Effect of CPPU (cytokinin) treatments on fruit anatomical structure and quality in Actinidia deliciosa

In 1994 a study was carried out to evaluate the influence of CPPU treatments on fruit anatomical structure and quality in Actinidia deliciosa cv. Hayward. Fifteen days after full bloom about 450 fruits of similar size were labeled on four vines; one-third were then completely dipped in CPPU solution (20 ppm), one-third were half dipped in CPPU solution and one-third were completely dipped in water (control). CPPU treatment induced a significant increase in fruit size (+55%). No differences in size were observed between fruits completely or partially dipped in CPPU solution. An increased growth of all the different fruit tissues (outer pericarp, inner pericarp and core) was promoted by CPPU, without modifying their relative proportions. Two different kinds of cells were distinguished in the pericarp and in the core tissues: very large cells (LC) and small cells (SC). CPPU stimulated both cell division and elongation: the increased size in the different fruit tissues was due to increases in the number and size of the SC in the outer and inner pericarp and to higher cell number in the core. CPPU deformed the fruit shape by causing a protrusion of the distal end of the fruits. At harvest, treated fruits had a higher soluble solid content and a lower total titratable acid content and less flesh firmness than the control, suggesting an earlier ripening.