Sanzio Carvalho Lima Barrios

The efficiency of screening tropical forage grass genotypes for waterlogging tolerance under controlled conditions depends on experimental protocols capable of accurately discriminating contrasting genotypes. This study evaluated morphoagronomic and physiological traits of Megathyrsus maximus and Urochloa spp. genotypes subjected to different soil water availabilities to define suitable experimental conditions for waterlogging screening. Two independent experiments were conducted in a randomized complete block design using a 5 × 4 factorial arrangement (five genotypes × four soil water regimes) with four replications, in which morphoagronomic and physiological traits were evaluated. The present study combines previously published data from the 80% and 120% pot water capacity treatments with data from the additional 60% and 100% treatments. Overall, favorable genotype performance was observed around the directly tested 80% of pot water capacity, with greater biomass production, higher numbers of green leaves, higher SPAD index values, and improved photosynthetic performance across several traits and genotypes. In contrast, 120% of pot water capacity caused the greatest reductions in plant growth and physiological activity, allowing clear discrimination between tolerant and susceptible genotypes, whereas 60% and 100% of pot water capacity produced less pronounced effects. The results indicate that approximately 80% of pot water capacity is the most suitable condition for the control treatment, whereas 120% efficiently induces waterlogging stress. This methodological approach provides an experimental basis for standardizing controlled-environment screening assays, improving the reliability of early-stage selection of tropical forage grass genotypes for waterlogging tolerance.

Poorly drained pastures in tropical America are recurrently degraded by Marandu Death Syndrome (MDS), affecting beef and dairy production. This study screened genotypes of Megathyrsus maximus and Urochloa spp. for waterlogging tolerance under controlled conditions to identify discriminant, easily measurable morphoagronomic traits suitable for breeding programs. Four experiments were conducted in factorial arrangement (five genotypes × two water regimes, with four replications), where morphoagronomic and physiological variables were analyzed using multivariate techniques. The first two principal components explained 75.17–88.60% of the total variation and stayed above 70% after variable reduction, without significantly altering genotype dispersion. Physiological responses showed a strong correlation with morphoagronomic traits. The most informative traits were the number of yellow and senescent leaves, number of tillers, SPAD index, leaf dry mass, and root dry mass. Genotypes were grouped by tolerance level. Among M. maximus, ‘Mombaça’ was the most tolerant, while PM13 and PM21 were the least. In Urochloa spp., U. humidicola cv. Tully was the most tolerant and ‘Marandu’ the least tolerant. Screening under controlled conditions is an alternative to distinguish genotypes with contrasting tolerance; however, because controlled environments do not fully reproduce the multifactorial nature of MDS, this approach is recommended only for early stages of breeding programs. Nevertheless, field evaluations on poorly drained soils under grazing remain essential to confirm tolerance to MDS.

Urochloa P. Beauv. (formerly classified as Brachiaria (Trin.) Griseb .) is a genus of African perennial grasses that is extensively cultivated in tropical countries for cattle nutrition. Three of the most economically relevant species, Urochloa brizantha, Urochloa decumbens, and Urochloa ruziziensis, form the brizantha agamic complex, which includes allopolyploid series with distinct subgenomes. Investigating the composition and organization of repetitive DNA, a major component of grass genomes, can provide insights into their genomic relationships and evolutionary history. This study aimed to characterize the repetitive DNA landscape of selected Urochloa species belonging to the b rizantha agamic complex; identify and compare major repeat classes across species; and evaluate their potential as cytogenetic markers on mitotic chromosomes using fluorescent in situ hybridization (FISH). Clustering analysis revealed that repetitive DNA constitutes 56%–65% of the genomes, with Ty3/Gypsy retrotransposons, particularly the Athila and Retand lineages, representing the most abundant repeat class. Urochloa decumbens exhibited the highest proportion of Ty3/Gypsy retrotransposons, while U. ruziziensis had the highest satellite DNA content. The chromosomal location of representative satellites (UroSat-1a, UroSat-2a, and UroSat-3) was determined in all three species via FISH. UroSat-1a was detected in all centromeres, while UroSat-2a and UroSat-3 signals varied in number and position. Our findings validate the use of satDNA as cytogenetic markers in the brizantha agamic complex of Urochloa and revealed genomic relationships among different species and ploidy levels.

