Source-sink relations in kiwifruit : carbohydrate and hormone effects on fruit growth at the cell, organ and whole plant level : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Physiology and Horticultural Science at Massey University, Palmerston North, New Zealand

Abstract

Fruit weight of Actinidia deliciosa, A. chinensis. and A. arguta kiwifruit was correlated with fruit cell number and seed numbers or seed weight within and between species. Reducing seed number of A. deliciosa 'Hay ward' by style excision reduced fruit weight and cell size, but had only minor effects on cell number. It is suggested that the impact of genotype on fruit weight was by determining the number and size of ovules available to be fertilised and form seeds. At a leaf:fruit ratio of four, girdling of lateral shoots increased fruit weight mainly due to increased cell expansion. Fruit cell numbers were also increased when girdles were applied during post-anihesis cell division. Girdling of individual canes with a high leaf:fruit ratio also increased mean fruit weight. However when more canes were girdled on a vine, the response to girdling was decreased, and fruit weight in non-girdled canes was lower. These negative effects on fruit growth were not due to reduced root function or increased competition for photo-assimilate. Increased cane girdling resulted in a transitory increase in the concentration of cytokinins extracted from girdled canes, and this was correlated with increased bud-burst. The increased vegetative growth may have inhibited fruit growth on girdled canes, but no explanation was found for the reduced fruit weight in non-girdled canes. An inhibitory effect of high seeded kiwifruit on the growth of low seeded kiwifruit was confirmed, and could be accounted for by increased seed abortion from inhibited fruit. Diffusible IAA from kiwifruit increased over time, but was not associated with inter-fruit competition or fruit seed number. Application of the auxin transport inhibitor N-l-naphlhylphthalamic acid (NPA) to kiwifruit pedicels after fruit set, reduced fruit fresh weight and dry matter accumulation. However late NPA application had no effect on fruit weight, which suggests that IAA transport is not essential for kiwifruit growth at all times. Application of N-(2-chloro-4-pyridyl-N'-phenylurea (CPPU) to A. deliciosa and A. chinensis kiwifruit selections increased fruit weight, but application of adenine based cytokinins in combination with CPPU increased fruit weight further. CPPU application resulted in a transitory decrease in fruit abscisic acid levels.