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Genomic selection has been implemented in several plant and animal breeding programs and it has proven to improve efficiency and maximize genetic gains. Phenotypic data of grain yield was measured in 147 maize (Zea mays L.) singlecross hybrids at 12 environments. Single-cross hybrids genotypes were inferred based on their parents (inbred lines) via single nucleotide polymorphism (SNP) markers obtained from genotyping-by-sequencing (GBS). Factor analytic multiplicative genomic best linear unbiased prediction (GBLUP) models, in the framework of multienvironment trials, were used to predict grain yield performance of unobserved tropical maize single-cross hybrids. Predictions were performed for two situations: untested hybrids (CV1), and hybrids evaluated in some environments but missing in others (CV2). Models that borrowed information across individuals through genomic relationships and within individuals across environments presented higher predictive accuracy than those models that ignored it. For these models, predictive accuracies were up to 0.4 until eight environments were considered as missing for the validation set, which represents 67% of missing data for a given hybrid. These results highlight the importance of including genotype-by-environment interactions and genomic relationship information for boosting predictions of tropical maize single-cross hybrids for grain yield. Made available in DSpace on 2020-12-22T09:02:13Z (GMT). No. of bitstreams: 1 Boosting-predictive.pdf: 1139997 bytes, checksum: 641636e15f14edc0b42f567b080ea4de (MD5) Previous issue date: 2020

Corn has experienced a true revolution in Brazil during the last 30 years (agricultural harvests from 1991/92 to 2021/2022). Currently, the country has established itself as the third producer and second exporter worldwide of this cereal, with a production of more than 100 million tons of this grain per agricultural year. In this period, soybean cultivation stands out as the great driver of technological advances, leading corn and other crops to more prominent positions and transforming grain production systems; previously monoculture or rotation, to more intensified systems, with two (or more) agricultural crops per year in the same area. The Brazilian Cerrado region, previously considered unsuitable for agriculture, is today the great barn of grain production in Brazil. In these three decades of escalation in corn production, some legal and technological milestones stand out, such as the Law for the Protection of Cultivars and its regulations (since 1997), the direct sowing system, the cultivation of corn in the second harvest (after soybean), and the use of biotechnologies. These factors were decisive for the growth of maize production to exceed by more than 3,6 times the volume of the 1991/92 agricultural season (30,7 million tons, at that time, to 112 million tons in 2021), while the area devoted to maize cultivation increased only 1,5 times (14 million ha in 1991/92 to 20,8 million ha after 30 years). Increases in productivity are linked to technologies and knowledge applied to the management of production systems, soybean-corn, and not only in an isolated crop; allowing greater advances in the gross production of both grains (recent yields in the corn harvest are about 2,5 times higher than 30 years ago ? reaching more than 5,3 t.ha-1). This article shows data and facts that allowed Brazil to get out of a position of vulnerability, in terms of corn supply, to become an important player in the production and marketing of this cereal worldwide. Made available in DSpace on 2022-05-25T05:05:11Z (GMT). No. of bitstreams: 1 Hitos-tecnologicos-que-cambiaron-el-rol-de-Brasil-en-la-produccion-de-maiz.pdf: 548589 bytes, checksum: 091e11cd4f9bc0d211542925a0de6fdc (MD5) Previous issue date: 2022

The objective of the present work was to evaluate the physiological quality in seeds of haploidy inducers of different types and origins. To this end, between December 2015 and March 2016, a series of physiological quality assessments were conducted on nine genotypes inducing haploidy in corn, namely: the gymnogenetic inducers Stock 6, TAIL P1 and TAIL P2; the hybrid between the TAIL P1 x TAIL P2 inductors; the hybrid TAIL P2 x TAIL P1, analogous to the previous hybrid, but with inversion of the female parent at the crossing; and androgenetic inducers W23, 90109 igig, 91202 igig and 91207 igig. The tests carried out were germination, accelerated aging, emergence in a bed, emergence index, fresh and dry mass, length of aerial part and root and the ratio between these characteristics, the humidity and the weight of 100 seeds. The results indicated that the physiological quality was improved throughout the selection for greater haploid induction. The haploidy induction system (andorgenetic or gymnogenetic) does not interfere with physiological quality, however the results obtained reinforce the need for care in the multiplication and conservation of haploidy inducing seeds in tropical conditions for their use in breeding. Made available in DSpace on 2022-02-22T18:01:01Z (GMT). No. of bitstreams: 1 Physiological-quality.pdf: 570877 bytes, checksum: c2c2779d3e58485e55420797f7a22058 (MD5) Previous issue date: 2021

