The chain of effects between sunburn necroses and rot infestation in the context of climate change

Abstract

Climate change will increasingly challenge future viticulture due to long-enduring and extreme weather conditions, jeopardizing yield and wine quality in various ways. Elevated air temperatures, intense solar radiation and drought favour the occurrence of sunburn necroses, while high levels of precipitations lead to more severe rot infestation on grapes. Previous damages or injuries of berry skins facilitate the infection of secondary pathogens such as Botrytis cinerea, Penicillium expansum, Acetobacter spec. and wild yeasts.

In order to analyse the relationship between sunburn necroses and rot pathogens, a defoliation experiment was carried out using ‘Riesling’ as a susceptible cultivar. Bunch zones were completely defoliated on both sides of the canopy between the end of flowering and fruit set or prior to forecasted heatwaves at bunch closure and at véraison, respectively. The maximum extent of sunburn necroses was observed when defoliation was conducted at bunch closure. Conversely, the highest level of rot infestation was recorded in the non-defoliated approach. Defoliation at véraison caused a double risk to grapes leading to the second-highest severity of sunburn necroses and rot infestation, respectively. However, defoliation between the end of flowering and fruit set was able to reduce both types of damages in comparison to the respective maximum extents.

Furthermore, grape susceptibility of ‘Riesling’ and the fungus-resistant cultivar ‘Calardis Blanc’ to sunburn necroses and rot infestation was analysed. Similarly, bunch zones of the two cultivars were completely defoliated on both sides of the canopy prior to forecasted heatwaves at bunch closure over two contrasting seasons. Grapes of ‘Calardis Blanc’ were less susceptible to sunburn necroses within each year than those of ‘Riesling’. Samples of uninjured and damaged berries affected by sunburn necroses at bunch closure as well as at véraison were taken from each cultivar and inoculated with a spore suspension of B. cinerea. ‘Riesling’ berries damaged at véraison showed the highest level of B. cinerea infestation compared to the other berries of both cultivars. Additionally, ‘Riesling’ revealed a positive correlation between sunburn necroses severity of berries damaged at véraison and the resulting B. cinerea infestation. However, ‘Calardis Blanc’ was less susceptible to both, sunburn necroses as well as B. cinerea, in comparison to ‘Riesling’ and was thus able to limit this amplifying effect.