Sunburn in Grapes: A Review.

Joanna M Gambetta,Manfred Stoll,Matthias Friedel,Bruno P Holzapfel

doi:10.3389/fpls.2020.604691

Joanna M Gambetta, Manfred Stoll + Show 2 more

Open Access

https://doi.org/10.3389/fpls.2020.604691

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Abstract

Sunburn is a physiological disorder that affects the visual and organoleptic properties of grapes. The appearance of brown and necrotic spots severely affects the commercial value of the fruit, and in extreme cases, significantly decreases yield. Depending on the severity of the damage and the driving factors, sunburn on grapes can be classified as sunburn browning (SB) or as sunburn necrosis (SN). Sunburn results from a combination of excessive photosynthetically active radiation (PAR) and UV radiation and temperature that can be exacerbated by other stress factors such as water deficit. Fruit respond to these by activating antioxidant defense mechanisms, de novo synthesis of optical screening compounds and heat-shock proteins as well as through morphological adaptation. This review summarizes the current knowledge on sunburn in grapes and compares it with relevant literature on other fruits. It also discusses the different factors affecting the appearance and degree of sunburn, as well as the biochemical response of grapes to this phenomenon and different potential mitigation strategies. This review proposes further directions for research into sunburn in grapes.

Highlights

Sunburn occurs in the field as the result of a combination of high-light intensities, high temperature, and UV radiation (Rustioni et al, 2014)
Sunburn is mainly a consequence of photooxidative damage that is exacerbated by thermal stress
When faced with light and/or heat stress, the berry activates a cascade of reactions aimed at protecting its photosynthetic apparatus by compensating the accumulation of toxic ROS species

Summary

Introduction

Sunburn occurs in the field as the result of a combination of high-light intensities, high temperature, and UV radiation (Rustioni et al, 2014). Sunburn represents a serious defect in table grapes, as browning strongly decreases the market value of the crop (United States Department of Agriculture, 1999; Suehiro et al, 2014), and causes significant losses in quality and yield of wine grapes (Figure 1). In Australia, sunburn affects 5–15% of the total wine grape production (Greer et al, 2006), and observations in Chile indicate that up to 40% of bunches can show sunburn damage in sensitive varieties like Muscat (Calderon-Orellana et al, 2018). In other crops such as blueberries (10% value loss in both Washington and Oregon in 2015; Yang et al, 2019), apples

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