Influence of thermal stress on Malbec, Syrah, and Bonarda (Vitis vinifera L.) anthocyanin content and evolution in growing seasons with heatwaves in semi-arid climate (Argentina)

Abstract

It is known that high temperature influences the synthesis, transformation and degradation of grape anthocyanin (ANT) threatening the quality of grapes and coloured wines. The increasing temperature, due to climate change, is expected to negatively influence the metabolism of ANT. Moreover, heatwaves that are related to global warming are growing in length and frequency worldwide, exacerbating the thermal stress on plants. Specifically, in the semi-arid condition of Mendoza viticultural area, heatwaves have been intensifying, giving opportunity to study in depth the effect of the thermal stress on ANT accumulation during growing seasons. The aims of this biannual study on three varieties were: i) evaluating the relationship between thermal accumulation and the ANT seasonal dynamic; ii) evaluating whether an evaporative cooling treatment over the canopy may alleviate the impact of the thermal accumulation during heatwaves on ANT; iii) identifying if any thermal indexes can be related to ANT profile and concentration helping growers to adapt the vineyard management preventing grape damage.

During heatwaves, the vine canopy of three cultivars (Malbec, Bonarda and Syrah) were treated in an experimental vineyard, with the Overhead Spray Water Treatment (OSWT) in two growing seasons. Within the canopy iButton sensors were used to record the temperature. Two (2 and 8 day-length) and one (10 day-length) heatwaves were identified in the two growing seasons, respectively. Four to six berry samples were collected from veraison to harvest to assess soluble solid content and ANT concentration and profile. From the beginning of veraison to the date of each sampling, thermal accumulation indexes were calculated. ANOVA and PCA were carried out.

The OSWT lowered canopy and berry temperature, modified ANT profile by decreasing their acylation, without changing the total concentration. Treatments and cultivars were differentiated by the calculated thermal indexes on the basis of ANT concentration and/or profile. In the presence of thermal excesses, plant management can include systems for temperature control at microscale level. Among these, the OWST, tested in this study, showed reproducible impact over the years, together with an effect on the ANT profile. The technique can be of valuable help in different circumstances but its application must depend on the oenological aims. Other aspects still under analysis will be discussed.