Resilience of grapevine berries to sunburn necrosis and secondary infections

Abstract

Climate change increasingly challenges viticulture through heatwaves and drought on the one hand as well as high precipitation levels on the other. Several conventional cultivars are thus affected by damage to grapes such as sunburn necrosis and rot infestation, which can severely impair yield and wine quality. While grapevine breeding has traditionally focused on resilience to biotic stress, tolerance to abiotic stress is becoming equally important. In this context, the identification of stress-resilient traits is essential for modern breeding strategies.

The conventional cultivar ‘Riesling’ and the genetically related, fungus-resistant cultivar ‘Calardis Blanc’ were selected to investigate grape susceptibility to sunburn necrosis and its influence on secondary infections by Botrytis cinerea. In order to determine the extent of sunburn necrosis, bunch zones of the cultivars were completely defoliated on both sides of the canopy from bunch closure onwards, prior to the respective heatwave events. At harvest, berries without visible injuries as well as berries affected by sunburn necrosis at bunch closure or at véraison were selected, inoculated with a B. cinerea spore suspension and incubated for a minimum of three weeks. The extent of sunburn necrosis on grapes and B. cinerea on berries was assessed for each cultivar across two growing seasons.

‘Riesling’ exhibited a higher severity of sunburn necrosis than ‘Calardis Blanc’, although the extent varied between years. Uninjured berries of both cultivars showed no differences in susceptibility to B. cinerea. In contrast, berries damaged at véraison revealed a markedly higher level of B. cinerea infestation in ‘Riesling’ compared to ‘Calardis Blanc’. Sunburn necrosis occurring at bunch closure did not promote secondary infections in ‘Riesling’, likely due to the smaller size and higher firmness of sunburn damages on berry skin. The differences between cultivars were not attributed to the sugar content of the berries. Previous studies have shown that ‘Calardis Blanc’ is characterised by a looser grape architecture and an increased firmness of berry skin compared to ‘Riesling’, which could prevent B. cinerea infections. Moreover, the antioxidative capacity of berries may contribute to differences in the resilience to sunburn necrosis between cultivars.

The results suggest that grape architecture and berry skin thickness display promising traits for breeding programs, which aim at improving grapevine adaptation to abiotic and biotic stress under future climatic conditions.