Genetic evaluation of grain sorghum hybrids in Brazilian environments using the REML/BLUP procedure

When it comes to recommending sorghum (Sorghum bicolor) cultivars, it is essential to carry out a genetic evaluation of the agronomic traits of promising genotypes from several common environments where the crop is cultivated. This study consisted of a genetic evaluation of 52 experimental grain sorghum hybrids and eight commercial cultivars. Hybrids were evaluated in 19 experiments representing the most varied cultivation conditions in Brazil. Traits of agronomic interest such as grain yield, flowering and plant height were analysed. Genotypic evaluation was performed following the REML/BLUP (Restricted Maximum Likelihood/Best Linear Unbiased Predictor) procedure; the MHPRVG (Harmonic Mean of Relative Performance of Genotypic Values) method was also employed to study stability and adaptability. Hybrids which stood out in terms of highest grain yield based on genotypic values, stability and adaptability were 0306037, 1G150, DKB 599, 0306039, 1G282 and 0307671. Of these, only 1G282 showed restrictions as to plant height. For flowering, experimental hybrids showed shorter cycles than commercial cultivars, confirming the efficiency of genetic improvement for this trait. With the analysis of grain yield considering days to flowering and plant height as covariates, it was observed that most of the hybrids of greater performance, showed grain yield to be positively influenced by plant height and days to flowering

Genotype x environment interaction via GGE Biplot/REML-BLUP in maize under nutritional stress

A seleção de genótipos para eficiência no uso (EU) é fundamental, pois permite alcançar produtividades satisfatórias, com menores custos e de modo sustentável. Assim, muitos programas de melhoramento para estresse nutricional fazem seleção de genótipos para dois ou mais estresses simultaneamente. No entanto é necessário entender o efeito do tipo e da intensidade do estresse nutricional para a composição da interação genótipo-ambiente (GxA). Neste contexto, uma ferramenta muito utilizada é a modelagem via GGE Biplot (efeitos principais dos genótipos (G) mais interação genótipo-ambiente (GA)) combinada com as equações de modelos mistos. Entretanto, é necessário entender como a predição e correção dos valores genéticos para os efeitos fixos interfere nas análises da interação GxA via GGE Biplot. Diante do exposto, o objetivo foi estudar o efeito do tipo e intensidade do estresse nutricional e do tratamento estatístico nos dados utilizados para compreensão da interação genótipo-ambiente em milho tropical. Para isto, foram avaliadas 41 combinações híbridas em dois experimentos, em baixa e alta disponibilidade de N e P, delineados em blocos ao acaso com duas repetições, em esquema fatorial simples (híbridos x níveis de N ou P). Os experimentos foram conduzidos em casa de vegetação (20o45'14"S; 42o52'53"W), na Universidade Federal de Viçosa, durante o mês de outubro de 2010. As plantas foram colhidas no estádio de seis folhas completamente expandidas (V6). Foram estimados a massa de parte aérea seca (MPS) e o comprimento de raiz lateral (CRLAT). Os dados obtidos foram submetidos a análises estatísticas via REML/BLUP (Máxima Verossimilhança Restrita/Melhor Preditor Linear Não Viesado) para a obtenção dos componentes de variância e as estimativas dos parâmetros genéticos e posteriormente submetido à análise via GGE Biplot. Foi possível concluir que a avaliação e seleção de genótipos de milho tropical deve ser realizada para cada nível de disponibilidade dentro de cada tipo de estresse nutricional e a utilização de médias fenotípicas apresenta maior confiabilidade em relação aos valores genotípicos nas análises da interação GxA via GGE Biplot.The selection of genotypes for use efficiency (UE) is essential because it allows achieving satisfactory yields with lower costs and sustainably. Thus, many nutritional stress breeding programs make a selection of genotypes for two or more stress simultaneously. However it is necessary to understand the effect of the type and intensity of nutritional stress for the composition of the genotype by environment interaction (GE). In this context, a commonly used tool is modeling via GGE biplot (genotype main effect (G) plus genotype by environment interaction (GE)) combined with mixed models. However, is necessary understand how the prediction and correction of breeding values for fixed effects change the analysis of GE interaction via GGE Biplot. Given the above, the objective was to study the effect of the type and intensity of nutritional stress and the statistical treatment given to the data used to understand the genotype-environment interaction in tropical maize. For this, 41 hybrids were evaluated in two experiments in high and low availability of N and P, using complete blocks design with two replications in a two-way scheme (hybrids x N or P levels). The experiments were conducted in a greenhouse (20o45'14"S; 42o52'53"W; 650 m), at the Federal University of Viçosa, during the month of October 2010. Plants were harvested at the V6 stage. The measured characters were dry shoot mass (MPS) and the length of lateral root (CRLAT). The data was subjected to statistical analysis via REML/BLUP (Restricted Maximum Likelihood/Best Linear Unbiased Predictor) for obtaining the variance components and estimation of genetic parameter and after subjected to analysis via GGE Biplot. Thus, we conclude that evaluation and selection of tropical maize genotypes should be performed for each level of availability within each type of nutritional stress and the use of phenotypic means has better reliability compared to the genotypic values in the analysis of GE interaction via GGE Biplot.Conselho Nacional de Desenvolvimento Científico e Tecnológic

