INTERACTIONS BETWEEN CYTOKININ-ACTIVE SUBSTANCES AND FRUIT GROWTH OF ACTINIDIA DELICIOSA (GREEN KIWIFRUIT) AND AN ACTINIDIA CHINENSIS SELECTION

The limiting hormone for fruit growth in Actinidia deliciosa appeared to be cytokinins. N-(2-cloro-4-pyridyl)-N’-phenylurea (CPPU) dramatically stimulated growth of both A. deliciosa and some A. chinensis selections, but natural cytokinins and other synthetic cytokinins had only low activity. Evidence is presented that CPPU interacts positively with naturally occurring cytokinins in stimulating fruit growth of kiwifruit, suggesting a possible protective role for CPPU. However an effective natural stimulant of an A. chinensis selection (gold fleshed) does not appear to have cytokinin activity even though the fruit responds to CPPU and, in general CPPU did not seem to increase endogenous cytokinins of A. deliciosa as determined by radioimmunoassays. These results are discussed in terms of the interaction and mechanism of action of plant growth regulators in controlling fruit growth.