Effect of timing of irrigation initiation on vegetative growth, physiology and yield parameters in Cabernet Sauvignon grapevines

Background and Aims: The effect of the timing of the initiation of irrigation during the growing season on Vitis vinifera L. Cabernet Sauvignon vines was investigated during 5 successive years. Methods and Results: Five irrigation initiation thresholds based on measurement of midday stem water potential (Ψ_s) were examined: at Budburst, −0.6 MPa, −0.8 MPa, −1.0 MPa and − 1.2 MPa. Midday Ψ_s, gas exchange parameters [stomatal conductance (g_s) and net assimilation rate (A_n)] and leaf area index (LAI) were measured weekly. At harvest, 12 vines per replicate (48 per treatment) were separately harvested, the yield was determined and the number of bunches per vine recorded. During the winter period, the number of shoots per vine and the pruning mass of 12 vines per replicate were recorded separately. Vines in the early irrigation treatments (Budburst, −0.6 MPa) displayed improved Ψ_s, g_s and A_n, accompanied by vigorous vegetative growth and high yield. The increased yield was derived from enlarged berry size and an increased number of bunches. In contrast, vines in the late irrigation treatments (−1.0 MPa, −1.2 MPa) exhibited low Ψ_s, g_s and A_n values combined with depressed vegetative growth and reduced yield. The depression effect on late irrigation vines was cumulative and became more pronounced as trial years advanced. Our results emphasise the crucial role of water availability during springtime (vegetative growth period) on vine development, physiological performance and yield parameters. Conclusions: Early irrigation initiation during spring, in which most vegetative growth processes occur, resulted in the enhancement of all vegetative and physiological parameters. Postponing irrigation initiation, however, until advanced stages of the growing season was followed by diminished vegetative growth, reduced physiological performance and decreased yield. Significance of the Study: Our results provide insights into the effect of the timing of irrigation initiation on vegetative growth, physiological parameters and yield components in field-grown Cabernet Sauvignon grapevines.