Hormonal regulation of fruit set, parthenogenesis induction and fruit expansion in Japanese pear

The effects of applied gibberellins (GAs), GA(1), GA(3), GA(4) and GA(7) with a cytokinin, N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) and indole-3-acetic acid (IAA) on fruit set, parthenogenesis induction and fruit expansion of a number of Rosaceae species were assessed. These included Japanese pear cv. 'Akibae' (self-compatible) and cv. 'Iwate yamanashi' (a seedless cultivar). Other Rosaceae species (Pyrus communis, Chaenomeles sinensis, Cydonia oblonga, and Malus pumila) were also investigated. GA(4), GA(7) and CPPU are very effective in inducing parthenocarpic fruit growth, whereas GA(1), GA(3) and IAA, have no ability to induce parthenogenesis in Japanese pear. GA(4)- and GA(7)-induced parthenocarpic fruit tended to be smaller in size, higher in flesh hardness, and showed advanced fruit ripening in comparison to pollinated fruit and to parthenocarpic fruit induced by CPPU. GA(4)- and GA(7)-induced parthenocarpic fruit also had an increased pedicel length and fruit shape index and also showed a slight protrusion of the calyx end. CPPU, GA(4) and GA(7) alone or combination with uniconazole were also active in inducing parthenogenesis in three other Rosaceae species, although final fruit set was extremely low. GA(1) was essentially inactive in promoting fruit expansion unlike the other bioactive GAs, whose effectiveness in promoting fruit cell expansion was as follow: GA(4) approximate to GA(7) > GA(3) > GA(1).