Genome-wide association analysis of ear rot resistance caused by Fusarium verticillioides in maize.

The identification of causal regions associated with resistance to Fusarium verticillioides can be useful to understand resistance mechanisms and further be used in breeding programs. In this study, a genome-wide association study (GWAS) was conducted to identify candidate markers associated with resistance to the ear rot caused by the fungus F. verticillioides. A total of 242 maize inbred lines were genotyped with 23,153 DArT-seq markers. A total of 12 DArTs were associated with ear rot resistance. Some DArTs were localized close to genes with functions directly related to ear rot resistance, such as a gene responsible for the innate immune response that belongs to the class of NBS-LRR receptors. Some markers were also found to be closely associated with genes that synthesize transcription factors (nactf11 and nactf61), genes responsible for the oxidation-reduction process and peroxidase activity. These results are encouraging since some candidate markers can present functional relationship with ear rot resistance in maize.

Genomic selection to resistance to Stenocarpella maydis in maize lines using DArTseq markers.

BACKGROUND: The identification of lines resistant to ear diseases is of great importance in maize breeding because such diseases directly interfere with kernel quality and yield. Among these diseases, ear rot disease is widely relevant due to significant decrease in grain yield. Ear rot may be caused by the fungus Stenocarpella maydi; however, little information about genetic resistance to this pathogen is available in maize, mainly related to candidate genes in genome. In order to exploit this genome information we used 23.154 Dart-seq markers in 238 lines and apply genome-wide selection to select resistance genotypes. We divide the lines into clusters to identify groups related to resistance to Stenocarpella maydi and use Bayesian stochastic search variable approach and rr-BLUP methods to comparate their selection results. RESULTS: Through a principal component analysis (PCA) and hierarchical clustering, it was observed that the three main genetic groups (Stiff Stalk Synthetic, Non-Stiff Stalk Synthetic and Tropical) were clustered in a consistent manner, and information on the resistance sources could be obtained according to the line of origin where populations derived from genetic subgroup Suwan presenting higher levels of resistance. The ridge regression best linear unbiased prediction (rr-BLUP) and Bayesian stochastic search variable (BSSV) models presented equivalent abilities regarding predictive processes. CONCLUSION: Our work showed that is possible to select maize lines presenting a high resistance to Stenocarpella maydis. This claim is based on the acceptable level of predictive accuracy obtained by Genome-wide Selection (GWS) using different models. Furthermore, the lines related to background Suwan present a higher level of resistance than lines related to other groups.

Use of the reversible jump Markov chain Monte Carlo algorithm to select multiplicative terms in the AMMI-Bayesian model.

The model selection stage has become a central theme in applying the additive main effects and multiplicative interaction (AMMI) model to determine the optimal number of bilinear components to be retained to describe the genotype-by-environment interaction (GEI). In the Bayesian context, this problem has been addressed by using information criteria and the Bayes factor. However, these procedures are computationally intensive, making their application unfeasible when the model's parametric space is large. A Bayesian analysis of the AMMI model was conducted using the Reversible Jump algorithm (RJMCMC) to determine the number of multiplicative terms needed to explain the GEI pattern. Three a priori distributions were assigned for the singular value scale parameter under different justifications, namely: i) the insufficient reason principle (uniform); ii) the invariance principle (Jeffreys' prior) and iii) the maximum entropy principle. Simulated and real data were used to exemplify the method. An evaluation of the predictive ability of models for simulated data was conducted and indicated that the AMMI analysis, in general, was robust, and models adjusted by the Reversible Jump method were superior to those in which sampling was performed only by the Gibbs sampler. In addition, the RJMCMC showed greater feasibility since the selection and estimation of parameters are carried out concurrently in the same sampling algorithm, being more attractive in terms of computational time. The use of the maximum entropy principle makes the analysis more flexible, avoiding the use of procedures for correcting prior degrees of freedom and obtaining improper posterior marginal distributions.

Bayesian mapping of multiple traits in maize: the importance of pleiotropic effects in studying the inheritance of quantitative traits.

