Does dye infusion indicate xylem functionality in kiwifruit?

This study was undertaken to establish whether the rate of uptake of an aqueous solution by the fruitstalks of detached Actinidia deliciosa fruits (‘Hayward’) correlates with fruit xylem functionality assessed by dye infusion. Fruits were collected from the orchard, pre-dawn and 65 days after bloom. In the laboratory the fruitstalks were re-cut under water and their outsides lightly smeared with Vaseline before placing their cut ends in small, pre-weighed (W1) (mg) vials of dye solution. Fruits were allowed to take up dye solution for ~100 min (T) under uniform aerial conditions. Fruits were then sliced 1/5 way up from the stalk end and the fraction (F) (%) of stained bundles was determined. The residual dye solution was weighed (W2) (mg) and the solution uptake rate (U) (mg/min) determined per unit of fruit surface area (S) as U=(W1-W2)/(S×T). Analysis reveals that F is linearly related to U (R2 = 0.81). The suitability of the stain infusion technique for assessing xylem functionality is discussed.