Performance de híbridos simples de milho desenvolvidos de populações melhoradas por seleção recorrente recíproca modificada

Maize (Zea mays L.) elite inbred lines developed from pedigree programs tend to be genetically related. Therefore, it is necessary to incorporate unrelated inbreds to those programs to allow the continued release of outstanding single-crosses. The objectives of this research were to compare the usefulness of a modified reciprocal recurrent selection procedure (MRRS) to improve populations to be used as sources of elite inbreds and outstanding single-crosses to integrate pedigree programs, and to investigate the effects of selection on the relative contribution of general (GCA) and specific combining (SCA) abilities to the single-crosses variation. Eight and six S3 lines from populations IG-3-C1 and IG-4-C1, respectively, selected from the first cycle of the MRRS program were crossed in a partial-diallel mating design, and the 48 experimental and five commercial single-crosses were evaluated in six environments. Grain yield mean of the experimental single-crosses (9.57 t ha¹) did not differ from the commercial single-crosses (9.86 t ha¹), and ten of the 48 experimental single-crosses could be released as cultivars because they compared favorably to the currently used single-crosses. Thus, one cycle of the MRRS procedure improved efficiently the populations allowing the development of outstanding single-cross, but additional cycles of selection should be carried out since none of the experimental single-crosses outperformed the highest yielding commercial single-cross. The relative contribution of the GCA over SCA may have been affected by the MRRS, since the SCA was more important than GCA for some of the traits assessed.Linhagens elites de milho (Zea mays L.) desenvolvidas em programas genealógicos tendem a ser geneticamente relacionadas. Portanto, é necessário incorporar linhagens não relacionadas a estes programas para permitir a liberação contínua de híbridos simples superiores. Comparou-se a utilidade de um procedimento modificado de seleção recorrente recíproca (SRRM) em melhorar populações a serem utilizadas como fontes de linhagens elites e híbridos simples superiores para integrar os programas de melhoramento, e investigar os efeitos da seleção na contribuição relativa da capacidade geral (CGC) e da capacidade específica (CEC) de combinação para a variabilidade dos híbridos simples. Oito e seis linhagens S3 obtidas das populações IG-3-C1 e IG-4-C1, respectivamente, selecionadas do primeiro ciclo de SRRM, foram cruzadas no delineamento dialelo parcial e os 48 híbridos simples experimentais (HSE) e cinco híbridos simples comerciais (HSC) foram avaliados em seis ambientes. A média geral de produção de grãos dos HSE (9.57 t ha¹) não diferiu significativamente dos HSC (9.86 t ha¹), e dez dos 48 HSE poderiam ser liberados como cultivares, pois são comparáveis aos híbridos simples comerciais. Portanto, um ciclo de SRRM foi eficiente em melhorar as populações permitindo a produção de híbridos simples superiores, mas ciclos adicionais de seleção deverão ser conduzidos, pois nenhum dos HSE superou o híbrido simples comercial mais produtivo. As contribuições relativas da CGC e da CEC podem ter sido afetadas pela SRRM, uma vez que a CEC foi mais importante que a CGC para alguns caracteres avaliados

Genetic Mapping With Allele Dosage Information in Tetraploid Urochloa decumbens (Stapf) R. D. Webster Reveals Insights Into Spittlebug (Notozulia entreriana Berg) Resistance

