Identifying best parameters to characterize genotypes capability of retaining adequate malic acid at harvest and in final wines

Introduction

Under current climate change pressures, obtaining grapes with adequate acidity at harvest is one of the main challenges for growers, especially if the goal is producing sparkling wines. This issue arises from two main occurrences: i) higher temperatures enhance degradation of malic acid; ii) grape maturity may occur under suboptimal climatic conditions due to an advanced phenology (Palliotti et al. 2014). For this reason, the introduction of new varieties or the reconsideration of minor and insofar neglected cultivars or clones are gaining enormous interest and popularity (Palliotti et al. 2014, Poni et al. 2020, Antolìn et al. 2020). However, criteria for the identification of performing genotypes in terms of ‘acidity at harvest’ are complex. Late veraison and ripening can be inappropriate traits, since they do not necessarily mean that grapes maintain adequate acidity in relation to a satisfying sugars concentration (Palliotti et al. 2014, Frioni et al. 2020). Considering the evolution and the destination of organic acids in grapes, pre-veraison malic acid pool could represent a promising trait. In the same framework, an eventual genetic control over malic acid degradation rates could lead to different conclusions. The same can be said for the ratio between minimum acidity and starting malate abundancy, or for sugars/acidity ratio. However, any of the above-mentioned parameters seems to underestimate some of the factors involved, or in any case to provide an incomplete overview of grapes ripening.