The development of Al-tolerant cultivars is a complementary strategy to overcome the constraints caused by aluminum (Al) toxicity on acid soils and can contribute positively to the food supply for the growing global population. A major Al tolerance QTL in maize is controlled by a citrate transporter encoded by ZmMATE1. Our goal was to evaluate the impact of the superior allele of ZmMATE1 on the yield performance of maize lines and hybrids cultivated on acid soils. Near-isogenic lines carrying the superior allele of ZmMATE1 and the recurrent Al-sensitive parent were crossed with elite lines, generating near-isogenic hybrids contrasting for these alleles. All maize genotypes carrying this superior allele were more Al tolerant in nutrient solution than their isogenic counterparts having the ZmMATE1 allele derived from the Al-sensitive parent. These genotypes were cultivated in control and Al stress soils for two years. Al toxicity caused a significant yield reduction of 18.7% for lines and 14.7% for hybrids over the two years. The yield performance of maize genotypes declined in the second year compared with the first year, probably due to water deficiency after the grain-filling stage. The superior allele of ZmMATE1 in maize hybrids conferred yield gains from 21 to 48% compared with the hybrids harboring the alternative allele in the Al stress soil in the first and second years, respectively. As this superior allele is rare in maize and is likely absent in several elite germplasms, molecular breeding based on ZmMATE1 can improve maize yield stability on acid soils. Made available in DSpace on 2021-10-05T12:00:57Z (GMT). No. of bitstreams: 1 ZmMATE1-improves.pdf: 527806 bytes, checksum: 1c17744b02b4bc772fe3ed50786d1593 (MD5) Previous issue date: 2021

The objective of this work was to use the partial diallel methodology to compare double-haploid lines (DHs) of maize with lines obtained by traditional methods. To obtain hybrids, five double-haploid lines, used as female parents, were crossed with four testers, as male parents. Twenty hybrids were obtained from double-haploid lines, being: 8 experimental, and 8 commercial from Embrapa and 4 from other companies. Were evaluated; final stand (ST), tipping and breaking (LODG), plant height (PH), ear insertion height (EH), grain moisture at harvest (GM) and total grain weight (YIELD). Analysis of variance was performed, unfolding the degrees of freedom of the genotype, Tukey test at 5% probability, and the decomposition of the sums of squares of the treatments into general and specific combining ability for testers and DH lines. PH and EH were higher in hybrids derived from DHs lines, while productivity and final stand were higher in experimental controls. However, some hybrids, such as the hybrid DH1800007 presented higher YIELD than commercial and experimental controls. The data obtained demonstrate that hybrids derived from double-haploid lines, in addition to accelerating the time to obtain new cultivars, enable the development of hybrids with superior agronomic performance. Made available in DSpace on 2022-02-22T17:01:12Z (GMT). No. of bitstreams: 1 Agonomic-performance.pdf: 575272 bytes, checksum: 06cd61941c9447f6a9e82ea95098a9e7 (MD5) Previous issue date: 2021

Water deficit stress is the abiotic factor with the highest impact on crop yield. The objective of this study was to evaluate grain yield (GY), the anthesis-silking interval (ASI) and drought tolerance indices in maize hybrids. We evaluated GY and the ASI of 86 hybrids under two moisture levels (normal irrigation and water stress) for three consecutive years. The stress susceptibility index, water stress tolerance, drought resistance coefficient, drought resistance index, stress tolerance index and harmonic mean were evaluated. There were significant hybrid x environment interactions for GY and the ASI. Differences in the ASI among environments ranged from 0 to 5 days. The hybrids P3862, 1I873, 1I923, 1I862 and 1J1211 showed high GY, associated with the highest drought tolerance indices. The stress tolerance index and harmonic mean indices can be used to identify higher-yielding maize hybrids in environments with and without water restriction Made available in DSpace on 2020-04-15T01:01:16Z (GMT). No. of bitstreams: 1 Grainyield.pdf: 1830209 bytes, checksum: bb94f3b3d9bf3093fc7fd3bfc31b94af (MD5) Previous issue date: 2020

