Modelling virtual Riesling canopies for reducing sunburn risks in grapevine (Vitis vinifera L.) berries

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Sunburn in grapevine berries and other fruit crops is known as a recurring disorder causing severe yield losses and a decline in berry quality. Yet, an increased emergence of sunburn has been observed in recent years. Given that these observations of sunburn occurrence are often associated with heat waves, it is likely that there is a link between sunburn and climate change. Grapevine is an ideal model crop for studies of climate change impacts, and this is the first modelling study that aims at investigating the relevance of berry sunburn in future vineyards.Simulations of responses of vineyards to changes in environmental conditions should give us answers to the impact of climate change on sunburn. We hypothesize that future climatic conditions might affect seasonal sunburn occurrence. For example, elevated CO2 (eCO2) might reduce sunburn risks in the later season because of an increased growth of secondary lateral shoots. However, with more frequent heat waves sunburn occurrence, particularly re-lated to leaf removal, might dramatically increase. Since berry sunburn is a disorder that re-quires direct exposure of the berries to the sun, it depends on the grapevine canopy’s archi-tecture. Functional-structural plant models (FSPMs) integrate structural elements of a canopy in detail to catch the canopy’s variability. Virtual Riesling is such a FSPM for grapevine cv. Riesling. It simulates the dynamic growth of the canopy architecture within a trellis system including row orientation. Virtual Riesling has proven to be useful in assessing the significance of changing temperatures for grapevine architecture. We assume that sunburn occurrence of a grapevine berry can be predicted from three key characteristics of the berry: local sun-exposure, surface temperature and susceptibility to sunburn. All characteristics will be inte-grated in an advanced Virtual Riesling model. To this end, new models for berry and cluster growth including light sensors for berries, a model for berry sunburn, as well as an advanced three-dimensional leaf shape model will be developed and integrated. Parameterization of new sub-models and advancements of Virtual Riesling will be based on experiments con-ducted, inter alia, in a vineyard free-air carbon dioxide enrichment (FACE) facility. A series of in silico experiments will be performed to estimate the effects of morphological responses to eCO2 and increased temperature on sunburn occurrence and to identify optimized leaf re-moval practices for reducing sunburn occurrence. Finally, we will apply and compare both, standard leaf removal strategies versus the newly identified strategies theoretically favorable for reducing sunburn risks in the field.The project output will help us to better understand how climate change affects sunburn and will thus provide new ideas for mitigating effects of climate change, based on new strategies for managing plant architecture in vineyards and other agricultural systems.