Preferential Recovery of Somatic Hybrids from Protoplast Fusion of two Nicotiana Species in the Absence of Artificial Selection

Mesophyll protoplasts of Nicouana plwnbaginifoJia (PP) and N. sylvestris (SS) were mixed at equal density, treated with polyethylene glycol (PEG) and then cultured in medium with no selection pressure against parental cells. Cytological, morphological, and biochemical studies showed that about 78%of plants regenerated from protoplast fusion were somatic hybrids. The ploidy levels of somatic hybrids varied, and the frequencies of plants with PPSS, PPPPSS, and PPPPSSSS genome constitutions were 84.8%, 8.7%, and 6.5%, respectively. Aneuploid numbers and chromosome structural changes were common in somatic hybrids. The- successful recovery of somatic hybrids in the absence of artificial selection is attributed to a high viability of the fusion products following PEG treatment and a fast rate of growth and development of hybrid cells during in vitro culture.