Assessing winegrape suitability in a changing climate through phenology and thermal physiology

There is a pressing need for cost-efficient adaptation of agriculture to a warming climate. An increasingly supported approach relies on leveraging varietal diversity, assuming that crop varieties exhibit distinct responses to climate, thereby providing a range of choices under various scenarios. This holds true for winegrapes, where considerable variability in phenological and physiological traits has been documented across varieties. However, it remains unclear whether phenology or physiology is more informative concerning varietal suitability to diverse climate conditions. Additionally, the extent to which phenology and physiology correlate in a predictable manner is still unknown, raising the question of whether one can be utilized as a surrogate of the other. In this study, we address these questions by examining understudied varieties of Iberian winegrapes as a case study. We integrate field phenological observations from the last decades with results from experiments determining the heat tolerance of eight varieties of Spanish and Portuguese winegrapes. Our findings reveal that there is no unequivocal relationship between phenology and thermal physiology. Specifically, later varieties, assumed to better cope with warming climates, do not consistently exhibit greater heat tolerance. These results suggest that phenology and heat tolerance are not interchangeable but instead represent complementary sources of information. Consequently, they can (and should) be integrated into assessments of the risk of thermal stress and climate suitability of winegrape varieties.