Urochloa decumbens (Stapf) R. D. Webster is one of the most important African forage grasses in Brazilian beef production. Currently available genetic-genomic resources for this species are restricted mainly due to polyploidy and apomixis. Therefore, crucial genomic-molecular studies such as the construction of genetic maps and the mapping of quantitative trait loci (QTLs) are very challenging and consequently affect the advancement of molecular breeding. The objectives of this work were to (i) construct an integrated U. decumbens genetic map for a full-sibling progeny using GBS-based markers with allele dosage information, (ii) detect QTLs for spittlebug (Notozulia entreriana) resistance, and (iii) seek putative candidate genes involved in defense against biotic stresses. We used the Setaria viridis genome a reference to align GBS reads and selected 4,240 high-quality SNP markers with allele dosage information. Of these markers, 1,000 were distributed throughout nine homologous groups with a cumulative map length of 1,335.09 cM and an average marker density of 1.33 cM. We detected QTLs for resistance to spittlebug, an important pasture insect pest, that explained between 4.66 and 6.24% of the phenotypic variation. These QTLs are in regions containing putative candidate genes related to defense against biotic stresses. Because this is the first genetic map with SNP autotetraploid dosage data and QTL detection in U. decumbens, it will be useful for future evolutionary studies, genome assembly, and other QTL analyses in Urochloa spp. Moreover, the results might facilitate the isolation of spittlebug-related candidate genes and help clarify the mechanism of spittlebug resistance. These approaches will improve selection efficiency and accuracy in U. decumbens molecular breeding and shorten the breeding cycle

QTL by environment interaction for grain yield and its components in a tropical maize population

A interação QTL por ambientes (QE) têm sido relatada como uma das principais causas de insucesso da seleção assistida por marcadores moleculares (SAM). Estudos que visam o melhor entendimento da interação QE podem contribuir para o aumento da eficiência dos programas de SAM. O objetivo deste trabalho foi mapear QTL para produção de grãos (PG), prolificidade (PROL), peso de 500 grãos (P500), comprimento (CE) e diâmetro de espiga (DE), profundidade de grão (PROF), número de fileiras (NFil) e de grãos por fileira (NGFil) em uma população de milho tropical, verificar a importância da interação QE para estes caracteres e avaliar a estabilidade dos efeitos genéticos dos QTL mapeados. Uma população de 256 progênies F2:3 obtida do cruzamento entre duas linhagens de grupos heteróticos distintos e contrastantes para diversos caracteres foi avaliada em 13 ambientes. Os ambientes foram alocados em grupo de ambientes utilizando um método de agrupamento e o modelo AMMI, sendo que ambos os métodos levaram a identificação de três grupos de ambientes. O mapeamento de QTL foi realizado considerando um mapa genético com 177 marcadores microssatélites e mapeamento por intervalo composto expandido para múltiplos ambientes (mCIM). As médias de grupo de ambientes para cada caráter foram utilizadas nas análises. Foram mapeados 87 QTL, sendo 9 para PG, 9 para PROL, 14 para P500, 7 para CE, 9 para DE, 14 para PROF, 17 para NFil e 8 para NGFil. A maioria dos QTL mapeados localizou-se em regiões genômicas que ainda não foram reportados QTL, tanto para germoplasma temperado quanto tropical. A interação QTL por grupo de ambientes foi significativa para PG e não significativa para os componentes de produção. Para PG, as metodologias QQE biplot e AMMI foram utilizadas para estudar a interação QE dos efeitos genéticos dos QTL. As estimativas dos efeitos aditivos e de dominância dos QTL foram influenciadas pela interação QTL por grupo de ambientes, sendo que o padrão de interação foi específico para cada efeito genético. A expressiva interação QTL por grupo de ambientes para PG e o padrão específico de interação dos efeitos genéticos dos QTL impõe desafios adicionais à incorporação da SAM nos programas de melhoramento que visam o desenvolvimento de genótipos produtivos e com estabilidade de produção.QTL by environment (QE) interaction has been reported as one of the main reasons for the unsuccessful of marker-assisted selection (MAS). Studies aimed to a better understanding of QE interaction could contribute to increase the efficiency of MAS programs. The objectives of this study were to map QTL for grain yield (GY), prolificacy (PROL), 500 Kernels weight (W500), ear length (EL), ear diameter (ED), kernel depth (KD), row number per ear (RN) and kernels per row number (KRN) in a tropical maize population, to assess the importance of QE interaction for these traits and to evaluate the stability of the genetic effects of mapped QTL. A population of two-hundred and fifty-six progenies obtained from the cross between two inbred lines, which belong to different heterotic groups and divergent for different traits, was evaluated in 13 environments. The environments were jointed into groups using a cluster method and an AMMI model. Both methods led to the identification of three groups of environments. The QTL mapping was performed considering a genetic map with 177 microsatellites markers and the multiple-environment composite interval mapping analysis (mCIM). The means from each group of environments of each trait were used in the analyses. Eighty seven QTL were mapped: 9 for GY, 9 for PROL, 14 for W500, 7 for EL, 9 for ED, 14 for KD, 17 for RN and 8 for KRN. Most of the mapped QTL was located in genomic regions that have not been reported QTL in both temperate and tropical germplasm. The QTL by group of environments interaction was significant for GY and not significant for yield components. For GY, QQE biplot and AMMI methodologies were used to study the QE interaction of the genetic effects of the QTL. The estimates of additive and dominance effects of QTL were affected by QTL by group of environments interaction and the interaction pattern was specific for each genetic effect. The large QTL by group of environments interaction for GY and the specific interaction pattern of the genetic effects of QTL impose additional challenges for the incorporation of MAS in breeding programs that aim to develop high yielding genotypes with grain yield stability

