Chaotic spindles causes abnormal chromosome behavior in an interspecific sexual hybrid of Urochloa

Abstract

Intra-and interspeci c hybridization in the genus Urochloa is complex due to apomixis and polyploidy. Such barriers can be overcome by crossing apomictic tetraploid plants as pollen donors with arti cial tetraploid sexual plants as female parents. Another barrier is the incompatibility between the genomes of the different species used in hybridization. Since the meiotic behavior is a good indication of a nity between genomes in a hybrid, the present study analyzed the meiotic behavior of a sexual polyploid interspeci c hybrid of Urochloa from the breeding program at Embrapa Beef Cattle. In addition to the segregational abnormalities associated with polyploidy, cytological studies revealed that, after diakinesis, chromosomes presented an abnormal arrangement in the metaphase plate. In 31.33% of meiocytes, chromosomes were organized into more than one plate, forming up to four metaphase plates. Another abnormality observed in 5.72% of the cells was the lack of convergence of chromosomes to the equatorial plate and consequent abnormal anaphase segregation. These abnormalities led to the formation of several nuclei within the same myocyte then separated by an irregular cytokinesis pattern, forming tetrads with micronuclei, microcytes and polyads. This pattern of behavior seriously compromises the formation of viable gametes, which may later affect the generation of fertile hybrids thus impairing the use of this hybrid as a female parent.