Genotyping-by-sequencing (GBS) datasets typically feature high rates of missingness and heterozygote undercalling, prompting the use of data imputation. We compared the accuracy of four imputation methods?NPUTE, Beagle, knearest neighbors imputation (KNNI), and fast inbreed line library imputation (FILLIN)?using GBS data of maize (Zea mays L.) inbred lines, genotyped using different multiplexing levels. Two strategies for SNP-calling and genotype imputation were evaluated. First, only lines genotyped through 96-plex were used for single nucleotide polymorphism (SNP) discovery, whereas both 96- and 384-plex were simultaneously used in the second strategy. In the first genotype imputation strategy, only the 96-plex lines were imputed, then the remaining lines were appended (96-plex-imputed plus 384-plex) and then imputed. In the second imputation strategy, we jointly imputed both datasets. We also investigated the impacts of including heterozygous genotypes and distinct rates of missing genotypes per locus. The different SNP-calling strategies and percentage of missing data did not substantially affect the imputation accuracy. However, the different imputation strategies showed a substantial effect. Generally, imputations were less accurate for heterozygotes. The scenario 96-plex-imputed plus 384-plex showed accuracies similar to the 96-plex scenario. Beagle and NPUTE produced the highest accuracies. Our results indicate that combining SNP-calling and imputation strategies can enhance genotyping in a cost-effective manner, resulting in higher imputation accuracies. Made available in DSpace on 2020-11-12T14:20:26Z (GMT). No. of bitstreams: 1 Single-nucleotide-polymorphism.pdf: 853268 bytes, checksum: 8621c2cd9ee8ae5d40282ce704ca311d (MD5) Previous issue date: 2020

The objective of this work was to evaluate commercial maize hybrids, under conventional sprinkler irrigation, in two sowing seasons (July and August 2017), in the municipality of Teresina, Piauí. Made available in DSpace on 2021-03-11T18:01:14Z (GMT). No. of bitstreams: 1 IrrigatedMaizeCropRBMS2020.pdf: 1040089 bytes, checksum: 3e55f2390d3eed00b1943662a3233bb5 (MD5) Previous issue date: 2020 Autoria na publicação: Lauro Moreira Guimarães, Paulo Evaristo Guimarães.

The objective of this study was to estimate the direct and indirect effects of agricultural, morphological, physiological, and root traits of popcorn lines, under two conditions of water supply: full irrigation (FI) and drought stress (DS). A complete randomized block design with three replications was used to evaluate the following traits: expanded popcorn volume per hectare (EPV), 100-grain weight (100GW), mean ear length, mean ear diameter, number of grains per row (NGR), prolificacy (PRO), anthesis to silking interval, tassel length, number of tassel branches, plant height, shoot dry matter, green index (SPAD), and canopy temperature depression (CTD), root angle (RA), tap root volume (TRV), and crown root volume (CRV). Analyses of variance and path analysis, and subsequent partitioning of direct and indirect effects were performed. For the traits EPV, PRO, CTD, RA, CRV and TRV, the genotype x environment interaction was significant. Drought stress had significant effects on EPV (&minus, 7.15%), 100GW (&minus, 23.52%), SPAD (&minus, 29.31%), CTD (87.15%), RA (24.54%), and CRV (44.89%). The traits NGR and SPAD were found to be decisive for the expression of EPV. The exploitation of these traits by indirect selection is expected to induce increments in EPV in environments under DS and FI.

To define breeding strategies, the understanding of trait inheritance is critical. The objective of this study was to determine the inheritance of popcorn under different water regimes. To this end, Hayman's diallel methodology was used, with 8 parents and 28 hybrids. The experiment was carried out under well-watered conditions (WW) and water stress (WS). For popping expansion (PE) under both water regimes, the effects of complete dominance and greater importance of the components associated with the dominance effects were observed. In contrast, the number of dominant genes was zero and the determination coefficient in the narrow sense was &gt, 50%, additive effects were also present. For the number of grains per row (GR), ear length (EL), and grain yield (GY) under WS and WW conditions, the dominance effects were the most relevant, and the mean degree of dominance with overdominance effects and greatest relevance of the components associated with this effect were also observed. The same breeding methods can be applied under the studied WS and WW conditions. Exploiting heterosis for GY and related components is a promising way to adapt popcorn to WS. To be able to capitalize on additive and dominance effects, a reciprocal recurrent selection is recommended.

