Embryo rescue by half-ovule culture for the production of interspecific hybrids in Alstroemeria

Abstract

Interspecific hybridization in the genus Alstroemeria is hindered by post-fertilization barriers. Histological analysis revealed poor endosperm development from 18 days after pollination onwards, followed by malformation and abortion of embryos. To create interspecific hybrids between Alstroemeria aurea, Alstroemeria pelegrina, Alstroemeria magnifica, Alstroemeria inodora and Alstroemeria psittacina in diallelic combinations, an ovule culture technique was developed. Influence of age of ovules, sucrose concentration of medium and temperature and light during culture were tested. Harvesting ovules before the onset of endosperm degeneration, i.e. at 14 days after pollination, cutting them into halves and culturing the micropylar halves in a rotating liquid culture medium containing 6% sucrose at 21 °C in the dark, led to successful embryo rescue. Germinated embryos were subcultured in vitro until rhizomes were formed, a prerequisite for successful transfer to the greenhouse. Full grown plants all showed interspecific morphological traits and analysis of chromosome complement confirmed their hybrid nature. Diploid hybrid plants were obtained in all the 20 interspecific 2 x-2 x combinations. A total of 260 interspecific hybrid plants was produced. Half-ovule culture of 2 x-4 x and 4 x-2 x crosses resulted in 43 triploid hybrid plants. Because interspecific hybrids were obtained in 100% of the interspecific combinations, it is expected that the described technique can be applied to overcome post-fertilization barriers in most crosses within the genus Aktroemeria.