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.
- 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
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).
- 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.