Weighted outperformed unweighted genomic prediction using an unbalanced dataset representative of a commercial breeding program. Moreover, the use of the two cycles preceding predictions as training set achieved optimal prediction ability. Predicting the performance of untested single-cross hybrids through genomic prediction (GP) is highly desirable to increase genetic gain. Here, we evaluate the predictive ability (PA) of novel genomic strategies to predict single-cross maize hybrids using an unbalanced historical dataset of a tropical breeding program. Field data comprised 949 single-cross hybrids evaluated from 2006 to 2013, representing eight breeding cycles. Hybrid genotypes were inferred based on their parents’ genotypes (inbred lines) using single-nucleotide polymorphism markers obtained via genotyping-by-sequencing. GP analyses were fitted using genomic best linear unbiased prediction via a stage-wise approach, considering two distinct cross-validation schemes. Results highlight the importance of taking into account the uncertainty regarding the adjusted means at each step of a stage-wise analysis, due to the highly unbalanced data structure and the expected heterogeneity of variances across years and locations of a commercial breeding program. Further, an increase in the size of the training set was not always advantageous even in the same breeding program. The use of the two cycles preceding predictions achieved optimal PA of untested single-cross hybrids in a forward prediction scenario, which could be used to replace the first step of field screening. Finally, in addition to the practical and theoretical results applied to maize hybrid breeding programs, the stage-wise analysis performed in this study may be applied to any crop historical unbalanced data.

Resumo: O objetivo deste trabalho foi avaliar os efeitos genéticos aditivos e não aditivos sobre a eficiência de uso de P e a responsividade ao nutriente em linhagens de milho. Nove linhagens contrastantes - eficientes ou não quanto ao uso de P - foram avaliadas em cruzamentos dialélicos, em delineamento de blocos ao acaso, por dois anos, sob dois níveis de disponibilidade do nutriente em Latossolo Vermelho-Escuro distrófico. As linhagens L3 e L228-3 apresentaram os maiores efeitos médios da capacidade geral de combinação (CGC, ), o que é indício de eficiência, na ausência de P, e de responsividade, na presença. Os cruzamentos L51502020 x L22 e L36 x L56.800.84 apresentaram os maiores efeitos médios da capacidade específica de combinação (CEC, ), na presença e na ausência de P, respectivamente. Os componentes quadráticos para CGC foram superiores aos da CEC, na ausência de P, e inferiores, na presença, o que mostra que os efeitos aditivos predominaram na eficiência de uso, e os não aditivos, na responsividade ao nutriente. A capacidade combinatória dos genótipos interagiu com os ambientes; portanto, a seleção do melhor progenitor e da melhor combinação híbrida deve ser realizada para ambiente específico. As linhagens apresentam complementariedade gênica quanto à eficiência de uso de P. Abstract: The objective of this work was to evaluate additive and nonadditive genetic effects on responsiveness and the P use efficiency by maize lines. Nine contrasting inbred lines - efficient or not regarding their P use efficiency - were evaluated in diallel crosses, in a randomized complete block design, for two years, under two availability levels of the nutrient in an Oxisol. The lines L3 and L228-3 showed the highest average effects for general combining ability (GCA, ), indicating use efficiency in the absence of P, and responsiveness, in the presence. The crosses L51502020 x L22 and L36 x L56.800.84 had the highest average effects for specific combining ability (SCA, ) in the presence and in the absence of P, respectively. The quadratic components for GCA were higher than those of SCA, in the absence of P, and lower in the presence, showing that the additive effects predominated in P use efficiency, and the nonadditive ones predominated in the plant responsiveness to the nutrient. The genotype combining ability interacted with the environments; therefore, the selection of the best parent and of the best hybrid combination should be done in specific environments. The inbred lines show genic complementary action regarding P use efficiency.

