Microsporogenesis in Brachiaria  brizantha (Poaceae) as a selection tool for breeding.
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.
Departamento de Biologia Celular e Genética, Universidade Estadual de Maringá, Maringá, PR, Brasil. mspagliarini@uem.br
M S
MS
Pagliarini
C B
CB
Valle
E M
EM
Santos
D V
DV
Mendes
Z H
ZH
Bernardo
A B
AB
Mendes-Bonato
N
N
Silva
V
V
Calisto
D035201:Brachiaria / Q000166:cytology / Q000235:genetics* / Q000502:physiology*; D001947:Breeding / Q000379:methods*; D032461:Chromosomes, Plant / Q000235:genetics; D056130:Gametogenesis, Plant / Q000235:genetics / Q000502:physiology*; D008677:Metaphase / Q000235:genetics