Brachiaria decumbens intraspecific hybrids: characterization and selection for seed production

Abstract: Brachiaria decumbens has great importance in the national beef cattle scenario due to its high forage yield potential and high adaptability to acid soils and low fertility. In order to obtain new cultivars, intraspecific hybrids, previously selected by the Brachiaria breeding program, were evaluated in 2013 and 2014 for phenological characteristics and seed production potential through their production components, aiming to obtain cultivars with satisfactory production agronomic characteristics and forage yield, resistant to 'cigarrinhas-das-pastagens'(Tomaspia sp.) and good seed production. Estimates of phenotypic correlation and analysis of variance were performed using the SAS 9.3 software. From the results obtained in both consecutive years, it was observed that there was a correlation between the reproductive tiller number (RT) and the pure seeds (PS) weight in the seedbeds of the second year of production around 70% (p < 0.01), which can be considered as a parameter to estimate the production of pure seeds before the start of flowering

Brachiaria decumbens intraspecific hybrids: characterization and selection for seed production

Abstract: Brachiaria decumbens has great importance in the national beef cattle scenario due to its high forage yield potential and high adaptability to acid soils and low fertility. In order to obtain new cultivars, intraspecific hybrids, previously selected by the Brachiaria breeding program, were evaluated in 2013 and 2014 for phenological characteristics and seed production potential through their production components, aiming to obtain cultivars with satisfactory production agronomic characteristics and forage yield, resistant to 'cigarrinhas-das-pastagens'(Tomaspia sp.) and good seed production. Estimates of phenotypic correlation and analysis of variance were performed using the SAS 9.3 software. From the results obtained in both consecutive years, it was observed that there was a correlation between the reproductive tiller number (RT) and the pure seeds (PS) weight in the seedbeds of the second year of production around 70% (p < 0.01), which can be considered as a parameter to estimate the production of pure seeds before the start of flowering

Characterization and selection of interspecific hybrids of Brachiaria decumbens for seed production in Campo Grande - MS

Abstract The breeding program Brachiaria developed by Embrapa Beef Cattle provides studies to obtain forage with agronomic characters desired by farmers. In this regard, in 2013 and 2014, a study was carried out in order to select the best Brachiaria decumbens intraspecific hybrids, which are superior in relation to production, forage nutritional value, and resistance to spittlebugs. Estimates of genetic parameters and gains with selection were carried out. It was found that there was significant variability between genotypes for all characters. Gain with selection (GS%) ranged from 12 to 324%, and the highest percentage was found for weight of pure seeds (PS) of seed collectors of the second harvest. For reproductive tillers (RT), C001 and R091 hybrids had better performance than the control, and this character may be considered as a parameter to estimate production of pure seeds before flowering starts