Agricultural expansion and the need for sustainable cultivation are challenges faced by researchers involved in the generation of new cultivars that can adapt to abiotic stress. Knowledge of the genetic effects of characteristics related to efficiency and responsiveness to phosphorus use must be considered when implementing methods to obtain better genotypes. The aim of this study was to characterize and select popcorn hybrids based on their efficiency and responsiveness to phosphorus use, and estimate their combining abilities and genetic effects via diallel analysis to implement improvement programs for sustainable agriculture. Eight contrasting inbred lines were used to obtain simple hybrids for diallel analysis. Twenty-eight diallelic hybrids plus the popcorn parental lines were evaluated at two different sites under two contrasting environments for soil phosphorus availability (6×6 lattice design). Grain yield, popping expansion, and volume of expanded popcorn per hectare were measured. A combined analysis of variance and a test of means were performed. The classification and utilization of the phosphorus use efficiency index, according to the grain yield performance of the hybrids under contrasting environments, was considered. Through model 2 of the Griffing?s diallel analysis method, the general and specific combining abilities were estimated, along with their environmental interactions. The best strategy to obtain genotypes that are efficient and responsive to phosphorus involves exploring popcorn hybrids using genitors that result in the accumulation of additive genes that promote popping expansion. Hybrids P7×L80, P7×L59, P7×L76, and P6×L80 presented promising results and may be evaluated as cultivation options in phosphorus-deficient soils. Made available in DSpace on 2019-05-31T00:36:25Z (GMT). No. of bitstreams: 1 Geneticeffects.pdf: 753499 bytes, checksum: 7c7f95b7e2ade581ac6bb1b6acb4dc2d (MD5) Previous issue date: 2019

The objective of this study was to evaluate the effects of additive and non-additive genes on the efficiency of nitrogen (N) use and N responsiveness in inbred popcorn lines. The parents, hybrids and reciprocal crosses were evaluated in a 10x10 triple lattice design at two sites and two levels of N availability. To establish different N levels in the two experiments, fertilization was carried out at sowing, according to soil analysis reports. However, for the experiments with ideal nitrogen availability, N was sidedressed according to the crop requirement, whereas for the N-poor experiments sidedressing consisted of 30% of that applied in the N-rich environment. Two indices were evaluated, the Harmonic Mean of the Relative Performance (HMRP) and Agronomic Efficiency under Low Nitrogen Availability (AELN), both based on grain yield at both N levels. Both additive and non-additive gene effects were important for selection for N-use efficiency. Moreover, there was allelic complementarity between the lines and a reciprocal effect for N-use efficiency, indicating the importance of the choice of the parents used as male or female. The best hybrids were obtained from inbred popcorn lines with contrasting N-use efficiency and N responsiveness. Made available in DSpace on 2019-10-11T18:11:16Z (GMT). No. of bitstreams: 1 Relativeimportance.pdf: 871260 bytes, checksum: 6929b969c6d9ad09a4aed2bffa897c0f (MD5) Previous issue date: 2019

Knowing the inheritance of traits is essential to establish selection strategies in breeding programs. The aim of this study was to determine the genetic control of traits related to the phosphorus use efficiency in maize. A total of 280 progenies were developed according to design III, which were evaluated in the field under high and low phosphorus (P) availability. The genetic variance components were estimated for the agronomic traits and indices that define P use efficiency. The results indicated that the additive and dominance effects were important in explaining the genetic variability for the flowering time, grain yield and P efficiency indices. However, dominance effects prevailed, indicating that breeding efforts should be made to develop hybrids exploiting the heterosis for traits related to P use efficiency. Conhecer a herança de características utilizadas na seleção é fundamental para estabelecer estratégias de melhoramento. O objetivo desse trabalho foi determinar o controle genético de características relacionadas à eficiência no uso de fósforo em milho. Foram desenvolvidas 280 progênies segundo delineamento III, que foram avaliadas em ambientes com alta e baixa disponibilidade de fósforo (P). Os componentes de variância genética foram estimados para as características agronômicas e para os índices que compõem a eficiência de uso de P. Os efeitos aditivos e de dominância foram importantes para explicar a variabilidade genética para as características de florescimento, produtividade de grãos e para os índices de eficiência ao P. Contudo, houve predomínio dos efeitos de dominância, indicando que, do ponto de vista de melhoramento, esforços devem ser direcionados para obtenção de híbridos a fim de explorar a heterose para as características relacionadas à eficiência no uso de P.