Population structure analysis and identification of genomic regions under selection associated with low-nitrogen tolerance in tropical maize lines.

Increasing low nitrogen (N) tolerance in maize is an important goal for food security and agricultural sustainability. In order to analyze the population structure of tropical maize lines and identify genomic regions associated with low-N tolerance, a set of 64 inbred lines were evaluated under low-N and optimal-N conditions. The low-N Agronomic Efficiency index (LNAE) of each line was calculated. The maize lines were genotyped using 417,112 SNPs markers. The grouping based on the LNAE values classified the lines into two phenotypic groups, the first comprised by genotypes with high LNAE (named H_LNAE group), while the second one comprised genotypes with low LNAE (named L_LNAE group). The H_LNAE and L_LNAE groups had LNAE mean values of 3,304 and 1,644, respectively. The population structure analysis revealed a weak relationship between genetic and phenotypic diversity. Pairs of lines were identified, having at the same time high LNAE and high genetic distance from each other. A set of 29 SNPs markers exhibited a significant difference in allelic frequencies (Fst > 0.2) between H_LNAE and L_LNAE groups. The Pearson's correlation between LNAE and the favorable alleles in this set of SNPs was 0.69. These SNPs could be useful for marker-assisted selection for low-N tolerance in maize breeding programs. The results of this study could help maize breeders identify accessions to be used in the development of low-N tolerant cultivars

Early indirect selection for nitrogen use efficiency in maize1

Several studies to evaluate nitrogen use efficiency (NUE) have been carried out using early growth stages. However, there are no scientific reports on the ideal stage for evaluation and on which characteristics have the highest correlation with the NUE at that stage. The aim therefore was to identify the phenological stages and secondary characteristics which maximize accuracy in early indirect selection for NUE in maize. To do this, three endogamic maize strains were evaluated in a completely randomised design with five replications, in a triple factorial scheme (strains x N levels x phenological stage), at two contrasting nitrogen levels: low and high nitrogen. The plants were evaluated at five growth stages: stage nine (V9), with 14 fully-developed leaves (V14), tasseling (VT), flowering (R1) and physiological maturity (R6). The following characteristics were evaluated: efficiency in the usage, absorption, use and translocation of nitrogen; activity of nitrate reductase and glutamine synthetase; length of the lateral and axial roots; specific root area; chlorophyll content; number of leaves; plant height; stem diameter; and the levels of phosphorus and potassium. Considering the estimated direct and indirect gains, it can be concluded that the activities of glutamine synthetase at the V9 and V14 stages permit early indirect selection for nitrogen use efficiency in maize under conditions of low and high N availability respectively

