Sex-Linked Molecular Markers Identify Female Lines in Endosperm-Derived Kiwifruit Callus and in Regenerants

This is the first report of molecular markers application for the analysis of endosperm-derived callus and nonaploid kiwifruit (Actinidia chinensis var. deliciosa, formerly: Actinidia deliciosa) plants. As a source of explants, fruits of 'Hayward', the most popular cultivar, were used. Additionally, analyses of the nuclear DNA content and sex were conducted on the regenerated plants. Hexaploid seedlings were used as control for the flow cytometric analyses. Most of the plants (about 90%) regenerated via endosperm-derived callus possessed 2C = 9Cx DNA, which confirmed their endosperm origin and nonaploidy. Because Actinidia is a dioecious species, and female plants bearing fruits are desired by breeders, it is crucial to identify the sex of an individual at early stages of development. Analyses were conducted with ex vitro and in vitro samples. Results revealed that specific markers for a Y-chromosome applied at the callus stage allowed us to reliably predict the sex of plants regenerated from it. This is a novel application of sex-linked markers for early selection of female and male callus lines when the sex of the initial explants is still unknown, such as fresh isolated embryos and endosperm. It may have significant importance for breeding kiwifruit programs, which involve tissue culture techniques.