Coping with extreme climatic events: some lessons from recent work on grapevine under heat peak

Questo simposio organizzato dall ‘Associazione nazionale Città del Vino, che mi onoro di presiedere, è per me motivo di particolare soddisfazione perché porta a compimento parte di un percorso iniziato dall’associazione da alcuni anni e che ha un obiettivo apparentemente semplice: sollecitare gli amministratori delle Città del Vino a perseguire con tenacia, tal­volta anche con la necessaria caparbietà, programmi ed interventi che abbiano al centro, sempre, la qualità della vita dei loro territori.

The quality of bottled white wines is highly influenced by their storage conditions, mainly temperature, and exposure to light and oxygen (1, 2).

The interest in sustainable and ecologic agricultural practices in grapevine has grown significantly in recent years in the context of ecological transition. Organic mulches are treatments that support the circular economy and positively affect the soil and the plant. They are an alternative to herbicides and other conventional practices since they may influence soil moisture, erosion, structure and weed control. However, their effects on the soil and must microbiota remain unknown.

Consumers’ demand for non-alcoholic wine has notably increased in the last years: this trend is a consequence of a growing interest in more healthy habits, and as a response to higher alcohol levels in wine due to climate change. In addition, drinking limitations due to physiological/pathological conditions (e.g., pregnancy, diabetes, hepatic disorders), driving regulations, ethical/religious considerations, and high import taxes on alcoholic beverages have positively influenced this marked (us$ 1.6 billion in 2021). International organisation of vine and wine (OIV) established that alcohol content defining wines must not be less than 8.5% vol, (OIV, 2017).

Water status impact in viticulture has been widely explored, as it strongly affects grapevine physiology and grape chemical composition. It is considered as a key component of vitivinicultural terroir. Most of the studies concerning grapevine water status have focused on either physiological traits, or berry compounds, or traits involved in wine quality. Here, the response of grapevine to water availability during the ripening period is assessed through non-targeted metabolomics analysis of grape berries by ultra-high resolution mass spectrometry. The grapevine water status has been assessed during 2 consecutive years (2019 & 2020), through carbon isotope discrimination on juices from berries collected at maturity (21.5 brix approx.) for 2 Vitis vinifera cv. Pinot noir (PN) and Chardonnay (CH). A total of 220 grape juices were collected from 5 countries worldwide (Italy; Argentina; France; Germany; Portugal). Measured δ13C (‰) varied from -28.73 to -22.6 for PN, and from -28.79 to -21.67 for CH. These results also clearly revealed higher water stress for the 2020 vintage. The same grape juices have been analysed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) and Liquid Chromatography coupled to Mass Spectrometry (LC-qTOF-MS), leading to the detection of up to 4500 CHONS containing elemental compositions, and thus likely tens of thousands of individual compounds, which include fatty acids, organic acids, peptides, phenolics, also with high levels of glycosylation. Multivariate statistical analysis revealed that up to 160 elemental compositions, covering the whole range of detected masses (100 –1000 m/z), were significantly correlated to the observed gradients of water status. Examples of chemical markers, which are representative of these complex fingerprints, include various derivatives of the known abscisic acid (ABA), such as phaesic acid or abscisic acid glucose ester, which are significantly correlated with higher water stress, regardless of the variety. Cultivar-specific behaviours could also be identified from these fingerprints. Our results provide an unprecedented representation of the metabolic diversity, which is involved in the water status regulation at the grape level, and which could contribute to a better knowledge of the grapevine mitigation strategy in a climate change context.