Simulating berry sunburn with the functional–structural plant model <i>Virtual Riesling</i>

Abstract Berry sunburn in grapes is a disorder likely linked to climate change that can severely reduce yield and fruit quality. It is driven by heat impacts and requires exposure of berries to sunlight. Leaves can provide essential shading for berries, offering protection from sunburn damage. However, the inherent variability and heterogeneity of canopy architecture, in combination with different vineyard design and management strategies, influence the exposure of berries throughout the day. Studying these dynamics in the field can be challenging, particularly when considering future environmental conditions. This study aims to provide a modelling tool to simulate berry sunburn, while capturing the temporal and spatial dynamics of the heat and radiation impacts related to vineyard design and plant architecture on different days. We advanced the functional–structural grapevine model Virtual Riesling to simulate radiation environments within heterogeneous canopies related to different row orientations and weather patterns, including cluster zone leaf removal as a typical canopy management practice. The simulations highlighted the role of the course of berry shading by leaves over the day on berry sunburn for the different scenarios. Results revealed the importance of the timing of high canopy air temperatures and sunlight exposure in sunburn occurrence. Shading from surrounding leaves reduced sunburn, especially when the sun aligned with vineyard rows during azimuthal crossing. Elevated temperatures increased sunburn, but only when critical heat coincided with low shading. This study identified critical sunburn periods linked to the environment and vineyard set-up and presents a valuable tool to develop mitigation strategies in silico.