Comparative microsporogenesis between diploid and tetraploid plants of Brachiaria ruziziensis and their progenies

Microsporogenesis studies in Brachiaria have been concentrated in the species B. ruziziensis, B. decumbens and B.brizantha and hybrids because they have great importance as forage. Besides the sexual behavior, B. ruziziensis is among a minority of Brachiaria diploid species (2n = 2 × = 18), while most are tetraploid (2n= 4 × = 36) and apomictic. Brachiaria ruziziensis is used in intra and interspecific crossbreedings. For the success of interspecific hybridization, artificial tetraploidization of B. ruziziensis is necessary. The aim of this study was to compare the microsporogenesis in diploid and synthetic tetraploid B. ruziziensis plants and their respective progenies. The slides were prepared by squash technique and stained with 1% propionic carmine for meiocyte analysis and Alexander's stain for pollen viability. Abnormalities were found in all phases of meiosis in the families of the diploid and tetraploid plants and, in general, the rate was considered low, with the percentage varying according to the genotypes. The diploid family was considered more stable. For both families, there is a tendency to reduce the total frequency of abnormalities in the progenies compared to the mother plants. This response indicates that combinations of random crosses or self-fertilization among plants with the same ploidy level were favorable. For the diploid accessions, the pollen viability index was high, reaching up to 88.3%, whereas the tetraploidized plants presented lower values, reaching a maximum of 61.1%. The results will be of interest to researchers involved in tropical forage breeding or conducting intraspecific crosses, since the occurrence of regular meiosis in progenies ensures the formation of viable pollen grains.