Pleiotropy has played an important role in understanding quantitative traits. However, the extensiveness of this effect in the genome and its consequences for plant improvement have not been fully elucidated. The aim of this study was to identify pleiotropic quantitative trait loci (QTLs) in maize using Bayesian multiple interval mapping. Additionally, we sought to obtain a better understanding of the inheritance, extent and distribution of pleiotropic effects of several components in maize production. The design III procedure was used from a population derived from the cross of the inbred lines L-14-04B and L-08-05F. Two hundred and fifty plants were genotyped with 177 microsatellite markers and backcrossed to both parents giving rise to 500 backcrossed progenies, which were evaluated in six environments for grain yield and its components. The results of this study suggest that mapping isolated traits limits our understanding of the genetic architecture of quantitative traits. This architecture can be better understood by using pleiotropic networks that facilitate the visualization of the complexity of quantitative inheritance, and this characterization will help to develop new selection strategies. It was also possible to confront the idea that it is feasible to identify QTLs for complex traits such as grain yield, as pleiotropy acts prominently on its subtraits and as this "trait" can be broken down and predicted almost completely by the QTLs of its components. Additionally, pleiotropic QTLs do not necessarily signify pleiotropy of allelic interactions, and this indicates that the pervasive pleiotropy does not limit the genetic adaptability of plants.

Inclusion of Dominance Effects in the Multivariate GBLUP Model.

New proposals for models and applications of prediction processes with data on molecular markers may help reduce the financial costs of and identify superior genotypes in maize breeding programs. Studies evaluating Genomic Best Linear Unbiased Prediction (GBLUP) models including dominance effects have not been performed in the univariate and multivariate context in the data analysis of this crop. A single cross hybrid construction procedure was performed in this study using phenotypic data and actual molecular markers of 4,091 maize lines from the public database Panzea. A total of 400 simple hybrids resulting from this process were analyzed using the univariate and multivariate GBLUP model considering only additive effects additive plus dominance effects. Historic heritability scenarios of five traits and other genetic architecture settings were used to compare models, evaluating the predictive ability and estimation of variance components. Marginal differences were detected between the multivariate and univariate models. The main explanation for the small discrepancy between models is the low- to moderate-magnitude correlations between the traits studied and moderate heritabilities. These conditions do not favor the advantages of multivariate analysis. The inclusion of dominance effects in the models was an efficient strategy to improve the predictive ability and estimation quality of variance components.

Índice de seleção e estimativa de parâmetros genéticos e fenotípicos para características relacionadas com a produção de milho-verde / Index of selection and estimation of genetic and phenotypical parameters for traits related with the production of vegetable corn

O Brasil é um dos maiores produtores de milho do mundo e possui grande potencial para a produção de milho verde. Além de agregar valor ao produto, a comercialização de milho verde cresceu muito nos últimos anos. Há escassez de informações sobre a avaliação e a obtenção de cultivares destinadas à produção de milho-verde e também sobre estudos genéticos das características envolvidas nessa produção. Objetivou-se, neste trabalho, estimar parâmetros genéticos e fenotípicos, a correlação genética, classificar e identificar híbridos de milho verde promissores ao mercado consumidor e avaliar a eficiência dos pesos econômicos atribuídos. Os resultados determinaram que a seleção terá sucesso, para as diferentes características de milho-verde, pois, a herdabilidade foi de alta magnitude para as características avaliadas. A avaliação da produtividade de espigas empalhadas (PEE) é suficiente para definir quais os híbridos apresentam o melhor desempenho para a produtividade de espigas comerciais (PEC), diâmetro (DIAM) e comprimento de espigas (COMP). Isso indica que as características PEC, DIAM e COMP podem ser descartadas da avaliação em programas de melhoramento de milho-verde. Os híbridos HS48, HS27, HS24, HS25, HS12 e HS45 acumularam um maior número de características desejadas em um único genótipo, com base no índice de seleção baseado na soma de postos, sendo os mais promissores para a produção de milho-verde. Os pesos econômicos utilizados foram capazes de distinguir e identificar os híbridos mais promissores para a produção de milho- verde e podem ser utilizados como critério de seleção em programas de melhoramento de milho-verde.

Brazil is one of the largest producers of corn of the world and it possesses great potential for vegetable corn production. Besides adding value to the product, the commercialization of vegetable corn increased in the last years. There is shortage of information about the evaluation and the acquisition of genotypes destined to the production of vegetable corn and also on genetic studies of the traits involved in this production. The objective of this work was to estimate the genetic and phenotypic parameters, and the genetic correlation, and to classify and identify hybrids of promising vegetable corn to the consumer market and to evaluate the efficiency of the attributed economical weights. The results determined that the selection will succeed, for the different traits of vegetable corn, because the heritability was of high magnitude to the appraised traits. Evaluation of husked ears yield (PEE) was enough to define which hybrid presents better commercial ear productivity, diameter and corn ear length. This indicates that those traits could be discarded in the selection process of genotypes of breeding programs for vegetable corn production. The hybrids HS48, HS27, HS24, HS25 and HS12 accumulated the largest number of desirable traits in a single genotype based on the sum of rank index. The used economical weights were efficient to distinguish and identify the most promising hybrid for vegetable corn production and they can be used as a selection criterion in programs of breeding of vegetable corn.

