Influence of Foliar Kaolin Application and Irrigation on Photosynthetic Activity of Grape Berries

Abstract

Climate changes may cause severe impacts both on grapevine and berry development. Foliar application of kaolin has been suggested as a mitigation strategy to cope with stress caused by excessive heat/radiation absorbed by leaves and grape berry clusters. However, its effect on the light micro-environment inside the canopy and clusters, as well as on the acclimation status and physiological responses of the grape berries, is unclear. The main objective of this work was to evaluate the effect of foliar kaolin application on the photosynthetic activity of the exocarp and seeds, which are the main photosynthetically active berry tissues. For this purpose, berries from high light (HL) and low light (LL) microclimates in the canopy, from kaolin-treated and non-treated, irrigated and non-irrigated plants, were collected at three developmental stages. Photochemical and non-photochemical efficiencies of both tissues were obtained by a pulse amplitude modulated chlorophyll fluorescence imaging analysis. The maximum quantum efficiency (Fv/Fm) data for green HL-grown berries suggest that kaolin application can protect the berry exocarp from light stress. At the mature stage, exocarps of LL grapes from irrigated plants treated with kaolin presented higher Fv/Fm and relative electron transport rates (rETR200) than those without kaolin. However, for the seeds, a negative interaction between kaolin and irrigation were observed especially in HL grapes. These results highlight the impact of foliar kaolin application on the photosynthetic performance of grape berries growing under different light microclimates and irrigation regimes, throughout the season. This provides insights for a more case-oriented application of this mitigation strategy on grapevines.

Metabolomics of Photosynthetically Active Tissues in White Grapes: Effects of Light Microclimate and Stress Mitigation Strategies

“…Kaolin, Al 2 Si 2 O 5 (OH) 4 , is a white inert clay mineral that reflects solar radiation. Not only does it reflect damaging ultraviolet (UV) and heat-generating infrared radiation (IR), but also photosynthetically active radiation (PAR) in a less significant manner [ 18 ]. Previous works demonstrated the beneficial effects of kaolin on both grapevine leaves, like a decrease in leaf temperature at midday with a parallel increase in both photosynthetic efficiency and photoassimilate synthesis [ 17 , 19 , 20 ], and the biochemical composition of the berries, including an increase in phenylpropanoids and flavonoids [ 21 , 22 ].…”

“…Light is a key factor in the physiology of the plant, enabling photosynthesis [ 18 , 23 ] and related processes, including shoot development and biosynthesis of an array of primary and secondary metabolites [ 24 , 25 , 26 ]. In fact, photosynthesis is not exclusive to leaves, but it can also occur in other green tissues including reproductive organs like fruits and seeds [ 27 ].…”

“…In fact, photosynthesis is not exclusive to leaves, but it can also occur in other green tissues including reproductive organs like fruits and seeds [ 27 ]. We previously characterized the photosynthetic activity of the two most photosynthetic competent grapevine fruit tissues, the exocarp (skin) and seed integuments [ 28 ], and of berries growing at contrasting light microclimates that naturally occur inside the plant canopy [ 18 , 23 ]. The so-called Low Light (LL) grape berry clusters grow in the shaded inner zones of the canopy, where they are exposed to only diffuse, reflected and transmitted light and lower temperatures (approx.…”

“…50 μmol photons m −2 s −1 and a temperature of 26 °C), while the High Light (HL) clusters are exposed to both more direct or reflected sunlight and higher temperatures for the greatest part of the day (approx. 150 μmol photons m −2 s −1 and a temperature of 30 °C) [ 18 ]. Overall, our previous studies showed that the exocarp and seeds from HL berries exhibited a significantly higher photosynthetic capacity than the LL berries, especially at their green stage [ 18 , 23 ].…”

Viticulture and Winemaking under Climate Change

“…Additionally, another study makes use of reflectance indices to assess vine water status [21]. Other articles are devoted to new and innovative management practices that could prove beneficial under future climates, such as the semi-minimal pruned hedge [22], the application of kaolin clay [23], or even the introduction of unmanned aerial vehicles in vineyards to assess climate change impacts [24]. There are studies devoted to understanding the adaptation potential of some grapevine varieties under the context of climate change [25][26][27], while another article studies the effect of future enhanced CO 2 levels on specific vine pests.…”