Grapevine cultivars are remarkably adaptable to their environments and responsive to production manipulations. This adaptability is (scientifically) described as phenotypic- or metabolic plasticity. You might not have heard these terms before, but they underpin the observation that under certain conditions the same cultivar can produce very different styles of wines, or in other words, display plasticity. To understand the plasticity of a cultivar, it is necessary to study the underlying physiology and metabolism. To do that, grapevine cultivars need to be studied in interaction with their environment (natural and manipulated). It sounds relatively easy, but it is no simple task. Considering the multitude and complexity of the individual factors potentially affecting field grown grapes, how can one reliably predict the outcome of a viticultural treatment? From a scientific perspective it comes down to the need to establish “cause-and effect” (causality) type vineyard studies. A causal relationship exists when the results/trends of an experiment are proven to be caused by the manipulation, or a specific factor. Such a study of a leaf removal treatment in a Sauvignon blanc vineyard could explain why wine style/typicity can be shifted by increased bunch exposure and provide proof of this cultivar’s metabolic plasticity.
Producers and viticulturists are confronted with a multitude of compounding factors to contend with to produce quality grapes. Some viticultural decisions are long term, and are decided during the initial establishment phase of the vineyard, and include: site selection (e.g. climate, altitude, aspect/inclination and soil), cultivar/clone selection, scion/rootstock combination, row orientation, vine/row spacing and trellising system. Needless to say, these decisions influence the ultimate quality of the grapes and are costly to change once a vineyard has been established.
Other decisions are seasonal, and can include the choice of cover crop(s), the implementation of canopy manipulations (e.g. shoot thinning, shoot trimming and leaf removal), bunch manipulations (e.g. cluster thinning), and timing of winter pruning. The grape yield and/or quality is then further influenced by the prevailing seasonal conditions (vintage) which can be considered as the sum total of all factors that the grapes are exposed to in any given season and will include wind, water (rain and/or irrigation), light, temperature, humidity and disease load (pathogens and pests). These factors do not occur in isolation, and for each of these factors both the timing and intensity is relevant. The challenge is to link these factors to outcomes in causal relationships to ultimately understand their impacts on grape/wine quality.1
We used an early leaf removal treatment in Sauvignon blanc in the moderate (cool night) region of Elgin to study the impact of increased bunch exposure on grape composition throughout berry developmental stages (i.e. green pea size through till the ripe/harvest stage).
Leaf removal is used for diverse purposes, usually with a predetermined viticultural and/or oenological outcome …