Abstract
Global warming is endangering maintenance of optimal grape composition in white varietals aimed at sparkling wine making due to difficulties to maintain adequate acidity and fresh aromas. These troubles are being faced by the main white varietal of the Colli Piacentini district, named Ortrugo. Its vegetative and reproductive behavior was compared over 3 years with that of other minor autochthonous white varietals. Criteria set for adequate grape composition under sparkling vinification (total soluble solids at 20–21°Brix) and titratable acidity (TA) ≥ 6.5 g/L combined with Principal Component Analysis (PCA) on the measured variables allowed a thinnning down of the initial group of 17 to 7 varietals including Ortrugo, Bucalò, Barbesino, Lecco, Melara, Santa Maria and Molinelli. PCA isolated Ortrugo’s behavior for inadequacy to maintain sufficient TA at harvest mostly due to extremely low malic acid concentration. However, time trend analyses of accumulation and degradation patterns of tartaric and malic acids disclosed that, in Ortrugo, the most limiting factors were more intense post-veraison tartaric acid dilution and a lower malic acid pool at veraison as compared to any other varietal. Conversely, Molinelli and Barbesino proved to be ideal material for sparkling wine purposes, as they associated to desirable agronomic features a strong ability to retain high TA with a well-balanced tartrate-to-malate ratio. Our study emphasizes that often neglected or superficially evaluated germplasm genetic resources might hide strong potential for adapting to challenges imposed by climate change in that representing an excellent tool for adaptation strategies.
Highlights
Effects of climate change on viticulture have been the object of a massive flux of scientific literature since the mid-80s’ (Mozell and Thach, 2014; Palliotti et al, 2014; Schultz, 2016; Van Leeuwen et al, 2019; De Ollas et al, 2019)
The Winkler Index (WI) calculated over a 10◦C baseline was of 2143 Degree Days (DD) which lowered to 1984 DD if the calculating period was shortened at the end of September
The 2018 season registered a higher rainfall from April to October (433 mm) than 2017; yet summer temperatures were fairly high and WI resulted in 2200 DD (2014 from April to September)
Summary
Effects of climate change on viticulture have been the object of a massive flux of scientific literature since the mid-80s’ (Mozell and Thach, 2014; Palliotti et al, 2014; Schultz, 2016; Van Leeuwen et al, 2019; De Ollas et al, 2019). If the wine target is a sparkling, a desirable grape composition at harvest is often as follows: a total soluble concentration (TSS) between 20 and 21◦Brix, a titratable acidity (TA) ≥ 6.5–7.0 g/L, a pH ≤ 3.2 and, hopefully, healthy and turgid berries. Among such desired characteristics, increased heat summations – including a marked increase of night temperatures – primarily endanger the maintenance of adequate acidity. It is well established (Ruffner, 1982; Ford, 2012) that, while tartaric acid concentration is essentially unaffected by temperature, the rapid loss in malic acid starting at the onset of berry softening is mainly temperature driven (Ford, 2012)
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