Abscisic acid application regulates vascular integrity and calcium allocation within apple fruits

Abstract

Calcium is a very poorly translocated nutrient in the flesh of apple fruits with the advancement of growth. Within the fruit, movement is further restricted toward distal portion relative to proximal. Even numerous foliar applications of calcium do not always achieve the desired effect. Thus, the objective of this study was to enhance the calcium allocation in distal parts of apple fruit in response to whole plant application of abscisic acid (ABA). Five-year-old apple plants of Super Chief Sandidge on M9 were treated with ABA at 400 ppm, calcium chloride at 0.4% and water (Control) at four stages (30, 65, 100, and 135 days after full bloom (DAFB)), and then analyzed for xylem functionality and calcium allocation in leaf and various fruit tissues at 10 days after each treatment, i.e., S1—40, S2—75, S3—110, and S4—45 DAFB. The results obtained showed that xylem functionality started impairing just after S2; consequently, the calcium allocation was also reduced in middle and calyx portions of fruit after that stage. However, xylem functionality was significantly retained (up to 30%) in ABA-treated fruits at S4 stage, which in other treatments was found to be nil at the calyx end of the fruit. This retention of xylem tissue functionality enhanced allocation of calcium from roots in middle and calyx end of the apple fruit. Leaf calcium was reduced with ABA applications. With the enhancement of calcium in the fruits, increases in soluble solid content and titratable acidity were observed at maturity.