Pagliarini M S, Valle C B, Santos E M, Mendes D V, Bernardo Z H, Mendes-Bonato A B, Silva N, Calisto V
Departamento de Biologia Celular e Genética, Universidade Estadual de Maringá, Maringá, PR, Brasil.
Genet Mol Res. 2012 May 15;11(2):1309-18. doi: 10.4238/2012.May.15.1.
The genus Brachiaria comprises more than 100 species and is the single most important genus of forage grass in the tropics. Brachiaria brizantha, widely used in Brazilian pastures for beef and dairy production, is native to tropical Africa. As a subsidy to the breeding program underway in Brazil, cytological studies were employed to determine the chromosome number and to evaluate microsporogenesis in 46 accessions of this species available at Embrapa Beef Cattle (Brazil). Thirty-four accessions presented 2n = 36; seven had 2n = 45, and five had 2n = 54 chromosomes. Based on the higher level of chromosome association observed in diakinesis, in tetra-, penta-, and hexavalents, respectively, it was concluded that they are derived from x = 9; consequently, these accessions are tetra- (2n = 4x = 36), penta- (2n = 5x = 45), and hexaploids (2n = 6x = 54). The most common meiotic abnormalities were irregular chromosome segregation due to polyploidy. Chromosome stickiness, abnormal cytokinesis, non-congressed bivalents in metaphase I and chromosomes in metaphase II, and chromosome elimination were recorded at varying frequencies in several accessions. The mean percentage of meiotic abnormalities ranged from 0.36 to 95.76%. All the abnormalities had the potential to affect pollen viability by generating unbalanced gametes. Among the accessions, only the tetraploid ones with less than 40% of abnormalities are suitable as pollen donors in intra- and interspecific crosses. Currently, accessions with a high level of ploidy (5 and 6n) cannot be used as male genitors in crosses because of the lack of sexual female genitors with the same levels of ploidy.
臂形草属包含100多个物种，是热带地区最重要的饲草属。臂形草广泛用于巴西牧场的肉牛和奶牛生产，原产于热带非洲。作为对巴西正在进行的育种计划的补充，进行了细胞学研究，以确定巴西农牧业研究公司肉牛部（巴西）现有的46份该物种材料的染色体数目并评估其小孢子发生。34份材料的染色体数目为2n = 36；7份为2n = 45，5份为2n = 54。根据在终变期观察到的较高水平的染色体联会，分别在四价体、五价体和六价体中，得出它们源自x = 9；因此，这些材料分别为四倍体（2n = 4x = 36）、五倍体（2n = 5x = 45）和六倍体（2n = 6x = 54）。最常见的减数分裂异常是由于多倍体导致的染色体分离不规则。在几个材料中，以不同频率记录到染色体粘连、异常胞质分裂、中期I的二价体不联会和中期II的染色体以及染色体消除。减数分裂异常的平均百分比范围为0.36%至95.76%。所有这些异常都有可能通过产生不平衡的配子来影响花粉活力。在这些材料中，只有异常率低于40%的四倍体材料适合作为种内和种间杂交的花粉供体。目前，由于缺乏相同倍性水平的雌性有性亲本，高倍性水平（5n和6n）的材料不能用作杂交中的雄性亲本。
