Análisis del comportamiento meiótico de híbridos interespecíficos del género Paspalum

The addition of a summer perennial grass to the pasture mixes presents various advantages, such as productivity, seasonal distribution of forage, and resilience, as well as adaptability to climate change. The Dilatata group of the genus Paspalum contains valuable of these grasses with high agronomic potential. Of these species, the most studied has been Paspalum dilatatum var. dilatatum, a pentaploid with apomictic reproduction. This species, despite its high production of dry matter, presents numerous difficulties for its use, such as: low seed production, infection by Claviceps paspali, seed dormancy and slow implantation, as well as difficulties for its improvement. given its apomictic nature. Therefore, a new approach has been carried out in the Faculty of Agronomy, prioritizing the sexual tetraploids of the group (P. flavescens, P. plurinerve, P. vacarianum, P. dasypleurum and P. urvillei), since they present greater possibilities of domestication, due to its sexual breeding system which facilitates genetic improvement. These sexual species are related, have high fertility, high viable seed production, are autogamous and share the genomic formula 2n = 4x = IIJJ, so hybridization among them should be possible. One breeding strategy is interspecific hybridization seeking to combine the best of each species for the formation of a cultigen. In order to carry out an interspecific hybridization program, it is necessary to prove that the available germplasm can be hybridized without decreasing hybrid fertility. As a direct background to this work, a biparental population of recombinant inbred lines (RILs) was previously generated from the cross of P. flavescens x P. plurinerve (both promising species and similar to the "common" genotype in terms of productivity, in addition to presenting differences in terms of flowering date and seed dormancy) using the SSD (single seed descent) method. This previous aim was to evaluate the potential of this breeding method, looking for transgressive segregation, in addition to genotyping and phenotyping the entire collection to identify QTLs associated with domestication characters, such as reduced dormancy. During these efforts, sterility was found in some early lines and a distortion in the segregation of microsatellite-type molecular markers in the F₆. These phenomena may be associated with irregularities in the meiosis of the hybrid, since although related species, they have differences in their genomes. Therefore, in this work, the meiotic behavior of 20 F₂ lines from the interspecific hybridization of P. flavescens x P. plurinerve was analyzed, as well as the degree of fertility of these lines based on seed production. A minimum of 15 pollen mother cells (PMCs) were recorded for diakinesis, metaphase, anaphase, and dyads/tetrads, seeking to detect associations other than bivalents in diakinesis, chromosome advances in metaphase, bridges or delays of chromosomes in anaphase and micronuclei in dyads/tetrads. The results show that 9,5% of the PMCs studied presented irregularities in meiosis, without observing any micronuclei in dyads/tetrads, so that irregularities in early phases of meiosis end up being resolved in later phases. Seed production of the 20 lines ranged from 0% to 63%, with an average of 28% full seeds. No irregularities in meiosis were found to explain the low fertility of some lines. Therefore, meiosis does not explain the sterility in the early lines reported above, nor the distortion in segregation. Other reasons may explain these phenomena, such as genetic control of sterility, that is, there are genes that cause sterility in interspecific hybrids. Molecular cytogenetic techniques like FISH and molecular markers in F₂ lines can determine at what point in inbreeding the distortion in the markers occurs, in addition to describing, using GISH, the bias towards maternal alleles in the chromosomes of F₆ lines.