 20 years. Let’s share some information about gentle pruning in this article; here we present a synthesis of some books, published research articles and personal results from the authors.

Pruning is a traumatic cultural practice for vines irrespective of the pruning method (hand or mechanical pruning). In this regard, it is important to distinguish two founding principles which are not always dependant on each other: i) to reduce the size of the pruning wounds (to be adapted and reasoned according to the situation); ii) to respect the hydraulic flow between the vine organs (trunks, arms, spurs).

Let’s mention a few rules of gentle pruning:

1. As published by Lafon R. (1921) it is crucial to respect the sap flows by positioning the pruning wounds, when possible, on the same side of the arms and spurs (figure 1).

Figure 1. Example of pruning wounds which have been positioned over years on the same side of the arms and the associated spurs (yellow arrows). This promotes the anatomical isolation of the pruned organs while maintaining the hydraulic integration across the plant.

2. In the case of cane/Guyot pruning4 5, to avoid the formation of a willow head.

3. To prevent the creation of dead zones (desiccated cones) within the perennial organs (trunk, arms, spurs…) by avoiding cuts in close proximity to the wood (figures 2, 3).

Figure 2. Example of proper spur (cordon) pruning respecting the sap flow of the arm and the spurs. (A) Applying gentle pruning will lead to the increase in the size of the spurs year after year; (B) Gentle pruning does not induce necrotic tissue formation in the arm and spurs.

Figure 3. Example of inappropriate spur pruning on a cordon that has resulted in tissue necrosis of the arm and the spurs, interrupting the conduit for sap flow. (C) Necrotic/dead spurs on a cordon due to inappropriate/bad pruning; (D) Inappropriate pruning has induced wood/tissue necrosis at the spur and arm levels, impacting on sap flow and on vine sustainability.

4. Therefore, in wood older than 1 year, a portion of wood should be left while pruning. The length should be 1,5 or 2 times the diameter of the pruned organ, as presented in figure 46.

Figure 4. (A, B) Examples of inappropriate pruning cuts which have been made too close to the adjoining wood (conducting tissues) (orange arrows). (C) A portion of internode should be left while pruning (the length should be 1,5 or 2 times the diameter of the pruned organ; yellow arrows).

5. The consequence of leaving a portion of the wood, however, could be the development of the basal buds which will require some extra work by cleaning/removing these growing shoots in spring.

6. The role of the diaphragm (figure 5) of the cane is to protect the node and the associated latent bud from necrosis or bio-aggressor infection as a result of pruning. It acts by isolating the pith between successive internodes7.

Figure 5. The diaphragm is located at the node level and is present in a one-year cane (a) and three-year stem (b). Photo (a) is showing starch colored in violet by the Lugol and located in the parenchyma cells of the xylem II.

7. To protect the latent bud from damage due to the pruning wounds located above it, it is recommended to leave a section of internode long enough (at least 2 cm) above the chosen latent bud which bears the future crop (figure 6). In certain wine regions (Champagne, Charentes, Argentina Atlantic coast…), the length of the necrosis can be more extensive and is also dependent on the variety. For these situations, one solution is to retain the full internode above the latent bud.

Figure 6. The wound created while pruning a winter cane (a) will lead to the necrosis of the conducting tissues just below the wound. The length of the necrotic region does not exceed 0,5 to 1 cm under certain climatic conditions. (b, c) show the dead tissues (brown zone) in comparison with the living conducting tissues (xylem, phloem) around 10 weeks after pruning (Shiraz).

8. Irrespective of the training system it is crucial to allow for the continuous development of living wood (which means to avoid the formation of dead wood) which will lead to an increase in the diameter of the arms and the spurs (figure 2).

The general aims of gentle pruning respecting the sap flow are:

i) to avoid the gradual yearly build-up of necrotic-dead wood/tissues,

ii) to maintain the vascular system (xylem-phloem) operational.

Why apply gentle pruning?

Avoiding tissue necrosis due to pruning wounds, and therefore respecting the vine’s hydraulic integration8, will improve vine and vineyard sustainability and will help:

a) To achieve more homogeneous budbreak and primary shoot development, and therefore homogeneous vines, considering that proper sap flow pathways are needed for shoot development.

b) To achieve a better fruit zone microclimate (depending on the vegetative expression/vigour of the vines) by increasing the height of the spurs over years on a cordon.

c) To avoid the spread of wood diseases (Esca, Botryosphaeria dieback…), another goal of gentle pruning (taille "non mutilante")9.  

