Development of Flat and Fan-Shaped Fruit in Actinidia chinensis var. chinensis and Actinidia deliciosa

Abstract

We describe and quantify development of flat and fan-shaped fruit of Actinidia chinensis var. chinensis from inception to maturity. Flat fruit arise from particularly large and flat floral meristems. After bract initiation, the terminal flower remains elliptic in cross section, produces elliptic whorls of floral organs, and forms a flat-shaped ovary. The allometry of the ovary does not change from inception to maturity. Fan-shaped fruit develop from exceptionally flat floral meristems. They result from postgenital fusion of the terminal flower with one or two precocious lateral flowers. Timing of the fusion process varies, resulting in a variable degree of integration of tissues. The fasciated flower has supernumerary floral organs, and is borne on a single pedicel. The histology of mature flat and fan-shaped fruit is described for commercially-grown Actinidia deliciosa cv. Hayward. Mature flat fruit have a larger maximum diameter, but are comparable to normal fruit in the minimum diameter. Flat fruit have more locules and more pericarp tissue than normal fruit, but these are not causally related to fruit shape. The flat shape can be attributed to differential planes of enlargement of cells in certain regions of the central core. Mature fan-shaped fruit are larger, and have more pericarp, core and locules than normal or flat fruit.