Abstract
The effect of different severities of root flooding at budbreak and 70 days after budbreak (8 to 12 leaf stage) on root and shoot growth of 'AXR#1', 'St. George', '11OR', and '420A' rootstocks was investigated. The four severities of root flooding were control (0%), 33%, 67%, and 100% of the root soil volume of each rootstock. At the budbreak stage, root and shoot growths of all rootstocks were strongly inhibited when two-thirds or more of the root soil volume was flooded. At 100% root flooding, there was no new root growth. The number of buds that sprouted and developed was unaffected by flooding. Within 10 to 15 days after flooding, the cuttings at 8 to 12 leaf stage of '420A' and '11OR' grew poorly. The color of roots exposed to 100% root flooding turned black in contrast to control plants which were mostly white. Flooding reduced the concentration of potassium and calcium in petioles of 'AXR#1' rootstocks markedly. Among the four rootstocks investigated, 'AXR #1' which was the most tolerant to flooding had the best shoot and root growths, followed by 'St. George', '110R' and'420 A'.
