[Show abstract][Hide abstract] ABSTRACT: The subgenus Ceratochloa of the genus Bromus includes a number of closely related allopolyploid forms or species that present a difficult taxonomic problem. The present work combines data concerning chromosome length, heterochromatin distribution and nuclear genome size of different 6x, 8x and 12x accessions in this subgenus. Special attention is paid to the karyotype structure and genomic constitution of duodecaploid plants recently found in South America. Hexaploid lineages possess six almost indistinguishable genomes and a nuclear DNA content between 12.72 pg and 15.10 pg (mean 1Cx value = 2.32 pg), whereas octoploid lineages contain the same six genomes (AABBCC) plus two that are characterized by longer chromosomes and a greater DNA content (1Cx = 4.47 pg). Two duodecaploid accessions found in South America resemble each other and apparently differ from the North American duodecaploid B. arizonicus as regards chromosome size and nuclear DNA content (40.00 and 40.50 pg vs. 27.59 pg). These observations suggest that the South American duodecaploids represent a separate evolutionary lineage of the B. subgenus Ceratochloa, unrecognized heretofore.
[Show abstract][Hide abstract] ABSTRACT: B. 2007. Karyotype analysis of hybrids of reciprocal crossings between [4x] Phleum commutatum Gaud. and [4x] Phleum pratense L. Acta Agr. Silv. Ser. Agr. 48: 15–31. The paper presents the results of the research on the karyotype structure and amount of nuclear DNA in reciprocal hybrids between the tetraploid alpine cats tail grass and the tetraploid timothy grass. The hybrid forms were grown from F1 grains. For the karyotype analysis staining in acetic orceine and C-banding were used. Nuclear DNA measurements were taken in a flow cytometer. In the root apical meristem of the two forms the authors revealed the occurrence of an unstable chromosome number — apart from the typical tetraploid number 2n = 28, different aneuploid numbers were recorded. The band karyotype shows the occurrence of the same telomeric type of heterochromatin distribution, characteristic of the genomes of one of the parental forms — P. pratense [4x], no matter if it was a maternal or paternal form in the crossing.