Decoding Heat-Shock Responses in <i>Vitis vinifera</i> L. by Metabolic, VOC, and Physiological Profiling: Toward the Identification of Volatile and Metabolic Biomarkers

Grapevine (<i>Vitis</i> spp.) is a crop of major economic importance in Europe. Rising temperatures and extreme weather events reduce the yield and alter berry composition, affecting wine quality. Despite advances in vineyard management, mechanisms underlying grapevine thermotolerance remain poorly understood. To fill this gap, we combined physiological and volatile organic compound profiling and untargeted metabolomics. Selected genotypes from a 'Rhine Riesling' × 'Cabernet Sauvignon' progeny were exposed to a 3 h heat shock at 40 and 43 °C under controlled conditions. At 43 °C, genotypes were heat stressed, with a significant chlorophyll fluorescence decrease and modulation of leaf transpiration and metabolism. VOC analysis highlighted 6-methyl-5-hepten-2-one as a candidate heat stress marker, as well as benzenic compounds (i.e., 2-phenyl-2-propanol). Untargeted metabolite profiling revealed several candidate heat-stress biomarkers; notably, the hypothesized 2-<i>C</i>-methyl-d-erythritol 2,4-cyclodiphosphate (MEP-cPP) and guanosine accumulated preferentially in susceptible genotypes. Both markers were validated in the field, providing candidate molecular tools for breeding heat-tolerant grapevines.