Endosperm-derived triploid plant regeneration in diploid Actinidia kolomikta, a cold-hardy kiwifruit relative

Abstract

Endosperm culture is a unique technique for producing a triploid plant from diploid plants. In the present study, endosperm of a diploid cold-hardy kiwifruit relative, Actinidia kolomikta (Maxim. & Rupr.) Maxim., was cultured to regenerate triploid plants and expand ploidy variation in this mostly diploid species. Endosperm derived from fruits harvested 6–10 weeks after flowering (WAF) was used for the initial explants to examine the effect of plant growth regulators on callus formation and organogenesis. The endosperm-derived calli induced in MS medium with above 1.0mgL−1 of 2,4-dichlorophenoxyacetic acid (2,4-D) were soft, small, and translucent, and no morphogenic response was observed. Conversely, the endosperm-derived yellow-green calli induced in the medium with 2,4-D (0.1mgL−1) plus kinetin (1.0, 2.0, and 5.0mgL−1) were hard, compact, fast growing, and showed adventitious shoot primordia. These primordia elongated into shoots when the calli were transferred to MS medium supplemented with zeatin (1.0, 2.0, and 4.0mgL−1) under continuous light conditions. The shoots developed roots on half-strength MS medium lacking plant growth regulators. In total, 14 plants were obtained. Flow cytometry and chromosomal analysis confirmed that the regenerated plants were triploid, suggesting that the plant tissue originated from the endosperm. This study reveals that the endosperm of A. kolomikta has plant regeneration abilities and that the regenerated plants have the same ploidy level as the endosperm (triploid). These results may be of use for ploidy manipulation or polyploidy breeding in other species in the genus Actinidia.