Abnormal meiotic behavior in Brachiaria brizantha (Poaceae) leading to microspore degeneration

摘要

The current paper reports an original abnormality recorded in one accession of Brachiaria brizantha (B003) of the Brazilian germplasm collection for the genus Brachiaria maintained at Embrapa Beef Cattle. Among 25 inflorescences analyzed, 15 presented an abnormality affecting several phases of microsporogenesis. The abnormality appeared after nucleolus disintegration at diakinesis and was recorded till the end of meiosis. In affected inflorescences, bivalents were not able to congregate in a metaphase plate, remaining scattered or sometimes grouped in the cytoplasm. They then gave rise to pycnotic nuclei of different sizes that were later rejoined into telophase nuclei allocated peripherically. Anaphases I were never seen. After the first cytokinesis, the meiocytes entered meiosis II In prophase II, nuclei presented abnormal positions. In metaphase II, once more, metaphase plates were not observed and chromosomes were grouped into two small and pycnotic nuclei sometimes irregularly located. From telophase II, independently of nuclei position, some meiocytes under-went the second cytokinesis, but the majority of meiotic products was characterized by dyads. Independently of the origins, microspores degenerated as soon as they were released, acquiring irregular shapes, and becoming intensely stained. At the end, nuclei degenerated and microspores gave rise to an amorphous mass. Pollen grains were not found in the affected inflorescences. The importance of this abnormality for Brachiaria breeding is discussed.