The latest trends in vineyard and wine research

Fruition Sciences attended the Giesco conference, which took place in Gruissan and Montpellier, France between May 31st and June 5th. The Giesco is an international group of experts in viticulture who discuss findings about the newest trends in vineyard research and their consequences on fruit and wine composition. Because the group involves researchers, vineyard owners, vineyard managers and winemakers from all over the world, it focuses on vine performances under very contrasted climates and growing conditions (from tropical climates of Brazil to the coolest wine regions of Poland or Canada). Fruition contributed to the Giesco because we believe that the practical implications from recent results will shape new practices and drive improvements in precision viticulture and ultimately will directly impact wine production. In this post, we present some key ideas exposed during the symposium,, which have sparked our attention. Because of the density and quality of the findings that have been discussed, only a part of the results are presented below.

Vine water use, biomass synthesis, and yield variations in the context of climatic changes

Hofmann et al. (Geisenheim Univ., Germany) discussed how climatic demand varies with the steepness of vineyard slope angle. Keller et al, (Washington S.U., USA) investigated the relationships between irrigation, vine transpiration and berry response in terms of sugar flow and size variations. Their results shed light on why withholding irrigation after veraison can lead to berry shrinkage and yield loss.

Delpuech et al. (IFV, France) evaluated the extent to which irrigation and fertilization can offset permanent cover crop competition in a semi-arid vineyard for yield management. Their results highlighted the benefits of using vine water deficit indexes to account for the effects of current and previous year Nitrogen and water deficits on vine production. Scholasch et al. (Fruition Sciences) showed how the measurement of a continuous vine water deficit index leads to significant water savings (> 60%) while improving yield and fruit composition during the 2014 California drought.
As rain distribution becomes more erratic and water scarcity increases worldwide, impact of water availability on leaf area development is studied under different climates. V. Pagay et al. (Adelaide Univ., Australia) discussed shoot length management according to shoot growth responses to soil moisture deficits under cool climates. Shoot vulnerability to water deficit varies with shoot length, which has direct applications for shoot thinning and irrigation practices. To better understand how water is being conducted through the shoot, particularly under drier climate, Petoumenou et al. (Univ. of Thessaly, Greece) have analyzed xylem vessels size and distribution in Syrah. Their observations regarding xylem diameter variations in response to contrasted irrigation regimes have direct applications for water management best practices. In particular, it provides guidelines on how to shape the vine “water piping system” to make the vineyard more resistant to drought.
Ledru-Coupel et al. (Supagro, Montpellier, France) analyzed variations in night time transpiration. Their results show that night time transpiration represents 10 % to 30% of day time losses and varies extremely between varietals. These observations challenge that it is possible to evaluate soil moisture availability through leaf water potential measurement. Results suggest that irrigation strategies based on leaf water potential should be revisited to improve vine water management practices. The 2 key findings here are that:
  • Night time water losses are not accounted for by vine water balance models, which affects the ability to simulate leaf water potential variations.
  • Pre-dawn LWP does not always equilibrate with soil moisture content if plant never stops transpiring at night. In this situation, LWP readings suggest that there is less water available than the plant really sees after a full night of transpiration.

New technologies and measurement tool to monitor berry compounds

During berry development, flavonoids dynamics depend upon fruit microclimate. Thus, relationships between berry composition, light and temperature is investigated, particularly under warmer climates. Those results have direct implications on wine production since optimizing fruit phenolic composition is critical to wine quality. Focusing on Syrah, Lebon et al. (Supagro, Montpellier, France) showed that exposure to sunlight is associated with higher anthocyanins accumulation up to the point where excess heat causes berry temperature to become detrimental. Beyond that point, additional heating results in significant reduction in anthocyanins content for shaded and west exposed clusters. Their results highlight the complex combined effect of light and temperature on flavonols and anthocyanins berry composition.
Lafontaine et al. (Geisenheim Univ., Germany) have used a non-invasive fluorescence method (Bacchimeter) with Pinot Noir over contrasted vintages to evaluate the correlation between bacchimeter signals and anthocyanins concentration. Results showed that the correlation was stable over 4 vintages proving that calibration of bacchimeter against anthocyanins is not required every year. Allamy et al. (Château Latour, France – Bordeaux Univ.) studied the effect of harvest date on the aromas of Merlot and Cabernet Sauvignon must and wines. Two odoriferous compounds were identified (furaneol and nonalactone), which are related to harvest date. Different harvest dates did not affect levels of compounds in the must but affected levels of volatile compounds in the wine. Results shows that a 4 days period is enough to change concentration in wine.

