The aim of this research was to improve the efficiency of previous techniques for the production of haploid onion plants through in vitro gynogenesis. Taking into account the last published results, two experiments were carried out: (1) unpollinated ovule culture of the long-day cv 'Erso 1'; (2) ovary and whole flower culture of the long-day cvs 'Cosmic', 'Morgana' and of the short day cvs 'KLR', 'Senshyu Yellow'. The yield of gynogenic embryos from ovule culture significantly increased when: (1) 100 g/l of sucrose was supplied in both preculture and culture media and (2) 2,4-dichlorophenoxyacetic acid (2,4D) and 6-benzyladenine (6BA) were both used at 2 mg/l in the preculture medium. Embryo yield from ovary culture was significantly improved in the four cvs by using a modified BDS medium containing 100 g/l of sucrose, 1 mg/l of naphthaleneacetic acid (NAA) and 2 mg/l of 6BA; a high percentage of embryos were induced from direct flower culture by using a modified BDS medium containing 100 g/l of sucrose, 2 mg/l of 2,4D and 2 mg/l of 6BA. Statistical analysis of the data revealed a close relationship between the kind of cultured organ (ovary or flower) and the type of auxin in the medium. Ovary culture gave the best yield in the presence of NAA while 2,4D gave good results in both ovary and flower culture. Thirtysix per cent of the embryos obtained could regenerate whole plantlets and 88.3% of the regenerants were haploid. The capacity of each type of organ to produce embryos was also influenced by the genotype used and, perhaps, by the environmental conditions of donor plant growth. For this reason, gynogenesis induction should always make use of both ovary and flower culture.