Qualidade sanitária de grãos de milho com e sem inoculação a campo dos fungos causadores de podridões de espigaspiga / Sanitary quality of corn grains with and without in-field inoculation with corn ear rot causing fungi

O uso sucessivo de híbridos de milho com resistência variada aos fungos causadores de podridão de grãos tem causado aumento na importância dessas doenças a cada safra. Conduziu-se este trabalho com o objetivo de avaliar pelo teste de sanidade (blotter test) a severidade do fungo Fusarium verticilioides e a incidência dos fungos Stenocarpella maydis e Stenocarpella macrospora em grãos de milho, oriundos de híbridos comerciais, com e sem a inoculação artificial a campo, em dois sistemas de cultivo, convencional e sistema de semeadura direta e em dois anos agrícolas. O experimento foi conduzido a campo, em blocos casualizados, com três repetições. Em laboratório, foram avaliadas, pelo método de "blotter test", a severidade do fungo F. verticilioides e a incidência dos fungos S. maydis e S. macrospora causadores de podridões de espiga. A avaliação pelo teste de sanidade (blotter test) evidenciou a diferença entre os híbridos quanto a reação aos fungos F.verticilioides, S. maydis e S. macrospora. Houve influência do híbrido, da safra agrícola e do sistema de cultivo sobre a infecção dos fungos causadores de podridões de espigas, sendo que o sistema plantio direto favorece o aumento dos fungos responsáveis pelos grãos ardidos em milho. A utilização da inoculação artificial, em campo, visando a selecionar genótipos resistentes aos fungos causadores do "complexo de grãos ardidos" é eficiente.

The continued use of corn hybrids with varied resistance to grain rot-causing fungal agents increases the importance of these diseases every year. The objective of this work was to evaluate, by a sanitary test (blotter test), the severity of the fungus Fusarium verticilioides and the incidence of Stenocarpella maydis and Stenocarpella macrospora in corn grain from commercial hybrids, with and without in-field artificial inoculation, under two cultivation systems (conventional and direct sowing), over two crop seasons. The experiment was carried out under field conditions, using an experimental randomized blocks design, with three replications. In the laboratory, the severity of F. verticilioides and the incidence of S. maydis and S. macrospora ,the causative agents of ear rot in corn, were evaluated by the "blotter test" method. The blotter test evaluation allowed us to detect differences between the hybrids in their reactions to the fungi F. verticilioides, S. maydis and S. macrospora. The crop season and cultivation system used had the most influence on fungal infection in the hybrids. The direct sowing system showed an increase in the fungal infection responsible for causing grain rot. The use of artificial inoculation, in-field, to select genotypes resistant to the fungal agents causing the "grain rot complex" is efficient.

Índice de cobertura vegetal pela cultura do milho no período de chuvas intensas no sul de Minas Gerais / Plant cover index in the period of intensive rainfall for corn crop at south of Minas Gerais state, Brazil

A cobertura vegetal é a defesa natural do solo contra a erosão hídrica. Nos modelos de estimativas de perdas de solo, o efeito da cobertura vegetal na interceptação da energia cinética da chuva é a variável chave na modelagem do processo erosivo. Assim sendo, objetivou-se avaliar a eficiência da cobertura vegetal, proporcionada pela cultura do milho, e suas relações com os atributos fitotécnicos desta cultura para alguns híbridos. O estudo foi realizado no campo demonstrativo de híbridos de milho da Universidade Federal de Lavras, localizada no município de Lavras, MG. Para determinação da cobertura vegetal utilizou-se um aparato que consiste em uma estrutura horizontal, contendo orifícios para visualização dos pontos com cobertura e sem cobertura vegetal, sendo as leituras feitas de forma aleatória e transversalmente às linhas da cultura. Os atributos fitotécnicos avaliados foram altura da planta, estande, matéria seca e produção de grãos. Diante dos resultados pode-se concluir que o maior índice de cobertura vegetal foi observado para os híbridos de milho P 30F33, P 30F90, P 3021, STRIKE, FORT, VALENT, UFLA 2001, UFLA 2004, CO 32, D 8480, D 8420 DKB 333B, DKB 440, evidenciando boa qualidade como planta protetora do solo. No período de maior ocorrência de chuvas, na região sul de Minas Gerais, a cultura do milho pode minimizar o efeito do processo erosivo. A produção de matéria seca relacionou-se bem com o índice de cobertura vegetal, podendo ser um indicativo quanto à proteção do solo.