Management Techniques comparison: Biodynamics, Organic, Conventional

Over several consecutive vintages, Collins et al. (Adelaide Univ., Australia) compared vineyard performances from a plant, fruit and wine standpoint. Results show that with organic and biodynamics treatment:

  • soil properties improve (total organic carbon, microbial biomass, phosphorous levels increase),
  • vine production is lower (less pruning weight and less yield),
  • but yield/pruning weight ratio and petioles levels are maintained.

No consistent results regarding wine and fruit composition were found after chemical analysis (phenolics, Anthocyanins, Brix, pH, TA, YAN). However, blind tasting reveals that wine experts score organic and biodynamics wines higher. Consequently very few differences are found according to traditional measures of wine and fruit “quality” whereas sensory differences are consistently found by “experts” panels. Findings suggests that we are not measuring the right quality traits. Last, from an economical standpoint, organic and biodynamics treatments reduce income by 25% (due to additional cost of cultivation + yield loss).

A similar study was performed in Germany. By comparing integrated, organic and biodynamic viticulture, Doring et al. (Geisenheim Univ., Germany) shows that under organic and biodynamic treatments, vine production is characterized by a:
  • higher Nitrogen content (soil and leaf tissue),
  • higher total soluble solids at harvest,
  • lower growth (pruning weight, internode length, primary shoots),
  • lower chlorophyll content in leaves,
  • lower cluster weight.

The study highlights some practical “take home” for organic and biodynamics growers:

  • Minimize cover crop water use after full bloom (otherwise berry size decreases, leading to yield reduction).
  • Enhance chlorophyll content and plant physiological performances (by monitoring Magnesium supply).

Perspectives on vineyard performance variations

The traditional perception is that “weak” vines, with less pruning weight, experience more water deficit while “vigorous” vines, with more pruning weight, experience less water deficit. In fact the situation is more complex. Vasconcelos et al. (Eastern Institute of Technology, Napier, New Zealand) studied rootstock-scion interactions to better understand their impact on water status and canopy development. She distinguished very contrasted interactions and some of them are counter-intuitive.

In one hand, a combination rootstock-scion can be “optimistic” meaning that a lot of biomass is produced, but later during the season,  the stem water potential will reach very negative values. The water deficit will be more severe on more vigorous vines. On the other hand, a combination rootstock-scion can be “pessimistic” meaning that a smaller amount of biomass is produced, and the vine looks “weaker”. However,  the early reduction in biomass is associated with stem water potential values that are less negative during the season. It is as if the vine adopted early a “worst case scenario” strategy to cope with a drought expected to happen in the future. The water deficit will be less severe on weaker vines. Such results challenge our perception of water stress according to vine vigor.

Marguerit et al. (Bordeaux Sciences Agro, France) studied water use efficiency and biomass accumulation for Cabernet Sauvignon scions grafted on different rootstocks. Results show that water deficit tolerance is independent from rootstock effect on vegetative expression. Thus, the genetic determinism of these two traits is partially independent. This directly impact rootstock selection pre planting.

Smart (Smart Viticulture, Newlyn, UK) shared his concerns regarding the world wide spread of Grapevine trunk diseases, which are a bigger threat than Phylloxera. “How many growers have grapevine trunk disease in their vineyards?”
Schultz (Geisenheim, Germany) stresses the impact of global warming on rising soil temperature. At 1 meter depth, over one century a rise of 2.5 to 3.2 Celsius has been measured. Rising soil temperature means faster soil water loss, increased soil respiration which in turn increases CO2 release from the soil, faster organic matter degradation. Together with changes in precipitation patterns, this will cause sudden “spurts” of Nitrogen to be released. What will be their effects on vine performances?
Posted by Vintage Report

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