1769 RESEARCH B rachiaria (Trin.) Griseb. is a genus belonging to the family Poaceae Barnh., tribe Paniceae Rchb. that aggregates approximately 100 species with considerable forage value and that are native to tropical and subtropical regions of Africa (Keller-Grein et al., 1996).In Brazil, the introduction of the genus began with Brachiaria decumbens Stapf, where its dispersal was favored in several parts of the country. Other species were introduced later, from the 1960s to the mid-1970s, and the genus spread across the Brazilian Cerrado in subsequent years (Mitidieri, 1988).It is estimated that there are 100 million hectares of cultivated pasture and another 70 million hectares of naturalized pasture land in Brazil that are dominated by Brachiaria on approximately 85% of those areas (IBGE, 2006). The species of Brachiaria are arranged in groups according to perceived natural affinities related to the morphology of the inflorescence, especially the spikelet. Two groups of greatest economic importance for the country include: (i) Brachiaria decumbens, Brachiaria brizantha (Hochst. ex A. Rich.) Stapf, and Brachiaria ruziziensis R. Germ. & C.M. Evrard, and (ii) Brachiaria humidicola (Rendle) Schweick., Brachiaria dictyoneura (Fig. and De Not.) Stapf, and Brachiaria jubata (Fig. and De Not.) Stapf (Renvoize et al. , 1996).The taxonomy of the genus is complex due to the continuous variation of traits used to delimit species and related genera ABSTRACT Brachiaria (Trin.) Griseb. is a genus belonging to the Poaceae Barnh. family that aggregates species of forage interest, which have shown different levels of ploidy, intraspecific variability for chromosomal morphology and for number of rDNA sites. This study aimed at characterizing the karyotype of Brachiaria brizantha (Hochst. ex A. Rich) Stapf, Brachiaria decumbens Stapf, and Brachiaria ruziziensis R. Germ. & C.M. Evrard by the location of 5S rDNA, 45S rDNA, centromeric retrotransposons, chromomycin A3 (CMA) and 4¢, 6-diamidino-2-phenylindole dihydrochloride (DAPI) chromosome bands,and transcriptional activity at nucleolar organizing regions (NORs). Brachiaria ruziziensis has 2n = 2x = 18 chromosomes, karyotypic formula 9M, one 45S rDNA site, and two 5S rDNA sites. Brachiaria brizantha has 2n = 4x = 36 chromosomes, karyotypic formula 18M, four to six 5S rDNA signals, and two to four 45S rDNA sites. One of the chromosomes carrying 45S rDNA is heteromorphic. Brachiaria decumbens has 2n = 4x = 36 chromosomes, karyotypic formula 17M+1M/SM, and seven 5S rDNA signals including one hemizygous 5S rDNA locus. One of the two chromosome pairs carrying 45S rDNA signals was heteromorphic with one of its chromosomes possessing a tertiary constriction. Hybridization signals with a centromeric retrotransposon probe, CRM1, were observed in Brachiaria chromosomes with distinct clusters on all B. ruziziensis chromosomes. Chromosomal CMA bands were located along with 45S rDNA signals in B. decumbens and B. ruziziensis whereas in B. brizantha only two out of four signals coincided. The ...

The digestibility potential of leaves from forages depends on the amount of nutrition in their tissues, with low lignin deposition in the cell wall, mainly parenchyma and phloem. This research evaluated the leaf structure of different Urochloa genotypes and discussed its potential for evaluating digestibility. The cultivars U. brizantha, U. decumbens, U. ruziziensis and three clones of U. ruziziensis (1, 95 and 97), which are under development in breeding programs, were evaluated. Plants were grown under the recommended culture conditions for the Urochloa species. Plants were cut 60 days after sowing, and leaves were collected at 15 days of regrowth. Leaves were fixed in FAA 70 and further stored in 70% ethanol until being submitted to the usual microtechniques for the preparation of microscopy slides. The area of the tissues from the interveinal and midrib regions was measured using ImageJ software, and their proportions were calculated. In the interveinal region, the proportion of chlorophyll parenchyma was greater for U. decumbens and the Clone 1 genotypes. Urochloa brizantha and clones 95 and 97 showed a higher proportion of the vascular bundle compared to U. ruziziensis, U. decumbens and Clone 1. The proportion of the ground parenchyma in the midrib was greater in U. brizantha, Clone 95 and Clone 97. Thus, it can be concluded that the Clone 1 genotypes (from U. ruziziensis) showed leaf tissues (parenchyma and phloem) with higher digestibility potential; in addition, U. brizantha and U. decumbens showed a high percentage of xylem and sclerenchyma, which reduces their quality as forage.

Setaria Beauvois, 1812 is a genus of economically important forage species, including Setaria italica (Linnaeus, 1753) Beauvois, 1812 and Setaria viridis (Linnaeus, 1753) Beauvois, 1812, closely related species and considered as model systems for studies of C4 plants. However, complications and uncertainties related to taxonomy of other species of the genus are frequent due to the existence of numerous synonyms for the same species or multiple species with the same name, and overlapping of morphological characteristics. Cytogenetic studies in Setaria can be useful for taxonomic and evolutionary studies as well as for applications in breeding. Thus, this study is aimed at locating 45S and 5S rDNA sites through (FISH)fluorescent in situ hybridization in Setaria italica, Setaria viridis and Setaria sphacelata (Schumacher, 1827) Stapf, Hubbard, Moss, 1929 cultivars (cvs.) Narok and Nandi. Setaria italica and Setaria viridis have 18 chromosomes with karyotype formulas 6m + 3sm and 9m, respectively. The location of 45S and 5S rDNA for these species was in different chromosome pairs among the evaluated species. Setaria viridis presented a more symmetrical karyotype, strengthening the ancestral relationship with Setaria italica. Setaria sphacelata cvs. Narok and Nandi have 36 chromosomes, and karyotype formulas 11m+7sm and 16m+2sm, respectively. The 45S rDNA signals for both cultivars were also observed in distinct chromosome pairs; however chromosomes bearing 5S rDNA are conserved. Karyotypic variations found among the studied species are evidence of chromosomal rearrangements.

Changes in leaf anatomy were evaluated in genotypes of Brachiaria brizantha, Brachiaria decumbens, Brachiaria ruziziensis and three Brachiaria ruziziensis clones through tissue proportion in internerval and midrib regions at three regrowth ages. Plants were grown and cutting was performed after 60 days. Further, leaves were sampled at 8, 15 and 29 regrowth days and processed with usual plant microtechnique. The internerval region showed higher parenchyma percentage at 15 days for Clone 95 and similar values at 15 and 29 days for Clone 1. The proportion of vascular bundles was lower after 15 days in Clones 1 and 95 and 29 days in B. brizantha. In the midrib, the parenchyma proportion was higher at 29 days in B. brizantha and lower at 15 days in B. ruziziensis. The proportion of vascular bundles was higher at 8 days in B. decumbens, B. brizantha and Clone 1, and lower at 29 days for Clones 97 and 95 and at 8 days in B. ruziziensis. Therefore, the regrowth age modifies the percentage of leaf tissues in Brachiaria genotypes, in which the fibers and vascular bundles increase at 29 days and 8-day-old leaves are not fully developed.