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Although several methods have been developed for producing haploid plants, the in vitro techniques are much more efficient than inter-specific hybridization or treatment with plant-growth regulators, temperature or irradiation. Androgenesis is the most universal of these techniques but ovule culture and the bulbosum method could complement or replace anther culture in those species or genotypes with less responsive male gametes. Genotype, environment, physiological status of the donor plant, and culture conditions and components all need to be taken into account when developing procedures for producing haploid and dihaploid plants. Suitable methods are already well established for a number of important crops. However, many problems, related to regeneration frequency, gametoclonal variation and albinism, are still unsolved. It is now clear that haploids and dihaploids form the ideal system for genetic manipulation in plants. Their key role in producing new theoretical and applied knowledge in plant science is an important aspect of our review.

The present work deals with the in vitro methods for rapid propagation, and morphogenetic potential of the rare and endangered bulb species Leucojum aestivum L., Amaryllidaceae, and Lilium rhodopaeum Delip., Liliaceae. The morphogenetic potential of different plant organs (bulb, stem, leaves and ovaries) was studied. Leaves of Leucojum aestivum L. and basal parts of the bulb in Lilium rhodopaeum Delip. possess the highest regeneration activity. Murashige and Skoog (MS) medium + 1 mg/l 6-benzylaminopurine (BAP) + 1 mg/l kinetin and Linsmaier and Skoog (LS) medium + 0.5 mg/l 1-naphthaleneacetic acid (NAA) + 0.1 mg/l kinetin were favourable for direct organogenisis from these explants. A stimulating effect of alow gamma-irradiation dose (5 Gy) upon the quantity and growth intensity of the bulbs formed by the explants in in vitro conditions is observed.

The incompatibility between the wild species N. africana Merxm. and the cultivated species N. tabacum has been overcome by in vitro techniques. Underdeveloped Fo seeds, placed on MS medium with supplements, produced plants which upon reaching the stage of anthesis proved to be completely sterile. Female sterility of F~ hybrids was overcome by applying tissue culture methods. Explants of stem parenchyma were grown in vitro. In every passage investigations were made of their callus production, organogenesis and cell polyploidization. The regenerants showed a great diversity in their morphological and cytological characters. Pollination of the R~ plants (N. africana x N. tabacum) with N. tabacum produced normally seeded capsules. BC~ plants were male sterile. The male sterility of the first backcross generation was preserved in BC2 and BC3, proving its cytoplasmic origin.