Meiotic behavior in early and recent duplicated hexaploid hybrids of napier grass (Pennisetum purpureum) and pearl millet (Pennisetum glaucum)

The production of hybrids between napier grass (Pennisetum purpureum, 2n = 4x = 28, genomes A'A'BB) and pearl millet (P. glaucum, 2n = 2x = 14, genome AA) results in sterile triploid plants. Such sterility of the triploid hybrid creates a hurdle for napier grass breeding programs, since it prevents propagation through seeds. Fertility can be restored by means of chromosome duplication. In most cases, these duplicated Pennisetum hybrids are mixoploids. However, we do not know if there are differences between the meiotic behavior of Pennisetum hybrids between napier grass and pearl millet which were duplicated early on and those duplicated more recently. This work evaluated the meiotic behavior and the pollen viability of American and Brazilian hexaploid hybrids, which differ by about 25 years in duplication time. In all analyzed hybrids, irregularities were observed from the initial phases of meiosis to pollen grain production, independently from the time elapsed for the duplication induction. The most frequent meiotic abnormalities are related to chromosome segregation due to irregular pairing. These irregularities will directly affect the viability and the size of the pollen grains.