Wine as G x E: effect of temperature on vine and fruit phenotype

Abstract

A production system is sustainable if it meets four conditions: it is profitable, accounts for environmental and social expectations and ensures product safety. The challenges for sustainability in the vineyard and winery overlap partially. The latest Australian Wine Industry Environment Conference highlighted four aspects relevant to sustainability: profitability, water, energy and warming climate. In this paper, we narrow our focus to warming and its implications for yield and fruit traits as drivers of profit. Sustainability challenges and opportunities have a strong regional component as the likelihood of negative (or positive) impact of warming increases (decreases) from cool to hot regions; here we concentrate on the Barossa Valley of Australia, a region with median growing season temperature of 19.0 ^oC (1970-2000). We are interested in growing grapes, making wine and selling it. Viticulture, oenology and marketing provide theories and practices to support each of these activities. The concepts of “vintage” and “terroir” are useful in marketing but unsuitable to understand grapes. A phenotype-based framework is advanced that helps to understand environmental and technological influences on vine and fruit traits relevant to wine.

The phenotype comprises all components of an organism other than its DNA. Root depth, stomatal conductance and berry anthocyanins are all aspects of the vine’s phenotype and therefore depend on the genotype (G), the environment (E) and their interaction (GxE). Vineyard management (M) can affect the phenotype directly, e.g. pruning that shapes the canopy, or indirectly through modification of the environment, e.g. irrigation that changes soil water content. Likewise, the sense of smell or her approach to wine making are aspects of the winemaker’s phenotype that result from G and E, where E is defined in the widest sense as to include personal and social history, culture, education and so forth. Wine is hence the result of two interacting phenotypes, the fruit’s and the winemaker’s; wine is GxE twice. This could be extended by making explicit the phenotypes of the microorganisms involved in winemaking, which are also the result of G, E and M and their interactions.

Ambient temperature is a component of the environment that influences vine and fruit phenotypes. Against the backdrop of climate change, we make the distinction between gradual, long-term warming at typical rates of 0.01-0.02 ^oC/yr and heat stress events. Here we summarise a 6-yr project where we compared vines exposed to elevated temperature (approx. 2^oC above ambient) with untreated controls in the Barossa Valley. The concept of phenotypic plasticity, derived from our framework, is applied to elucidate the effect of warming on juice pH and acidity. Warming was mostly neutral for yield and its effect smaller than expected for time of maturity. Elevated temperature decoupled sugars and anthocyanins in Syrah and Cabernet Franc; this was due to the shift in the onset of colouring on a TSS scale under elevated temperature. Elevated temperature also decoupled berry sensory traits. Adaptive viticultural and winemaking technologies to preserve the identity of Syrah would contribute to the sustainability of the wine sector in the Barossa Valley.