CYTOGENETIC STUDIES OF NICOTIANA

Abstract

The three species, N. alata (n=9), N. longiflora (n=10) and N. plumbaginifolia (n=10), were crossed each with N. glauca (n= 12). The crosses N. glauca×N. alata and N. glauca ×N. plumbaginifolia gave some seeds, while no seed was obtained from the cross N. glauca ×N. longiflora. Of the reciprocal crosses, N. alata×N. glauca gave no seed, but N. longiflora ×N. glauca produced some germinating seeds.The external characters of the hydrids which were produced from the seeds of N. glauca× N. alata and N. glauca×N. plumbaginifolia agreed with Kosteff's description of those of the same hydrids. No report of the hybrid N. longiflora×N. glauca has been published, so far as I know. The features of this hybrid were in agreement with Kostoff's descriptson of those of the hybrid of the reciprocal cross.All the hybrids mentioned above showed considerable irregularities in meiotic behaviour in PMC's. Polysporous PMC's were. often observed and the hybrids were completely sterile.At first metaphase in the hybrid N. glauca×N. plumbaginifolia, 0-4 bivalents were counted with the mode at 2II.In the hybrid N. glauca×N. alata, 0-7 bivalents were observed, and the most frequent configurations found were 3II+15I and 4II+13I.In the hybrid N. longiflora×N glauca, the number of bivalents was 1-6 and the typical configuration of the chromosome complement was 6II+10I, though the frequency of this combination was low in proportion among the observed PMC's, since polyvalents ranging from tri- to octa-valents were often found. The chromosomes of this plant showed sticky trend at meiosis, and the divisions were more irregular than those in the above two hybrids. Such remarkable irregularities were not found in the reciprocal cross made by Kostoff, or in the hybrid N. glauca×N. plumbaginifolia according to Kostoff and Goodspeed, in which the paternal parent was taxonomically closely related to N. longiflora.These irregularities may be due to the difference in the degree of affinity between the maternal plant, N. longiflora, and the chromosomes of the paternal plant, N. glauca, which was probably lower in this direction of the cross than in the reciprocal direction.The above findings about the three hybrids suggest the presence of a few partially homologous chromosomes between. N. glauca on one side and N. alata, N. plumbaginifolia or N. longiflora on the other. More over, a few chromosomes in diplotene and diakinesis showed end to end junctions, and anaphasic chromosome bridges were always observed.