Abstract
In Mediterranean-like climate areas, field-grown grapevines are typically exposed to severe environmental conditions during the summer season, which can negatively impact the sustainability of viticulture. Despite the short-term mitigation strategies available nowadays to cope with climate change, little is known regarding their effectiveness in different demarcated winegrowing regions with differing climate features. Hence, we applied a kaolin suspension (5 %) to Touriga-Franca (TF) and Touriga-Nacional (TN) grapevine varieties located in two Portuguese demarcated regions (Alentejo and Douro) with different mesoclimates to study its effect on the physiological performance, hormonal balance and ABA-related grapevine leaf gene expression during the 2017 and 2018 growing seasons. Data show that 2017 was warmer than 2018 due to the occurrence of two heatwaves in both locations, highlighting the protective effect of kaolin application under severe environmental conditions. In the first study year, at midday, kaolin enhanced water use efficiency (23 % in Douro and 13 % in Alentejo), carbon assimilation rates (PN; 72 % in Douro and 25 % in Alentejo), and the soluble sugar content of grapevine leaves, while decreasing the accumulation of plant growth regulators (ABA, IAA, and SA) during the ripening stage. The results show an up-regulation of ABA biosynthesis-related genes (VvNCED) in TF treated vines from the Douro vineyard mainly in 2017, suggesting an increased stress response under severe summer conditions. Additionally, kaolin triggered the expression of ABA-responsive genes (VvHVA22a and VvSnRK2.6) mainly in TF, indicating different varietal responses to kaolin application under fluctuating periods of summer stress.
Highlights
Viticulture is an important socioeconomic and cultural sector in many countries and regions worldwide, whose sustainability is expected to be seriously challenged by climate change in the coming years (Bernardo et al, 2018; Santos et al, 2020)
Based on the Winkler index (WI) classification regions (I–V), most of the Growing degree days (GDD) calculated fittted into region V, except for the Douro site in 2017 (2705 °C GDD), which slightly exceeded the thresholds of the warmest category (Region V: 2222-2700 °C), and was classified as “too hot” (Jones et al, 2010)
Stomatal conductance, and water use efficiency are outcomes reported in grapevines exposed to summer stress, whose efficiency has been improved by kaolin application in vineyards in the Douro region (Dinis et al, 2018b)
Summary
Viticulture is an important socioeconomic and cultural sector in many countries and regions worldwide, whose sustainability is expected to be seriously challenged by climate change in the coming years (Bernardo et al, 2018; Santos et al, 2020). Abiotic stresses trigger several plant defence responses and adaptation strategies, including osmotic and hydraulic adjustments, energy dissipation mechanisms, antioxidant defence systems, and hormonal regulation and crosstalk in complex signalling networks (Peleg and Blumwald, 2011; Bernardo et al, 2018; Balfagón et al, 2020). Antagonistic reports indicate no correlation between ABA accumulation and stomatal closure in plants subjected to combined abiotic stresses (Zandalinas et al, 2016; Balfagón et al, 2019). For example, Soar et al (2006) reported higher ABA accumulation in ‘Grenache’ leaves compared with ‘Shiraz’ under water deficit conditions, and a significant up-regulation of key genes involved in the ABA biosynthetic pathway. The regulation of many ABA-responsive genes has showed that this hormone has a key role in triggering stress adaptation responses (Wu et al, 2016; Jia et al, 2017)
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