WATER RELATIONS AND PHOTOSYNTHETIC RESPONSES OF TWO GRAPEVINE CULTIVARS OF DIFFERENT GEOGRAPHICAL ORIGIN DURING WATER STRESS

A comparative study on adaptive responses to water deficit was conducted on 8-year old vines of the cultivars Grenache, of Mediterranean origin, and Syrah of mesic origin, grown side by side in a commercial vineyard near Montpellier, France.
Maximum stomatal conductance (g_max) and maximum photosynthesis (A_max) of Grenache were more sensitive to water deficit (expressed as pre-dawn leaf water potential, _PD) than g_max and A_max of Syrah.
Intrinsic water use efficiency (A/g) increased with decreasing _PD but more so for Grenache than Syrah.
Water stressed Syrah vines matured fruit to similar sugar concentration and colour densities than the irrigated control, despite reaching _PD‘S of up to -1.4 MPa.
Unirrigated Grenache vines failed to ripen fruit adequately, yet reached only minimal _PD values of -0.85 MPa.
Measurements of chlorophyll fluorescence indicated a pronounced down-regulation of photosystem II (PSII) activity under high light at high leaf temperatures during the water stress for Grenache but not for Syrah.
Leaf water potential isotherms showed that Syrah had a higher leaf elasticity, lower turgid to dry weight ratio, and lower osmotic potential than Grenache.
Therefore, turgor loss occurred at lower relative water contents in Syrah, which may allow this cultivar to maintain stomatal opening at lower water potentials and to better exploit the soil water reserves.

Strategies to Optimize Wine Grape Quality

H.R. Schultz

gas-exchange, water potential, turgor, chlorophyll fluorescence, stomatal opening

https://doi.org/10.17660/ActaHortic.1996.427.30