The three species,
N. trigonophylla, N. undulata and
N. rustica were crossed reciprocally with
N. tabacum. The crosses
N. tabacum×N. trigonophylla, N. undulata×
N. tabacum and
N. tabacum (Odaruma) ×
N. rustica (Afghanistan) gave some seeds, while no seeds were obtained from the three remaining crosses. No report on the hybrids
N. tabacum×N. trigonophylla and
N. undulata×N. tabacum or their reciprocal crosses has been published, so far as I know.
In external characters the F
1 tabacum-trigonophylla, is somewhat smaller than
N. tabacum, the leaf form is intermediate between those in the parents, and the flower colour is a pale red. F
1 undulata-tabacum is more similar to
N. tabacum than to
N. undulata, but its flowers are pale yellowish red, showing an intermediate color between the two parents. The morphology of F
1 tabacum-rustica agrees with that of Kostoff's description of the reciprocal hybrid (
N. rustica ×N. tabacum). These three hybrids were all vigorous.
All the hybrids mentioned above, showed considerable irregularities in the meiotic behaviour of the FMC's. Polysporous PMC's were often observed, and the hybrids were completely sterile.
At first metaphase in F
1 tabacum-trigonophylla, 0-11 bivalents, mostly 5-6, were counted. In F
1 trigonophylla-tomentosa and F
1 trigonophylla-tomentosiformis, Kostoff (1941-43) observed 2-10 and 0-8 bivalents, respectively. Accordingly, the chromosome conjugation in F
1 tabacum-trigonophylla is assumed to be caused mostly by semihomologous chromosomes between the
trigonophylla genome and the
tomentosa subgenome, not the
sylvestris subgenome, of
N. tabacum. In F
1 undulata-tabacum, 0-8 bivalents, mostly 3-5, were observed. In this hybrid the number of the bivalents is a little more than that of the chromosome conjugation in haploid
tabacum or F
1 sylvestris-tomentosiformis. Accordingly it is assumed that a few semihomologous chromosomes are present between the
undulata genome and the two subgenomes of
N. tabacum. In F
1 tabacum-rustica, 1-10 bivalents (also multivalents) were formed at the first metaphase and some secondary associations were observed at first and second metaphases. Christoff (1928) and Trenovsky (1935) also observed a small number of bivalents in F
1 rustica-tabacum, while Kostoff (1941-43) found many bivalents, as many as 5-24, in the same hybrid. The cause of there different results was not determined.
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