The plant cover is a natural protection of soil against water erosion. In estimative models of soil loss, the effect of plant cover in the interception of rainfall kinetic energy is the key variable in the modeling of the erosive process. Thus, the aim of this work is to evaluate the efficiency of the plant cover provided by the corn crop and their relations with the phytotechnical attributes of this crop for its respective hybrids. This study was conducted in the corn hybrids demonstrative field at the Federal University of Lavras, Minas Gerais State, Brazil. In order to evaluate the plant cover a display was used that included a horizontal structure, containing holes for viewing the points with and without plant cover, the being readings performed at random and transversally to the crop lines. The phytotechnical attributes evaluated were plant height, stand, dry matter and grain production. It can be concluded that the higher plant cover index was observed for corn hybrids P 30F33, P 30F90, P 3021, STRIKE, FORT, VALENT, UFLA 2001, UFLA 2004, CO 32, D 8480, D 8420 DKB 333B, and DKB 440, proving good quality as a protective soil plant. In the period of larger occurrence of rainfall in the south of Minas Gerais state, the corn crop can minimize the effect of the erosive process. The production of dry matter was well correlated with the plant cover index, and can be used as evidence of soil protection.

Simulação de florestamento e da produção de milho através do modelo CERES: Maize / Mayze yeld and blooming date simulation by using CERES: Maize Model

A utilização dos computadores na agricultura tem trazido inúmeros benefícios ao empresário rural. Entre tais benefícios, a utilização de programas de computador para simular o crescimento e desenvolvimento de plantas; bem como o seu uso na otimização de práticas culturais, tem se mostrado como uma opção. Objetivou-se, neste trabalho, avaliar o programa CERES-Maize na simulação do florescimento e produção de milho (Zea mays L.), em diferentes cenários de investimento. Os resultados das simulações com o programa CERES-Maize mostraram que as diferenças entre as produções simuladas, comparadas com os dados obtidos em campo, estão entre os limites de 5% a 8% de erro, aceitáveis pelo programa. A mesma tendência foi verificada entre os valores observados e simulados para os dias de florescimento, em todos os cenarios. O programa CERES-Maize mostrou-se bastante robusto e eficiente nas simulações efetuadas. O uso desse programa pode ser visto como uma ferramenta adicional ao produtor no processo decisório, durante o planejamento da implantação da cultura.

The use of computers in agriculture has brought several benefits to the farmers. Among these benefits, the use of crop models to simulate plant growth and development, as well as a tool for optimization process and decision support aid, has been an option. The aim of this study was to evaluate the efficiency of Ceres-Maize model to simulate maize blooming date and yield at different investment scenarios. Simulation results showed that the difference between simulated and observed yield data were in the 5% and 8% error range, acceptable for the program. The same tendency was observed when comparing blooming dates in all scenarios. The model was very efficient and suitable for all of the simulations performed. Without any doubt CERES-Maize may be used as a tool, by farmers, in the crop planning process.

Spatial variability of soil acidity attributes and the spatialization of liming requirement for corn / Variabilidade espacial de atributos de acidez do solo e espacialização da necessidade de calagem para o milho

In Brazil, technicians, in most cases, ignore the aspects related to the spatial variability of the soil acidity attributes when liming requirement is calculated. The objective of this study was to validate the liming practice, evaluating the presence of spatial variability of the soil acidity attributes and the existence of areas with differentiated liming requirement, which were calculated by different methods. The experiment was carried out in an area cultivated with corn under conventional management and irrigation. The soil (0-0.2 m) was sampled in a conventional way (composite soil sample) and in a systematic scheme, by use of a grid sampling. In sequence to the soil fertility attributes analysis, it was calculated the liming requirement, according to the methods of SMP pH, aluminum neutralization and elevation of soil Ca and Mg levels, and increase of the soil base saturation. After the descriptive analysis of the data set was accomplished, the semivariograms were calculated and the maps were obtained through the kriging technique. Absence of spatial dependence, as well as the non necessity of limestone application, was observed for the Al neutralization calculation method. Spatial dependence was only verified for the soil acidity attributes and to the liming requirement calculated by the base saturation and SMP pH methods; for these two methods, the semivariogram ranges obtained varied from 35.7 to 200.5 m. The results have highlighted the existence of differentiated liming requirement zones when the variability of the soil acidity attributes was considered in the calculation of the dose and type of limestone to be used for corn soil acidity correction.

