The use of water potentials in irrigation management of table grape grown under semiarid climate in Tunisia

Aim: To evaluate the usability of various plant water potentials in table grape irrigation management under a semiarid climate.Methods and results: Two water regimes were set up. The « control » water regime was the one usually used in the vineyard. The « 50 % Irrigation » water regime delivered only half the quantity of water to the vines. Predawn leaf (ψ L PD), predawn stem (ψ S PD), midday leaf (ψ L M), and midday stem (ψ S M) water potentials were measured during the growing season. The results show that the four water potentials can accurately measure the vine water status in table grape vineyard at a daily and seasonal time scale. But, ψ L M appeared to be the most reliable indicator to differentiate between the two water regimes with a frequency of 73 %. The « 50 % Irrigation » water regime induced in the ‘Italia’ cultivar an anisohydric behavior and a decrease of 29.4 % in vine vigor and 11.5 % in berry weight. Under the Tunisian climate, ‘Italia’ cultivar may exhibit night time transpiration that decreases ψ L PD by 19.5 %.Conclusion: Preliminary minimum ψ L M threshold to produce high quality table grape would be -0.8 and -1.1 MPa for pre- and post-veraison, respectively.Significance and impact of the study: The pressure chamber is an effective device for irrigation management in commercial table grape vineyards under semiarid conditions.