Marginal soil fertility, soil acidity, aluminum toxicity, and a generalized low level of available nutrients, especially phosphorus (P), are major limiting factors to maize production in highly weathered oxisols that are prominent in the tropics. Plants have evolved several strategies to improve P acquisition, including the ability to associate with soil microorganisms that potentially enhance P uptake and plant nutrition. We investigated the effect of two maize genotypes with contrasting P use efficiency and their hybrid, grown in soils with two P levels, on bacterial and fungal community structures in the root and the rhizosphere. We found that a significant fraction of bacterial and fungal diversity could be attributed to the host genotype, but in general, the soil P level was the major driver of microbiome structure followed by plant compartment (rhizosphere versus directly root associated). Slow-growing bacterial taxa increased in the low P soil, whereas fast-growing taxa were enriched in high P soil. The low P soil had a positive effect on arbuscular mycorrhizal fungi abundance, as expected, particularly inside the root. On the other hand, our results did not support selection for microbes associated to plant growth promoting and P solubilization based on P availability. Taken together, our results expand knowledge of which microbial groups are favored in P-deficient oxisol and suggest that P fertilization significantly impacts the species composition and diversity indices of bacteria and fungi communities, both inside the roots and in the rhizosphere. Made available in DSpace on 2018-11-15T00:26:52Z (GMT). No. of bitstreams: 1 Rootassociated.pdf: 1316925 bytes, checksum: b9f7c63b9767b7ed56973f61d7f4b8b8 (MD5) Previous issue date: 2018-11-14

RESUMO - O Banco Ativo de Germoplasma de Milho (BAGMilho) preservado na Embrapa Milho e Sorgo mantem cerca de 4.000 variedades. Entretanto, essas variedades nao tem o padrao agronomico das cultivares comerciais, o que reduz o seu potencial do uso direto. O pre-melhoramento possibilita o desenvolvimento de genotipos com maior poten-cial de uso por meio da hibridizacao entre acessos do BAGMilho e genotipos melhorados. O objetivo deste trabalho foi avaliar familias endogâmicas obtidas de cruzamentos entre linhagens-elite e os acessos do BAGMilho composto-fonte de resistencia a mancha-branca e composto-fonte de resistencia a ferrugem-polissora quanto a reacao a patogenos, produtividade e caracteres agronomicos. Familias endogâmicas derivadas de retrocruzamentos entre estes compostos-fonte de resistencia e linhagens-elite foram avaliadas em cruzamentos com testadores dos grupos heteroticos duro e dentado. Os ensaios foram conduzidos em Sete Lagoas e Nova Porteirinha em duas epocas de semeadura. Os resulta-dos permitiram selecionar as familias endogâmicas MB130, MB181, MB164, FP109, FP133, FP104, FP120, FP112, FP103 e FP140 para uso em cruzamentos com linhagens do grupo heterotico duro e as familias endogâmicas MB024, MB032, MB083, FP028, FP036 e FP020 para uso em cruzamentos com linhagens do grupo heterotico dentado. Palavras-chave: recursos geneticos, fitopatologia, Zea mays, Pantoea ananatis, Puccinia polysora. MAIZE PRE-BREDING FOR RESISTANCE TO WHITE SPOT AND POLYSORA RUST ABSTRACT - The Maize Active Germplasm Bank (GBMaize) preserves about 4,000 varieties of maize. However, these varieties do not have the standard commercial performance that reduces their potential of agricultural use. Pre -breeding enables the development of greater agricultural use of genotypes by hybridization between the accessions from GBMaize and improved genotypes. The aim of this study was to evaluate inbred families obtained from crosses between inbred lines and accessions of GBMaize called source of resistance to white spot composite and source of resistance to polysora rust composite in crosses for resistance to pathogens, grain yield and agronomic traits. Inbred families derived from crosses between inbred lines and source of resistance to white spot and source of resistance to polysora rust composites were evaluated in crosses with flint and dent heterotic patterns testers. The trials were conduc-ted in Sete Lagoas and Nova Porteirinha in two sowing dates for the evaluation of resistance to pathogens, yield and traits of agronomic importance. The results allowed select inbred families MB130, MB181, MB164, FP109, FP133, FP104, FP120, FP112, FP103 and FP140 for use in crosses with flint heterotic pattern and inbred families MB024, MB032, MB083, FP028, FP036 and FP020 for use in crosses with dent heterotic pattern. Keywords: renetic resources, phytopathology, Zea mays, Pantoea ananatis, Puccinia polysora.

