| A.trachycaulum was given the formula S1S1B1B1
in this study. One of the basic genomes of tetraploid A. semicostatum
showed high pairing with one of the genomes of A. trachycaulum (6.56II)
which indicates close homology. SCHULZ-SCHAEFFER et al. (1963) found
2 pairs of an F-type satellite indicator chromosome in hexaploid
A. semicostatum which suggested the presence of 4 spicatum genomes
in this species. Consequently, hexaploid A. semicostatum should be
an autoalloploid with the genome formula S1S1S1S1YY.
If two genomes of the hexaploid are of the S1 type, it is very
likely that at least one genome of tetraploid A. semicostatum is
an S1 genome. Chromosomes of the second genome of tetraploid
A. semicostatum did not pair with chromosomes of A. trachycaulum.
The origin of this genome (Y) is unknown. For these reasons we gave tetraploid
A. semicostatum the genome formula S1S1YY (Table
3). A group of 3 species showed very close relationship. These were A. subsecundum (S2S2B2B2), A. latiglume (S2S2B2B2) and A. caninum (S2S2B2B2). Average bivalent pairing between these 3 species was 12.15 and 12.10, respectively. One of these 3 species, A. caninum, was crossed with A. riparium and A. arizonicum. Lower bivalent pairing was observed in both crosses averaging 11.62 and 10.13, respectively. Consequently, the genome formulas assigned were S3S3B3B3 (A. riparium) and S4S4B4B4 (A. arizonicum). Relatively low bivalent pairing (10.28) was found between the two basic genomes of A. riparium and two of the 3 genomes of A. brachyphyllum. The third genome ( X ) of A. brachyphyllum formed univalents (7.13I) and could not be identified. The genome formula given for A. brachyphyllum was S5S5B5B5XX (Table 2 and 3.) SCHULZ-SCHAEFFER and JURASITS (1962) and SCHULZ-SCHAEFFER et al. (1963) in a study of genome indicator chromosome, theorized that all 8 species analyzed here carry the spicatum genome (indicater chromosome type F-1, F-2). This earlier hypothesis is substantiated by the data presented and by work of other authors. |
| <-- Back |