Structure and development of kiwifruit skins

The genusActinidiacontains species with a wide variety of fruit appearances and skin types. The structure of the skin and associated tissues from three commercial species—Actinidia arguta(‘Hortgem Tahi’),Actinidia chinensis(‘Hort16A’), andActinidia deliciosavar.deliciosa(‘Hayward’)—has been examined.Actinidia argutahas the simplest skin structure consisting of an epidermis, with a thick cuticle, and a hypodermis that is one to two cells thick. The skin is essentially hairless. In contrast, the skins of bothA. chinensisandA. deliciosahave a more complex structure comprising a thick layer of dead, radially compressed cells with suberized cell walls over the hypodermis. In both species, simple uniseriate and complex multiseriate hairs are present. InA. deliciosa, parenchyma cells beneath the hypodermis gradually merge into the fleshy tissue that forms most of the outer pericarp. However, inA. chinensis, this region is separated from the outer skin by a zone containing a mixture of parenchyma and brachysclereides (stone cells). Skin development inA. argutacomprises cell division and cell expansion accompanied by increased cell wall thickness and the development of a thick cuticle. The development of the skin ofA. deliciosaandA. chinensisis a more complex, ordered process of cell death, cell wall suberization, and collapse of individual layers beginning with the epidermal layer ca. 7 wk after petal drop. InA. chinensis, an unusual feature is the development of a very thin‐walled, poorly staining, fragile layer just under the developing skin midway through fruit development.