The expansion of agriculture, coupled with the need for sustainable cropping, is one of the greatest challenges of the scientific community working on the generation of new cultivars adapted to abiotic stress conditions. The aim of this study was to evaluate the variability of popcorn lines as to responsiveness and efficiency in phosphorus use, as a first step towards the implementation of a breeding program interested in the practice of sustainable agriculture. Twenty-five popcorn lines were evaluated in two locations with different phosphorus levels in the soil, using a randomized block design. The following traits were measured: plant height, ear height, female flowering date, male flowering date, male-female flowering interval, ear diameter, ear length, 100-grain weight, grain yield, popping expansion, and expanded popcorn volume per hectare. A combined analysis of variance and test of means were performed, and the lines were classified as to their phosphorus use efficiency, according to their production performance in the different environments. The genetic diversity between the lines was estimated by Tocher?s and UPGMA clustering methods, using generalized Mahalanobis distance. Lines L59, P7, P2, P3, P4, P8, P10, P9, L66, L70, L69, and P5 were efficient and responsive, whereas lines L75, L80, L61, L77, L63, L65, P1, L54, L53, L88, and L71 were inefficient and nonresponsive. Genetic variability was greater in the environments with low phosphorus in the soil, suggesting that the selection pressure exerted in the stressing environment is a decisive factor to obtain a higher expression of variability. Made available in DSpace on 2017-11-16T23:28:44Z (GMT). No. of bitstreams: 1 Intraspecificvariability.pdf: 615251 bytes, checksum: bcd3887c8cd3ea9aed0a31941e8b1f82 (MD5) Previous issue date: 2017-11-16

Tem sido observada, em milho, a redução da absorção de nitrogênio (N), por causa da deficiência de fósforo (P), mas o efeito dessa combinação na seleção de genitores ainda precisa de estudos. Os objetivos deste trabalho foram avaliar os efeitos das inter-relações de P e N na capacidade de combinação e seleção de genitores de milho. As 28 combinações híbridas (CH), obtidas de um dialelo completo entre oito genótipos de milho e três testemunhas, foram avaliadas em quatro ambientes, obtidos pelas combinações de alta e baixa disponibilidade de P e N. Avaliaram-se o rendimento de grãos (RG) e as características secundárias: altura de plantas (AP) e espigas (AE), índice de colheita (IC), peso volumétrico (PV), prolificidade (PRL) e massa seca da parte aérea (MSPA). O efeito do estresse de N no RG foi similar em baixo e alto P. O genótipo P3041 apresentou alto RG em todos os ambientes. As correlações genéticas das características secundárias com o RG foram afetadas pelos ambientes. Em alto P, a capacidade geral de combinação (CGC) foi significativa para RG apenas em alto N. Em baixo P, a CGC apresentou significância em ambos os níveis de N. Os genótipos AG1051 e P3041 tiveram estimativas positivas de CGC em todos os ambientes. Conclui-se que, para o rendimento de grãos, a CGC somente não é importante em alto P e baixo N e a CEC não é importante em estresse de P ou N. Phosphorus (P) deficiency has been reported to reduce nitrogen uptake (N) in maize, but the effect of this combination for parent selection still needs further studies. The objective of this work was to evaluate the interrelationship between P and N in the combining ability and parent selection in maize. Twent-eight hybrid combinations (CH), obtained from a complete diallel among eight maize genotypes, and three controls were evaluated in four environments characterized by a combination of high and low P and N availability. Grain yield (GY) and the secondary traits plant height (PH), ear height (EH), harvest index (HI), volumetric weight (VW), prolificacy (PRL) and dry weight of aerial parts (DWAP) were evaluated. The effect of nitrogen stress on GY was similar in the conditions of low and high P. The genotype P3041 showed high GY in all environments. Genetic correlations among secondary traits with GY were affected by all environments. In high P, the general combining ability (GCA) for GY was significant only in high N. In low P, GCA of GY showed significance at both N levels. The genotypes AG1051 and P3041 had positives estimates of GCA for GY in all environments. It was conclude that for grain yield, the GCA alone is not important at high P and low N and the specific combing ability is not important at low N or P.

O objetivo deste trabalho foi discriminar linhagens endogâmicas de milho por meio da avaliação de características radiculares fornecidas pela análise de imagens digitais, em doses contrastantes de nitrogênio no solo. Foram avaliadas seis linhagens endogâmicas de milho pertencentes à Embrapa Milho e Sorgo, em vasos de cinco litros contendo Latossolo Vermelho, textura média, em dois níveis diferenciados de adubação nitrogenada (zero e 2 mmol.L-1), na forma de nitrato de amônio. O delineamento experimental utilizado foi o de blocos casualizados, em esquema fatorial, com três repetições. Foi realizada a avaliação de características de raiz e parte aérea das plantas colhidas aos 23 dias após a semeadura. Foram observadas interações significativas entre as linhagens e doses de nitrogênio para comprimento radicular, superfície radicular, comprimento de raízes muito finas, superfície de raízes muito finas e superfície de raízes grossas, volume de raízes muito finas, massa seca da parte aérea e massa seca total. A linhagem CMS 28-7.1 apresentou menor proporção do volume da raiz muito fina/volume radicular em relação às outras linhagens. Em baixa disponibilidade de nitrogênio, as características radiculares diferenciaram as linhagens de milho e o volume de raízes muito finas.