Estimate of genetic parameters in Brachiaria decumbens hybrids Estimate of genetic parameters in Brachiaria decumbens hybrids ARTICLE

weight (FGW); total dry matter (TDM); speed of regrowth (SR); tiller regrowth density (TRD); regrowth ability (REG); crude protein (CP); in vitro organic matter digestibility (IVD); neutral detergent fiber (NDF) and lignin (LIG). The statistical analyses were carried out using the mixed models methods. Genetic variability for all traits assessed was detected, and estimates of individual heritability were of medium to high magnitude, indicating the possibility of gains with selection. Significant genetic correlations were observed betwee

Estimate of genetic parameters in Brachiaria decumbens hybrids

The objective of this study was to estimate genetic parameters for agronomic traits and nutritional value in intraspecific hybrids of B. decumbens. For this, a population of 1,415 hybrids was evaluated in field plots at Embrapa Beef Cattle in Campo Grande/MS/Brazil, with seven clippings in order to estimate field green weight (FGW); total dry matter (TDM); speed of regrowth (SR); tiller regrowth density (TRD); regrowth ability (REG); crude protein (CP); in vitro organic matter digestibility (IVD); neutral detergent fiber (NDF) and lignin (LIG). The statistical analyses were carried out using the mixed models methods. Genetic variability for all traits assessed was detected, and estimates of individual heritability were of medium to high magnitude, indicating the possibility of gains with selection. Significant genetic correlations were observed between FGW and TDM (0.99), TDM and SR (0.81), TDM and IVD (-0.71), TDM and LIG (0.71), and CP and IVD (0.70)

Genetic parameters and selection of Brachiaria decumbens hybrids for agronomic traits and resistance to spittlebugs

Abstract The objective of this work was to estimate genetic parameters for agronomic traits and resistance to spittlebugs in B. decumbens hybrids and to select the ones with best performance. For that, 324 hybrids were evaluated in field plots for agronomic traits and in the greenhouse for resistance to spittlebugs. Genetic variability amongst the hybrids was observed for all traits analyzed. The heritability estimates between genotypes means were higher than 0.52 for all agronomic traits and 0.98 and 0.99 for nymphal survival and nymphal period duration respectively. Hybrids with better performance than cultivar Basilisk for each individual trait were identified and also through a selection index combining all traits. Assigning weights to the different traits in the selection index did not significantly alter the rank for superior hybrids. Those were selected to continue on to the next phases of the breeding program

Data from: Expected genotype quality and diploidized marker data from genotyping-by-sequencing of Urochloa spp. tetraploids

Although genotyping-by-sequencing (GBS) is a well-established marker technology in diploids, the development of best practices for tetraploid species is a topic of current research. We determined the theoretical relationship between read depth and the phred-scaled probability of genotype misclassification, conditioned on the true genotype, which we call Expected Genotype Quality (EGQ). If the GBS method has 0.5% allelic error, then 17 reads are needed to classify simplex tetraploids as heterozygous with 95% accuracy (EGQ = 13) compared with 61 reads to determine allele dosage. We developed an R script to convert tetraploid GBS data in Variant Call Format (VCF) into diploidized genotype calls and applied it to 267 interspecific hybrids of the tetraploid forage grass Urochloa (syn. Brachiaria). When reads were aligned to a mock reference genome created from GBS data of the U. brizantha cultivar ‘Marandu’, 25,678 bi-allelic SNPs were discovered, compared to approximately 3000 SNPs when aligning to the closest true reference genomes, Setaria viridis and S. italica. Cross-validation revealed that missing genotypes were imputed by the Random Forest method with a median accuracy of 0.85, regardless of heterozygote frequency. Using the Urochloa spp. hybrids, we illustrated how filtering samples based only on GQ creates genotype bias; a depth threshold based on EGQ is also needed, regardless of whether genotypes are called using a diploidized or allele dosage model