Among 38 lines of tetraploid triticale analyzed at meiosis, the number of paired arms per rye chromosome ranged from 1.14 to 1.76 and from 1.46 to 1.96 per wheat chromosome. The frequency of cells without univalents ranged from 22 to 90%. Pairing frequencies within rye and wheat genomes were correlated in all groups of lines. Lines without wheat chromosome 3B showed reduced pairing in both genomes, while lines with an additional pair of 5R chromosomes substituted for group-5 wheat chromosomes showed improved pairing of the rye genome but not of the wheat genome. In the rye genome, the chromosome arms that carry major blocks of telomeric heterochromatin paired with an average of 25.1% lower frequency than the arms without the telomeric heterochromatin, the difference being attributed to the difference in arm length and not to the presence of heterochromatic blocks. In the wheat genome, chromosome arms IBS, 5AS, and 5BS and chromosomes 4A and 7B paired with significantly lower frequency than the remaining arms of wheat chromosomes. Average aneuploid frequency in a sample of 1383 plants was 4.55%, with the mean value of 5.77% in lines with 14 wheat and 14 rye chromosomes, and 2.01% in lines with an extra pair of 5R chromosomes. The results indicate that while the meiotic pairing is poorer and aneuploid frequency is higher than previously believed, tetraploid triticales are nevertheless chromosomally much more stable than hexaploid or octoploid triticales. Key words: C-banding, heterochromatin, paired arms, chromosome substitution.
PAIRING COMPETITION BETWEEN IDENTICAL AND HOMOLOGOUS CHROMOSOMES IN RYE AND GRASSHOPPERS