No Brasil, a prática de calagem desconsidera, na maioria das vezes, os aspectos relacionados à variabilidade espacial dos atributos de acidez do solo. Objetivou-se, neste estudo, validar a prática da calagem, avaliando a presença de variabilidade espacial de atributos de acidez do solo e a existência de áreas com necessidades diferenciadas de corretivo, por meio de diferentes métodos de cálculo da necessidade de calagem. O experimento foi realizado em lavoura de milho sob manejo convencional. O solo foi amostrado de forma convencional (amostra composta) e sistemática (mediante uso de grade amostral), na profundidade de 0-0,2 m. Posteriormente à análise de fertilidade de rotina, determinaram-se as necessidades de calagem segundo os métodos do tampão SMP, da neutralização de alumínio e elevação do Ca e Mg, e da saturação por bases. Após análise descritiva, foram obtidos os semivariogramas e os mapas por krigagem. Ausência de dependência espacial, assim como da necessidade de aplicação do corretivo calcário foram observadas para o método da neutralização de Al. A dependência espacial foi encontrada para os atributos de acidez do solo e para as necessidades de calagem calculadas pelos métodos de saturação por bases e pH SMP, com alcances variando entre 35,7 e 200,5 m. Esses últimos mostraram também, uma coincidência regionalizada entre as maiores demandas de calcário. Os resultados permitiram evidenciar a existência de zonas de aplicação de calcário diferenciadas, quando consideradas a variabilidade dos atributos de acidez do solo no cálculo espacializado da dose e o tipo de corretivo calcário a ser utilizado.

Desempenho de híbridos experimentais e comerciais de milho para produção de milho verde / Performance of experimental and commercial hybrids of maize for the production of green maize

Conduziu-se este trabalho com objetivo de avaliar o desempenho de 32 híbridos experimentais e 4 híbridos comerciais para produção de milho verde em Lavras, MG. O delineamento utilizado foi de blocos ao acaso com duas repetições. Foram avaliadas sete características de interesse agronômico e comercial para a produção de milho verde. Os dados obtidos foram submetidos à análise de variância, decompondo o efeito dos híbridos em híbridos comerciais, híbridos experimentais e híbridos comerciais versus híbridos experimentais. Foram feitos ainda estudos de correlação entre as diferentes características agronômicas dos híbridos. Entre os híbridos avaliados há híbridos experimentais promissores com desempenho superior a híbridos comerciais amplamente utilizados no Brasil. Considerando as características avaliadas, os híbridos AG 1051, AG 4051, GNS 03, GNS 21, GNS 23 e GNS 35 foram os mais promissores. É possível reduzir o número de características avaliadas em experimentos com milho verde, uma vez que existem associações entre as principais características avaliadas para essa finalidade. A produtividade de espigas empalhadas e despalhadas e a cor dos grãos são características imprescindíveis nessa avaliação.

The objective of this research was to evaluate the performance of thirty-two experimental hybrids and four commercial hybrids of green maize at Lavras, MG. The experimental design was a randomized blocks with two replications. Seven characteristics of agronomic and commercial interest for the production of green maize had been evaluated. For each experiment, the data obtained were submitted to the analysis of variance decomposing the effect of the hybrids in commercial hybrids versus experimental hybrids. There were still made studies of correlation among the different characteristics. Among all of evaluated hybrids, there are experimental promising hybrids with performance superior to the commercial hybrids widely utilized in Brazil. Taking into account all the characteristics evaluated, hybrids AG 1051, AG 4051, GNS 03, GNS 21, GNS 23 and GNS 35 were the most promising. It is possible to reduce the number of characteristics evaluated as green maize, since there are high associations among the main characteristics evaluated for this purpose. The yield of strawed ears along and the color of the grains are indispensable characteristics in that evaluation.