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Grasses with desirable traits for agriculture and livestock production are continually being sought. The genus Urochloa comprises many species of good forage potential, although studies have mostly focused on commercial cultivars. Karyotype data can be used to characterize species and generate information for taxonomy and evolutionary studies and contribute to breeding programs. The mode of reproduction is also an essential piece of information to determine breeding strategies. This study aimed to characterize the karyotypes of Urochloa arrecta (Hack. ex T. Dur. & Schniz) O. Morrone & F. Zuloaga and a pentaploid cytotype of U. brizantha (Hochst. ex A. Rich.) R. Webster, including the mapping of ribosomal DNA (rDNA) sites and nuclear DNA content and indicating the mode of reproduction. Slides were prepared using the flame drying technique and were subjected to fluorescent in situ hybridization with 35S and 5S rDNA probes. DNA content was estimated by flow cytometry. The classification of the reproduction mode was based on the amplification of the primers N14 and p779/p780. Urochloa arrecta presented 2C = 2.66 pg of DNA, karyotype formula 2n = 4x = 34 m + 2sm, four chromosomes with 35S rDNA sites, and four other chromosomes with 5S rDNA sites. The absence of amplification products with the primers N14 and p779/p780 provided evidence of sexual reproduction. Urochloa brizantha presented 2C = 4.52 pg of DNA and karyotype formula 2n = 5x = 45 m. Five chromosomes presented 35S rDNA, and eight other chromosomes displayed 5S rDNA sites. Polymerase chain reaction results indicated that this cytotype has an apomictic mode of reproduction. The organization of karyotypes suggests an allopolyploid origin for both genotypes. Possible applications of the information found are discussed.

The induction of polyploidy in Eucalyptus can lead to higher-yielding and more adapted clones, with better wood quality. After artificial polyploidization, it is necessary to certify the effectiveness of the process through cytogenetic analyses and anatomical trait evaluations. Thus, the aim of this study was to certify the chromosome duplication in artificially polyploidized clones of Eucalyptus grandis × Eucalyptus urophylla using cytogenetic analysis, flow cytometry, and leaf anatomy measurements. Chromosomal counts and DNA content estimation allowed the identification of artificially polyploidized clones and mixoploids. Polyploid clones had larger stomata diameter than diploids. The increase in stomata size was accompanied by lower stomatal density in most polyploid clones. The typical gigas effect of polyploidized plants was demonstrated by the expressive increase in leaf area in polyploid individuals compared to diploids. Our findings indicate that the use of polyploidy in Eucalyptus breeding is promising, allowing the discrimination of diploid, tetraploid, and mixoploid plants.