Interspecific hybridizations with an African tobacco, Nicotiana africana Merxm

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Abstract
A recently discovered species from Africa, N. africana Merxm., was crossed as the male to 27 other species of the genus. Germinable seeds were obtained from nearly all crosses, but most seedlings died. Crosses with N.fragrans from the South Pacific, however, produced vigorous hybrids. Cytological and biochemical evidence sug gest some taxonomic affinity between N. african and N. fragrans, but it remains puzzling how N. africana, or its ancestor(s), reached Africa. Crosses of normal and 23 monosomic types of N. labacum with N. africana produced very rare hybrids with various chromosome numbers and also some maternal haploids. In contrast, mono somic-H, when pollinated by N. africana hybridized readily; the hybrids analyzed lacked one chromosome, presumably the H. Thus, absence of an H chromosome greatly facilitates the survival of hybrids, though it is not clear from the evidence whether possession of an intact H completely prevents hybrid survival. Chromosome pairing in N. tabacum x N. africana hybrids was of the “low variable” type.