Análise do comportamento meiótico e modo de reprodução de acessos de Urochloa dictyoneura (Fig. & De Not.) Veldkamp e Urochloa humidicola (Rendle) Morrone & Zuloaga (Poaceae)

Abstract

Urochloadictyoneura and U. humidicola stand out for adapting in flooded and acid soils and having tolerance to spittlebugs. Such attributes are advantageous in cultivating these plants in grazing areas with diverse edaphoclimatic characteristics and have made these species attractive for genetic improvement programs.The generation of intra or interspecific hybrids is one of the approaches used in plant breeding to obtain genotypes with agronomic characteristics superior to the parental ones. However, knowledge of meiotic behavior, ploidy level, type of polyploidy and reproduction mode is pivotal to obtaining better results and successful crosses. Urochloadictyoneura and U. humidicola form an agamic complex constituted by polyploidcytotypes that present high rates of meiotic abnormalities and predominance of apomixis. Thus, in order to understand the aspects that involve these taxa, the present study aimed to evaluate the meiotic behavior and pollen viability and confirm the mode of reproduction of two accessions tetraploid and nonaploid of U. dictyoneura and one accession heptaploid of U. humidicola. Slides were prepared by the squash technique. The meiocyteswere stained with 1% propionic carmine, and the pollen grains with Alexander dye. The mode of reproduction was identified via PCR with the primer p779/p780, which amplifies the specific genomic region of the apospory (ASGR-BBML). Bivalent, univalent and multivalent pairing configurations were observed in pollen grain mother cells (PMCs) of the three accessions, but with the predominance of bivalent (II) in U. dictyoneura (4x and 9x). The interaction involving more than two chromosomes and the formation of univalent resulted in irregular orientations and segregations and micronuclei formation in prophases, telophases and tetrads. In addition, asynchrony was observed in prophase II, metaphase II and anaphase II. The tetraploid, heptaploid and nonaploid accessions showed, respectively, meiotic index of 59,33%, 25,33% and 80%, and pollen viability 39,20%, 78,90% and 0%. Apomixiswas confirmed in the three accessions evaluated. The inclusion of more cytotypes and the performance of other studies aimed at the cytogenetic characterization of the ‘humidicola’ complex is of great interest in manipulating of the germplasm available to support the efforts of genetic breeding.