Notes

  • Pellegrino A., Rogiers S., Deloire A., (2020). Grapevine Latent Bud Dormancy and Shoot Development, IVES Technical Reviews, https://ives-technicalreviews.eu/article/view/3420
  • Torregrosa L., Carbonneau A., Kelner J.J. (2021). The shoot system architecture of Vitis vinifera ssp. Sativa, Scientia Horticulturae 288, https://doi.org/10.1016/j.scienta.2021.110404
  • Lafon R., 1921. Modification à apporter à la taille de la vigne dans les Charentes, Taille Guyot-Poussart mixte et double, Arts & Arts Editions, Bordeaux (réimpression en 2021 de l’édition originale de 1921, éditée à Montpellier).
  • Simonit M., (2015). Guide de la taille Guyot, Editions France Agricole.
  • Sicavac, (2015). Manuel des pratiques viticoles contre les maladies du bois, BIVC, Sicavac Centre-Loire, Imprimerie Paquereau, ISBN 978-2-37006-000-6.
  • Cholet C., Martignon T., Giudici M., Simonit M., Geny L. (2017). Vigne: pourquoi tailler moins ras aide à freiner l'esca. Phytoma, Groupe France Agricole, 2017, pp.38-41. ⟨hal-01603357⟩
  • Faúndez-López P., Gutiérrez-Gamboa G., Moreno-Simunovic Y., (2021). The role of diaphragm as a natural resistance to the necrosis produced by pruning cuts, IVES Technical review, DOI: https://doi.org/10.20870/IVES-TR.2021.4817
  • McElrone A.J., Manuck C.M., Brodersen C.R., Patakas A., Pearsall K.R., Williams L.E., (2021). Functional hydraulic sectoring in grapevines as evidenced by sap flow, dye infusion, leaf removal and micro-computed tomography, AoB PLANTS, Volume 13, Issue 2, April 2021, plab003, https://doi.org/10.1093/aobpla/plab003
  • Lecomte P., Diarra B., Boisseau M., Weingartner S., Rey P., (2021). Preventing ESCA in Vitis vinifera by proscribing vine training systems or mutilating pruning methods, IVES Technical Reviews, DOI: https://ives-technicalreviews.eu/article/view/4734

Authors


Alain Deloire

alain.deloire@supagro.fr

Affiliation : University of Montpellier (L’institut Agro), France

Country : France


Carole Dumont

Affiliation : Simonit & Sirch, Italy

Country : France


Massimo Giudici

Affiliation : Simonit & Sirch, Italy

Country : Italy


Suzy Rogiers

Affiliation : NWGIC, Department of Primary Industries-NSW, Australia

Country : Australia


Anne Pellegrino

Affiliation : University of Montpellier (L’institut Agro), France

Country : France

References

  • Pellegrino A., Rogiers S., Deloire A., (2020). Grapevine Latent Bud Dormancy and Shoot Development, IVES Technical Reviews, https://ives-technicalreviews.eu/article/view/3420
  • Torregrosa L., Carbonneau A., Kelner J.J. (2021). The shoot system architecture of Vitis vinifera ssp. Sativa, Scientia Horticulturae 288, https://doi.org/10.1016/j.scienta.2021.110404
  • Lafon R., 1921. Modification à apporter à la taille de la vigne dans les Charentes, Taille Guyot-Poussart mixte et double, Arts & Arts Editions, Bordeaux (réimpression en 2021 de l’édition originale de 1921, éditée à Montpellier).
  • Simonit M., (2015). Guide de la taille Guyot, Editions France Agricole.
  • Sicavac, (2015). Manuel des pratiques viticoles contre les maladies du bois, BIVC, Sicavac Centre-Loire, Imprimerie Paquereau, ISBN 978-2-37006-000-6.
  • Cholet C., Martignon T., Giudici M., Simonit M., Geny L. (2017). Vigne: pourquoi tailler moins ras aide à freiner l’esca. Phytoma hal-01603357
  • Faúndez-López P.,  Gutiérrez-Gamboa G., Moreno-Simunovic Y., (2021). The role of diaphragm as a natural resistance to the necrosis produced by pruning cuts, IVES Technical reviews, DOI: https://doi.org/10.20870/IVES-TR.2021.4817
  • McElrone A.J., Manuck C.M., Brodersen C.R., Patakas A., Pearsall K.R., Williams L.E., (2021). Functional hydraulic sectoring in grapevines as evidenced by sap flow, dye infusion, leaf removal and micro-computed tomography, AoB PLANTS, Volume 13, Issue 2, April 2021, plab003, https://doi.org/10.1093/aobpla/plab003
  • Lecomte P., Diarra B., Boisseau M., Weingartner S., Rey P., (2021). Preventing ESCA in Vitis vinifera by proscribing vine training systems or mutilating pruning methods, IVES Technical Reviews, DOI: https://ives-technicalreviews.eu/article/view/4734

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