Kiwifruit size and CPPU response are influenced by the time of anthesis

The cytokinin-active compound, N-1-(2-chloro-4-pyridyl)-N-3-phenylurea (CPPU), applied at different flowering dates, affected final 'Hayward' kiwifruit size. Ovaries from early opening flowers had significantly greater (P less than or equal to 0.05) length, diameter, and fresh and dry weight than late ovaries. Cell number and cell size in the inner and outer pericarp of the ovary at anthesis were similar for early and late opening flowers but core cell number was significantly higher (P < 0.05) in the early flowers. Fruit shape and ovary dry matter percentage at harvest was unaffected by the time of anthesis. When fruitlets from both types of flowers were treated with CPPU at 15 mul l(-1) there was a significant interaction, with the early flowers achieving a much larger commercial fruit size (153 g) than fruit from later flowers (126 g). CPPU-treated fruit from the two bloom dates achieved higher cell number in the outer pericarp at harvest. In contrast, the cell size in the inner pericarp of early and late untreated fruits was higher than CPPU-treated fruit. Pre-anthesis factors and early fruit growth were important in determining final fruit size. (C) 2002 Elsevier Science B.V. All rights reserved.