In the last few decades human pressure on natural ecosystems has greatly risen, The abundance and diversity of many valuable species of plants and animals have accordingly been markedly reduced (Voinstvenskyi, 1986; Sytnik, 1988; Chopyk, 1983). Modern achievements of genetic and cell engineering could be used to conserve plant gene banks in Ukraine. The technique of constructing cytoplasmic hybrids by distant somatic hybridization is very useful in this respect. This method has been successfully developed at the laboratories of the Institute of Cell Biology and Genetic Engineering in Kiev, under the leadership of Academician Yu.Yu. Gleba. For construction of cybrids (cytoplasmic hybrids) the following wild plants from the Solanaceae were used: Nicotiana tabacum L. (donor of protoplasm), Atropa belladonna L., Scopolia carniolica Jacq. and Hyoscyamus niger L. (donors of cytoplasm). Between 1995 and 1997, a special study was made of ontogenesis and phenorhythmics of cybrids, and an assessment of their allelopathic influence on other plants was carried out. The experiment showed that the energy of cybrid seed germination is lower than that of parent plants. Tobacco and belladonna seeds germinated 5-7 days after sowing, whereas cybrid seed germinated in 9-11 days, and the term of germination was longer, at 13-19 days. During ontogenesis cybrid fertility occurred earlier (in 70-90 days) than in natural plants (tobacco was 85-110 days). The morphology of resulting plants also differed from that of the parents. They were smaller, with modified leaves, double flowers, sometimes with no corolla in the perianth and with complete male sterility. Experiments dealing with the allelopathic activity of initial wild plants (tobacco, belladonna, Scopolia) and cybrids of the Solanaceae obtained using the method of Ivanov & Bystrova (1986), were performed, using shoots of cucumber cultivar "Konkurent" for the test. The shoots were found to be much more allelopathically affected by the Nicotiana tabacum + Hyoscyamus niger cybrid than by Nicotiana tabacum. The Nicotiana tabacum + Scopolia carniolica cybrid showed nearly the same allelopathic activity as Nicotiana tabacum. Cybrids of the Solanaceae obtained are thus economically very useful for selection of cultivated plants and for conservation of natural plant genes in Ukraine and other countries.