Index selection of tropical maize genotypes for nitrogen use efficiency

Nitrogen (N) limitation in maize crops is related to the fact that the efficiency of nitrogen fertilization in maize does not exceed 50%, primarily due to volatilization, denitrification and soil leaching. Therefore, the development of new nitrogen use efficient (NUE) cultivars is necessary. The aim of the present study was to develop indices for the accurate selection of NUE maize genotypes for use in conditions of both high and low N availability. The experiment was conducted in a greenhouse (20º45'14"S; 42º52'53"W) at the Federal University of Viçosa during October 2010. A total of 39 experimental hybrid combinations and 14 maize lines differing in NUE were evaluated under two N availability conditions. We determined the relative importance of the studied characters using principal component analysis, factor analysis and by developing efficient selection indices. We conclude that indirect and early selection of tropical maize genotypes can be performed using the indices I HN = 0.022 SDM + 0.35 RSDM + 0.35 RL A + 0.35 NUE for high N availability environments and I LN = -0.06 RSDM + 0.35 RSA A + 0.35 RL A + 0.39 SDM for low N availability environments

Genetic Vulnerability and the Relationship of Commercial Germplasms of Maize in Brazil with the Nested Association Mapping Parents.

A few breeding companies dominate the maize (Zea mays L.) hybrid market in Brazil: Monsanto® (35%), DuPont Pioneer® (30%), Dow Agrosciences® (15%), Syngenta® (10%) and Helix Sementes (4%). Therefore, it is important to monitor the genetic diversity in commercial germplasms as breeding practices, registration and marketing of new cultivars can lead to a significant reduction of the genetic diversity. Reduced genetic variation may lead to crop vulnerabilities, food insecurity and limited genetic gains following selection. The aim of this study was to evaluate the genetic vulnerability risk by examining the relationship between the commercial Brazilian maize germplasms and the Nested Association Mapping (NAM) Parents. For this purpose, we used the commercial hybrids with the largest market share in Brazil and the NAM parents. The hybrids were genotyped for 768 single nucleotide polymorphisms (SNPs), using the Illumina Goldengate® platform. The NAM parent genomic data, comprising 1,536 SNPs for each line, were obtained from the Panzea data bank. The population structure, genetic diversity and the correlation between allele frequencies were analyzed. Based on the estimated effective population size and genetic variability, it was found that there is a low risk of genetic vulnerability in the commercial Brazilian maize germplasms. However, the genetic diversity is lower than those found in the NAM parents. Furthermore, the Brazilian germplasms presented no close relations with most NAM parents, except B73. This indicates that B73, or its heterotic group (Iowa Stiff Stalk Synthetic), contributed to the development of the commercial Brazilian germplasms

Accuracy and simultaneous selection gains for N-stress tolerance and N-use efficiency in maize tropical lines

Maize plants can be N-use efficient or N-stress tolerant. The first have high yields in favorable environments but is drastically affected under stress conditions; whereas the second show satisfactory yields in stressful environments but only moderate ones under optimal conditions. In this context, our aim was to assess the possibility of selecting tropical maize lines that are simultaneously N-stress tolerant and N-use efficient and check for differences between simultaneous selection statistical methods. Sixty-four tropical maize lines were evaluated for Nitrogen Agronomic Efficiency (NAE) and Low Nitrogen Tolerance (LNTI) response indices and two per se selection indices, Low Nitrogen Agronomic Efficiency (LNAE) and Harmonic Mean of Relative Performance (HMRP). We performed eight selection scenarios: LNAE; HMRP; Additive index; Mulamba-Mock index; and Independent culling levels. The last three was predicted by REML/BLUP single-trait and multi-trait using genotypic values of NAE and LNTI. The REML/BLUP multi-trait analysis was superior to the single-trait analysis due to high unfavorable correlation between NAE and LNTI. However, the accuracy and genotypic determination coefficient of NAE and LNTI were too low. Thus, neither single- nor multi-trait analysis achieved a good result for simultaneous selection nor N-use efficiency nor N-stress tolerance. LNAE obtained satisfactorily accurate values and genotypic determination coefficient, but its performance in selection gain was worse than HMRP, particularly in terms of N-use efficiency. Therefore, because of the superior performance in accuracy, genotypic determination coefficient and selection, HMRP was considered the best simultaneous selection methodology of the scenarios tested for N-use efficiency and N-stress tolerance

