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American Society for Horticultural Science






American Society for Horticultural Science

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The Gisela® series of dwarfing rootstock are widely used because they enable high-density production, but they may be sensitive to drought. Drought tolerance may be associated with root-zone distribution and depth or with physiological adaptation to low water potential. Here we describe a novel technique for determining physiological tolerance to drought when root distribution is held constant. In two matching studies, we continuously measured transpiration of two groups of eight trees using a 16-container automated weighing lysimeter system in a greenhouse. With this system, Gisela® 3, 5, and 12 (G.3, G.5, and G.12) rootstocks were subjected to multiple, controlled drought cycles based on reductions in whole-tree transpiration. To provide an equivalent amount of stress for each tree, water was withheld until the daily transpiration rate had decreased to less than 250 g of water transpired per tree per day. Each tree was then drip-irrigated to bring the root-zone back to about field capacity. G.3 and G.12 rootstocks more rapidly recovered to maximum transpiration rates compared with G.5 (an indication of ability to resume normal growth after a drought). At harvest, G.3 and G.12 rootstocks also had greater leaf area and trunk diameter. Both transpiration data and harvest data indicate physiological differences among rootstocks. Because root-zone volume was constant, these differences are not associated with changes in root distribution or depth. These data indicate that G.5 is less adapted for regulated deficit irrigation strategies that include long irrigation intervals.