Fungi of the genus Pyricularia have a wide range of host plants and are capable of infecting more than 50 species of grasses, causing the blast disease, with damage to the ears. Species of the forage signal grass (Urochloa spp.) can be hosts of this genus of fungus and can be an important source of inoculum of the pathogen for other agricultural crops affected by blast, especially wheat. The objective of this study was to determine the reaction of nine cultivars of Urochloa to the pathogens Pyricularia oryzae Triticum lineage (PoTl), P. pennisetigena, P. urashimae, and P. grisea. The virulence of seven races of PoTl to signal grass cultivars was also evaluated. There was variation in the pathogenicity and virulence of Pyricularia species and PoTl races in different signal grass cultivars. The cultivars Ipyporã, BRS Tupi, and Xaraés were the most resistant to the different blast pathogen species and PoTl races. Therefore, it is recommended to cultivate these varieties in areas adjacent to wheat or in crop-livestock integration.

Key message We present the highest-density genetic map for the hexaploid Urochloa humidicola. SNP markers expose genetic organization, reproduction, and species origin, aiding polyploid and tropical forage research. Abstract Tropical forage grasses are an important food source for animal feeding, with Urochloa humidicola, also known as Koronivia grass, being one of the main pasture grasses for poorly drained soils in the tropics. However, genetic and genomic resources for this species are lacking due to its genomic complexity, including high heterozygosity, evidence of segmental allopolyploidy, and reproduction by apomixis. These complexities hinder the application of marker-assisted selection (MAS) in breeding programs. Here, we developed the highest-density linkage map currently available for the hexaploid tropical forage grass U. humidicola. This map was constructed using a biparental F₁ population generated from a cross between the female parent H031 (CIAT 26146), the only known sexual genotype for the species, and the apomictic male parent H016 (BRS cv. Tupi). The linkage analysis included 4873 single nucleotide polymorphism (SNP) markers with allele dosage information. It allowed mapping of the ASGR locus and apospory phenotype to linkage group 3, in a region syntenic with chromosome 3 of Urochloa ruziziensis and chromosome 1 of Setaria italica. We also identified hexaploid haplotypes for all individuals, assessed the meiotic configuration, and estimated the level of preferential pairing in parents during the meiotic process, which revealed the autopolyploid origin of sexual H031 in contrast to apomictic H016, which presented allopolyploid behavior in preferential pairing analysis. These results provide new information regarding the genetic organization, mode of reproduction, and allopolyploid origin of U. humidicola, potential SNPs markers associated with apomixis for MAS and resources for research on polyploids and tropical forage grasses.

Tropical forage grasses are an important food source for animal feeding, with Urochloa humidicol a, also known as Koronivia grass, being one of the main pasture grasses for poorly drained soils in the tropics. However, genetic and genomic resources for this species are lacking due to its genomic complexity, including high heterozygosity, evidence of segmental allopolyploidy, and reproduction by apomixis. These complexities hinder the application of marker-assisted selection (MAS) in breeding programs. Here, we developed the highest-density linkage map currently available for the hexaploid tropical forage grass U. humidicola . This map was constructed using a biparental F1 population generated from a cross between the female parent H031 (CIAT 26146), the only known sexual genotype for the species, and the apomictic male parent H016 (BRS cv. Tupi). The linkage analysis included 4,873 single nucleotide polymorphism (SNP) markers with allele dosage information. It allowed mapping of the apospory locus and phenotype to linkage group 3, in a region syntenic with chromosome 3 of Urochloa ruziziensis and chromosome 1 of Setaria italica . We also identified hexaploid haplotypes for all individuals, assessed the meiotic configuration, and estimated the level of preferential pairing in parents during the meiotic process, which revealed the autopolyploid origin of sexual H031 in contrast to H016, which presented allopolyploid behavior in preferential pairing analysis. These results provide new information regarding the genetic organization, mode of reproduction, and allopolyploid origin of U. humidicola , potential SNPs markers associated to apomixes for MAS and resources for research on polyploids and tropical forage grasses. Key message: We present the highest-density genetic map for the hexaploid Urochloa humidicola . SNP markers expose genetic organization, reproduction, and species origin, aiding polyploid and tropical forage research.

