Grape cultivars adapted to hotter, drier growing regions exhibit greater photosynthesis but less negative leaf osmotic potentials under hot growing conditions

Authors: SINCLAIR, GABRIELA - University Of California, Davis; Galarneau, Erin; HNIZDOR, JOSH - University Of California, Davis; McElrone, Andrew; WALKER, ANDREW - University Of California, Davis; BARTLETT, MEGAN - University Of California, Davis

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2024
Publication Date: 3/13/2024
Citation: Sinclair, G., Galarneau, E.R., Hnizdor, J.F., McElrone, A.J., Walker, A.M., Bartlett, M.K. 2024. Grape cultivars adapted to hotter, drier growing regions exhibit greater photosynthesis but less negative leaf osmotic potentials under hot growing conditions. Annals of Botany. 134:205-217. https://doi.org/10.1093/aob/mcae032.
DOI: https://doi.org/10.1093/aob/mcae032

Interpretive Summary: Many wine-growing regions are expected to face hotter, drier growing conditions, and understanding the mechanisms grapevines use to mitigate these stresses can guide breeding programs in developing more tolerant plant material. Osmotic potential at full hydration (po) is a leaf water rleations trait strongly associated with leaf vulnerability to wilting, hydraulic dysfunction, and stomatal closure during drought. po is lower (more negative) in crop cultivars and species from drier environments, and water-stressed plants accumulate solutes in the leaf cells (i.e., osmotically adjust) to reduce po. However, po and osmotic adjustment have not been evaluated as drivers for stress tolerance across grape cultivars. We compared po, osmotic adjustment, and leaf chemical composition across 7 commercially important cultivars typically grown in regions with different climatic conditions (i.e., cool: Riesling and Pinot Noir, warm: Chardonnay, Merlot, and Syrah, and hot: Zinfandel and Sangiovese). All cultivars were established in the same experimental block in a hot (Winkler V) wine-growing region (Davis, California) and measured over the hottest, driest period of the growing season (from veraison to harvest). As hypothesized, 'o varied significantly between cultivars, and all cultivars significantly reduced 'o (osmotically adjusted) over the study period. 'o was correlated with cultivar climate associations and with gas exchange parameters early in the season but opposite of expected. For example, Pi o was less negative in cultivars associated with hotter, less humid growing regions and stomatal conductance and photosynthesis were higher in cultivars with less negative. Leaf K, Ca, and Mg contents varied between cultivars and these ion and total amino acid contents changed over the study period, but this variation was not related to cultivar climate associations. Overall, these findings suggest that developing a heat-tolerant photosynthetic biochemistry has been a more important mechanism adapting winegrapes to hotter, drier conditions than improving leaf drought tolerance through lower osmotic potentials or greater osmotic adjustment.

Technical Abstract: Many wine-growing regions are expected to face hotter, drier growing conditions, and understanding the mechanisms grapevines use to mitigate these stresses can guide breeding programs in developing more tolerant plant material. Osmotic potential at full hydration (po) is a leaf water rleations trait strongly associated with leaf vulnerability to wilting, hydraulic dysfunction, and stomatal closure during drought. po is lower (more negative) in crop cultivars and species from drier environments, and water-stressed plants accumulate solutes in the leaf cells (i.e., osmotically adjust) to reduce po. However, po and osmotic adjustment have not been evaluated as drivers for stress tolerance across grape cultivars. We compared po, osmotic adjustment, and leaf chemical composition across 7 commercially important cultivars typically grown in regions with different climatic conditions (i.e., cool: Riesling and Pinot Noir, warm: Chardonnay, Merlot, and Syrah, and hot: Zinfandel and Sangiovese). All cultivars were established in the same experimental block in a hot (Winkler V) wine-growing region (Davis, California) and measured over the hottest, driest period of the growing season (from veraison to harvest). As hypothesized, 'o varied significantly between cultivars, and all cultivars significantly reduced 'o (osmotically adjusted) over the study period. 'o was correlated with cultivar climate associations and with gas exchange parameters early in the season but opposite of expected. For example, Pi o was less negative in cultivars associated with hotter, less humid growing regions and stomatal conductance and photosynthesis were higher in cultivars with less negative. Leaf K, Ca, and Mg contents varied between cultivars and these ion and total amino acid contents changed over the study period, but this variation was not related to cultivar climate associations. Overall, these findings suggest that developing a heat-tolerant photosynthetic biochemistry has been a more important mechanism adapting winegrapes to hotter, drier conditions than improving leaf drought tolerance through lower osmotic potentials or greater osmotic adjustment.