Stomatal Sensitivity of Grapevine Varieties Relates to Changes to Berry Growth and ABA During Water Deficit.

Stomatal sensitivity of grapevine varieties has been largely investigated to better understand differences among varieties in water deficit (WD) tolerance. Grapevine varieties also exhibit distinct berry growth and ripening responses under WD, but whether the nature and magnitude of these responses can be predicted by stomatal sensitivity remains unresolved. We tested whether varietal differences in berry responses are linked to stomatal regulation, and whether these relationships depend on WD timing and dynamics. Short-term severe deficit (STSD) and long-term maintained deficit (LTMD) were applied before (pre-veraison) and after (post-veraison) the onset of berry ripening to four grapevine varieties. Vine physiology, leaf and berry abscisic acid (ABA), and berry growth and composition were tracked throughout the experiments. Under STSD, varieties exhibiting earlier stomatal closure showed greater reductions in berry size (at pre-veraison) and larger increases in ABA, whereas changes in sugars were generally unrelated to stomatal behaviour. In contrast, LTMD induced weaker and less consistent effects on berry size and metabolites, with ABA remaining the only response that consistently reflected varietal differences in stomatal regulation. These results suggest that stomatal regulation primarily influences berry growth and ABA during drought, while berry sugar and acid levels are largely independent of variety-specific stomatal responses.