Urochloa humidicola (Rendle) Morrone & Zuloaga is a species native to Africa that grows in tropical regions, especially in sites with temporary flooding. Despite its importance as forage crop, the karyotypic characterization of its cytotypes remains mainly unfinished, and its polyploid origin is unknown. Therefore, cytogenetic studies can provide information about the evolutionary history of species and to characterize the core and reserve collection of the germplasm banks. We performed the karyotype analyses, mapped ribosomal sites, and estimated genome size, confirming three ploidy levels (6×, 7×, and 9×) and one aneuploid accession H031 (2n = 6× = 36 + 1). Karyotypes are symmetrical and the number of 35S and 5S rDNA sites varied between the cytotypes. However, all sites were at terminal and interstitial positions in the chromosomes, respectively, except one chromosome of the aneuploid accession with interstitial colocalization. The polymorphism of the number and distribution of rDNA sites in U. humidicola was confirmed by (i) the variation between and within plants and in metaphases of the same meristem in hexaploids and heptaploids; (ii) the occurrence of rDNA sites in hemizygosis in all accessions, except heptaploids; (iii) the size heteromorphism in some ribosomal sites of homologous chromosomes. The karyotype data and the mapping of ribosomal sites corroborate the proposals of allopolyploidy in U. humidicola and the hybrid origin to the H031 accession.

The Urochloa spp. breeding program at EMBRAPA‐Brazil targets the development of apomictic hybrids to improve animal performance, while reducing the environmental impact of livestock. In summary, breeders perform multiple crosses between apomictic and sexual parents, and screen progeny to perform selections for agronomic and nutritional traits across several harvests, years and locations. Thus, choosing the right parents and the cross combinations is crucial for the success of the breeding program. The objectives of this study were to: (i) estimate the general (GCA) and specific (SCA) combining ability, and contribution of additive and nonadditive effects, from a partial diallel cross design between three apomictic and ten sexual parents, for agronomical and nutritional traits in Urochloa spp.; (ii) assess genetic gain for all traits by selecting for yield of high nutritional value leaf mass (NLM); (iii) characterize the genotype profiles using genotype by yield*trait (GYT) biplot analysis. A total of 1380 interspecific hybrids from 29 full‐sib progenies were evaluated and then the hybrid selection was performed based on studentized best linear unbiased prediction of NLM. The 10% top‐performing hybrids were used in the GYT analysis using NLM as the basic variable. There was a predominance of nonadditive effects on the phenotypic expression of agronomic and nutritional value traits. The GCA was observed only for some traits in sexual parents, whereas SCA was observed in all traits. The selection based on NLM provided favorable gains for most of the agronomic traits and GYT biplot analysis was efficient to characterize genotype profiles.

Artificial hybridization plays a fundamental role in plant breeding programs since it generates new genotypic combinations that can result in desirable phenotypes. Depending on the species and mode of reproduction, controlled crosses may be challenging, and contaminating individuals can be introduced accidentally. In this context, the identification of such contaminants is important to avoid compromising further selection cycles, as well as genetic and genomic studies. The main objective of this work was to propose an automated multivariate methodology for the detection and classification of putative contaminants, including apomictic clones, self-fertilized individuals, half-siblings and full contaminants, in biparental polyploid progenies of tropical forage grasses. We established a pipeline to identify contaminants in genotyping-by-sequencing (GBS) data encoded as allele dosages of single nucleotide polymorphism (SNP) markers by integrating principal component analysis (PCA), genotypic analysis (GA) measures based on Mendelian segregation and clustering analysis (CA). The combination of these methods allowed the correct identification of all contaminants in all simulated progenies and the detection of putative contaminants in three real progenies of tropical forage grasses, providing an easy and promising methodology for the identification of contaminants in biparental progenies of tetraploid and hexaploid species. The proposed pipeline was made available through the polyCID Shiny app and can be easily coupled with traditional genetic approaches, such as linkage map construction, thereby increasing the efficiency of breeding programs.