Early Measures of Drought Tolerance in Four Grape Rootstocks

Recent and severe droughts in major grape (Vitis)-growing regions of the United States and Australia underscore the importance of more efficient agricultural use of water. Grape rootstock breeding for increased drought tolerance could contribute to continued sustainable yields as fresh water supplies decline. Rhizotron containers were used in a greenhouse to investigate the predictive measures of drought tolerance in young grapevine rootstocks. Deeper rooting distributions were found for the drought-tolerant rootstocks '110R' (Vitis berlandieri × Vitis rupestris) and 'Ramsey' (Vitis champinii, a natural hybrid of Vitis candicans × V. rupestris) as opposed to shallower distributions observed in the more drought-sensitive rootstocks '101-14Mgt' (Vitis riparia × V. rupestris) and 'Riparia Gloire' (V. riparia). Production of new roots during a 6-day nonirrigated period declined 45% to 53% for 'Riparia Gloire' and '101-14Mgt', respectively, but showed no change in '110R' and 'Ramsey'. Slow growth, a hallmark of abiotic stress tolerance, was evident in the drought-tolerant rootstocks in their relatively slow shoot growth before drought stress and their relatively slow new root growth during recovery, especially for 'Ramsey'. High stomatal conductance (gS) corresponded with drought tolerance and distinguished rootstocks best during the first 3 days of recovery, with a mean value for 'Ramsey' 2.7 times higher than '101-14Mgt'. Stomatal conductance during recovery may serve as the most efficient means of predicting drought tolerance capacity in a breeding program