Citogenética e análise genômica em Urochloa humidicola (Rendle) Morrone & Zuloaga

Abstract

Urochloa humidicola is among the most widely used forage grasses in Brazil, standing out for its adaptation to poor soils and areas subject to temporary flooding. The U. humidicola germplasm is predominantly composed of apomictic polyploids, with only the H031 accession described as sexual. This genotype presents controversies regarding its origin and genomic composition and was recently characterized as aneuploid (2n = 6x = 36 + 1). This accession has been used as the female parent in crosses with hexaploid apomictic plants of U. humidicola, such as the cultivar BRS Tupi (H016; 2n = 6x = 36).The present study aimed to: (1) comparatively evaluate meiosis and the mode of reproduction of the aneuploid and euploid parental accessions and their respective hybrids, in addition to determining the chromosome number and genome size of the hybrids; and (2) investigate the genomic relationships among the accessions H031, H016, and Dt158 of U. dictyoneura (all belonging to the Humidicola clade), as well as with three diploid species from the Brizantha clade, by applying genomic in situ hybridization (GISH).The hybrids presented 2n = 6x = 36 chromosomes and a smaller genome size. The p779/p780 marker confirmed only the H016 accession as apomictic. Meiotic analysis revealed a lower frequency of irregularities in the euploid accession H016, whereas the hybrids showed high rates of univalents and multivalents, reflecting the genomic differences between the parents. GISH using genomic DNA from diploids of the Brizantha clade and between accessions H031 and H016 enabled the discrimination of differences between the genomes that compose the hexaploid accessions. The U. dictyoneura 4x probe did not allow the discrimination of subgenomes in U. humidicola. The genome of the diploid species from the Brizantha clade (B1B 1 or B2B 2 ) is ancestral to the hexaploids of U. humidicola (H031 and H016). These accessions also present homeologous genomes, here designated A and A′, and have been characterized as autoallopolyploid.