Accuracy and simultaneous selection gains for N-stress tolerance and N-use efficiency in maize tropical lines

ABSTRACT Maize plants can be N-use efficient or N-stress tolerant. The first have high yields in favorable environments but is drastically affected under stress conditions; whereas the second show satisfactory yields in stressful environments but only moderate ones under optimal conditions. In this context, our aim was to assess the possibility of selecting tropical maize lines that are simultaneously N-stress tolerant and N-use efficient and check for differences between simultaneous selection statistical methods. Sixty-four tropical maize lines were evaluated for Nitrogen Agronomic Efficiency (NAE) and Low Nitrogen Tolerance (LNTI) response indices and two per se selection indices, Low Nitrogen Agronomic Efficiency (LNAE) and Harmonic Mean of Relative Performance (HMRP). We performed eight selection scenarios: LNAE; HMRP; Additive index; Mulamba-Mock index; and Independent culling levels. The last three was predicted by REML/BLUP single-trait and multi-trait using genotypic values of NAE and LNTI. The REML/BLUP multi-trait analysis was superior to the single-trait analysis due to high unfavorable correlation between NAE and LNTI. However, the accuracy and genotypic determination coefficient of NAE and LNTI were too low. Thus, neither single- nor multi-trait analysis achieved a good result for simultaneous selection nor N-use efficiency nor N-stress tolerance. LNAE obtained satisfactorily accurate values and genotypic determination coefficient, but its performance in selection gain was worse than HMRP, particularly in terms of N-use efficiency. Therefore, because of the superior performance in accuracy, genotypic determination coefficient and selection, HMRP was considered the best simultaneous selection methodology of the scenarios tested for N-use efficiency and N-stress tolerance

Effect of F1 and F2 generations on genetic variability and working steps of doubled haploid production in maize.

For doubled haploid (DH) production in maize, F1 generation has been the most frequently used for haploid induction due to facility in the process. However, using F2 generation would be a good alternative to increase genetic variability owing to the additional recombination in meiosis. Our goals were to compare the effect of F1 and F2 generations on DH production in tropical germplasm, evaluating the R1-navajo expression in seeds, the working steps of the methodology, and the genetic variability of the DH lines obtained. Sources germplasm in F1 and F2 generations were crossed with the tropicalized haploid inducer LI-ESALQ. After harvest, for both induction crosses were calculated the haploid induction rate (HIR), diploid seed rate (DSR), and inhibition seed rate (ISR) using the total number of seeds obtained. In order to study the effectiveness of the DH working steps in each generation, the percentage per se and the relative percentage were verified. In addition, SNP markers were obtained for genetic variability studies. Results showed that the values for HIR, ISR, and DSR were 1.23%, 23.48%, and 75.21% for F1 and 1.78%, 15.82%, and 82.38% for F2, respectively. The effectiveness of the DH working step showed the same percentage per se value (0.4%) for F1 and F2, while the relative percentage was 27.2% for F1 and 22.4% for F2. Estimates of population parameters in DH lines from F1 were higher than F2. Furthermore, population structure and kinship analyses showed that one additional generation was not sufficient to create new genotype subgroups. Additionally, the relative efficiency of the response to selection in the F1 was 31.88% higher than F2 due to the number of cycles that are used to obtain the DH. Our results showed that in tropical maize, the use of F1 generation is recommended due to a superior balance between time and genetic variability