Boldrini K R, Adamowski E V, Silva N, Pagliarini M S, Valle C B
Departamento de Biologia Celular e Genética, Universidade Estadual de Maringá, Maringá, PR, Brasil.
Genet Mol Res. 2011 Feb 1;10(1):169-76. doi: 10.4238/vol10-1gmr990.
Brachiaria humidicola is a grass adapted to seasonally swampy grasslands in Africa; two cultivars, 'common' and Llanero, are widely used in Brazilian pastures. New cultivars are in great demand in order to diversify current production systems to achieve improved quality and yield. Cytological analyses of 55 accessions of this species available from the Embrapa Beef Cattle germplasm collection revealed that 27 are apomictic and have 2n = 54 chromosomes. Chromosome pairing as bi- to nonavalent associations at diakinesis indicated a basic chromosome number in this species of x = 6, as found in other closely related Brachiaria species. Thus, these 27 accessions are nonaploid (2n = 9x = 54). Abnormalities were found in the meiosis of these accessions, at variable frequencies. The most common abnormalities were those related to irregular chromosome segregation, which led to unbalanced gamete formation; but chromosome stickiness, cell fusion, and absence of cytokinesis were also recorded. Although some accessions have a low frequency of meiotic abnormalities, ensuring potentially good pollen viability, these cannot be used in hybridization due to a lack of sexual accessions with the same ploidy level.
湿生臂形草是一种适应非洲季节性沼泽草原的草；两个品种，即“普通”品种和利亚内罗品种，在巴西牧场广泛使用。为了使当前生产系统多样化以提高质量和产量，对新品种的需求很大。对巴西农牧业研究公司肉牛种质资源库中现有的55份该物种材料进行的细胞学分析表明，其中27份是无融合生殖的，且有2n = 54条染色体。在终变期，染色体配对为二价体至九价体联合，这表明该物种的基本染色体数为x = 6，这与其他亲缘关系密切的臂形草物种的情况一致。因此，这27份材料是九倍体（2n = 9x = 54）。在这些材料的减数分裂中发现了不同频率的异常情况。最常见的异常情况是与染色体不规则分离相关的异常，这导致了不平衡配子的形成；但也记录到了染色体粘连、细胞融合和胞质分裂缺失的情况。尽管一些材料减数分裂异常的频率较低，保证了潜在的良好花粉活力，但由于缺乏相同倍性水平的有性材料，这些材料不能用于杂交。
