In light of the global challenges posed by recurring heat and drought episodes to sustainable grape production, a recent study conducted by Hewitt et al., published in 2023, examines the effects of these environmental stresses on wine grape varieties.
The study investigated the transcriptomic and metabolic responses of two varieties of wine grape, Cabernet Sauvignon and Riesling, to drought and heat stress. Grapevines were exposed to one of four conditions during early fruit ripening: drought stress only, heat stress only, simultaneous drought and heat stress, or no stress (control).
The researchers carried out a time-course analysis of berry metabolites, particularly organic acids, and conducted a transcriptome analysis before, during, and after the stress episode.
In contrast with previous studies on leaf response, which showed a stronger reaction to water stress, Hewitt and colleagues found that grape berries displayed a unique, organ-specific response to environmental stress. Both alone and in conjunction with water stress, heat stress had a much more significant impact on berry organic acid content, pH, and titratable acidity than water stress.
Consistent with the metabolic changes, the global transcriptomic analysis revealed that heat stress also had a more significant impact on gene expression in grape berries than water stress for both varieties. Differentially expressed genes were associated with various metabolic pathways, including the tricarboxylic acid cycle and glyoxylate cycle, mitochondrial electron transport and alternative respiration, glycolysis and gluconeogenesis, carbohydrate allocation, ascorbate metabolism, and abiotic stress signaling pathways.
These findings provide crucial knowledge regarding how environmental stresses, either independently or combined, affect the berry metabolism of different grape varieties. This will serve as the foundation for developing recommendations for climate change mitigation strategies and genetic improvement. The study suggests that with better understanding and management of heat stress, the wine industry can develop more sustainable practices in the face of climate change.
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