Abstract
1) At MI in PMC's of F1 N. sylvestris (n=12)×N. otophora (n=12), a pairing range 0-5 was found with mode at 2-3. In the same hybrid Goodspeed (1954) observed 0-7 bivalents with mode at 3.
2) At MI in PMC's of F1 N. sylvestris (n=12)×N. tomentosa (n=12), 0-7 bivalents were found with mode at 3. Goodspeed (1954) found pairing ranges of 0-7 with mode at 3 and 0-7 with mode at 2-3 respectively in F1 N. sylvestris×N. setchellii and F1 N. sylvestris× N. tomentosa. Kostoff (1943) found, in F1 N. sylvestris×N. tomentosa, usually univalents or 1 to 4 bivalents and rarely more than 4 bivalents. He also observed, in F1 N. sylvestris×N. tomentosiformis, somewhat less bivalents than in the former. The writer (1955) found 1-9 bivalents with mode at 4 in F1 N. sylvestris×N. tomentosiformis. From the results mentioned above, we can assume 2-4 homologous chromosomes or large homologous portions between sylvestris genome and the genomes of the tomentosa group.
3) At MI in PMC's of F1 N. tabacum (n=24)×N. solanifolia (n=12), a pairing range 1-5 was found with mode at 1. Goodspeed also found 0-7 bivalents with mode at 2. Accordingly the conjugational affinity between tabacum and solanifolia genomes is assumed to be generally the same as the intragenomatic affinity in N. tabacum.
4) At MI of PMC's of F1 N. Debneyi (n=24)×N. tabacum (n=24), 0-6 bivalents were found with mode at 2. Kostoff also found usually univalents or 1-3 bivalents. From these results it appears that there may be no pairing between tabacum and Debneyi genomes, since a few intragenomatic affinities in N. tabacum are present.
5) At MI of PMC's of the hybrid N. rustica×N. paniculata, the writer observed a univalent range 2-12, a bivalent range 2-12 and a trivalent range 0-10. In the same hybrid, Goodspeed found usually 12 bivalents and occasionaly 1 trivalent or rarely 2 trivalents. Kostoff also found usually 12 bivalents and 12 univalents, and rarely 1 trivalent. The writer observed more trivalents, but N. paniculata is recognized to be one of the ancestors of N. rustica.
