Isogenous lines were obtained by doubling the chromosomal set of androgenetic haploids achieved byïn vitro"anther culture derived from inter- and intraspecific Nicotiana hybrids that were in the F1-F4 generation. Dihaploid genomes that include genetic information from Nicotiana glutinosa and Nicotiana glauca are used as initial material for quality improvement to obtain virus-resistant tobacco forms. Tabacum-type dihaploid genomes having some useful characteristics were checked in the last steps of the improvement process for their acceptance as new varieties. Virginia 501 and 496 and the semi-oriental 504-type line are remarkable for their productivity and quality index. Cytogenetic analysis of dihaploid genomes reveals the stability of chromosome number and morphology, as well as a quite normal meiotic division.