Adoption of resistant cultivars is the primary measure used to control anthracnose stalk rot. The goal of this study was to identify maize-resistant genotypes to anthracnose stalk rot, which are similar to the hybrid 2B710. Experiments were performed at Embrapa Maize and Sorghum experimental fields in Brazil. The first experimental trial evaluated 234 maize lines as well as two commercials hybrids, BRS1010 (susceptible) and 2B710 (resistant). Artificial inoculations were performed with a strain at the blister (R2) phase, and evaluation of disease severity was performed after 30 days. The second experimental trial evaluated 48 maize lines and hybrids, inoculated with two Colletotrichum graminicola strains. In the first trial, eight resistance groups were formed, and the last lines were more resistant, as was the hybrid 2B710, with values between 11.50% and 23.0% of severity. In the second trial, there was an interaction between the two factors, lines and isolates, and the lines often showed the same reaction features as those obtained in the first trial. However, the disease severity was higher for most lines, even when using other isolates. These lines with effective levels of resistance could be used in future studies of inheritance, in programs to develop hybrids, and to identify molecular markers associated with resistance to anthracnose stalk rot in maize. RESUMO: O uso de cultivares resistentes é a principal medida para o manejo da antracnose do colmo em milho. Neste trabalho, objetivou-se identificar linhagens com níveis de resistência à antracnose do colmo, similar ao híbrido 2B710, considerado resistente. Dois experimentos foram conduzidos na Embrapa Milho e Sorgo. No primeiro experimento, foram avaliados 234 linhagens e os híbridos BRS1010 (suscetível) e 2B710 (resistente). Foi realizada inoculação artificial com um isolado de C. graminicola , na fase de pré-pendoamento e, após 30 dias, foi realizada a avaliação da severidade da antracnose no colmo. O segundo experimento foi conduzido com 48 linhagens e os híbridos inoculados com dois isolados de C. graminicola . No primeiro experimento, os genótipos formaram oito grupos com base na severidade da doença e as linhagens do último grupo foram consideradas as mais resistentes, incluindo o híbrido 2B710, em que os genótipos apresentaram valores de severidade entre 11,50 a 23%. No segundo experimento, houve interação entre os fatores linhagens e isolados e, de modo geral, as linhagens apresentaram a mesma tendência de reação obtida no primeiro experimento, no entanto, a severidade da doença foi maior para a maioria das linhagens, mesmo quando utilizado o outro isolado. Com isso, foi possível realizar a seleção de linhagens com bons níveis de resistência, as quais podem ser utilizadas em programas de melhoramento, em estudos de herança, desenvolvimento de híbridos e identificação de marcadores moleculares, associados com resistência à antracnose do colmo.

800x600 RESUMO - A determinacao do potencial de rendimento de hibridos de milho em condicoes distintas de uso de tecnologia fornece subsidios para a melhoria do manejo da cultura. O objetivo deste trabalho foi avaliar o desempenho de hibridos de milho experimentais e comerciais em dois ambientes com distintos niveis de tecnologia em praticas de manejo agronomico, na regiao de Sete Lagoas, MG. Os dois ambientes diferenciaram-se em relacao ao manejo do solo com adubos verdes, niveis de adubacao mineral, uso de produtos para tratamento de sementes, adubacoes foliares e uso de pulverizacao com fungicidas. Foram comparados cinco hibridos experimentais e um comercial da Embrapa, alem de quatro hibridos comerciais da iniciativa privada. Em cada ambiente, utilizou-se o delineamento experimental de blocos casualizados, com quatro repeticoes. Foram avaliados os componentes de produtividade por meio de analise de variância conjunta, a fim se verificar a existencia de interacao entre hibridos e ambientes de investimento tecnologico. Observou-se um incremento medio ao redor de 2 t ha-1 em produtividade de graos quando os hibridos foram cultivados com alto investimento tecnologico. Os hibridos 1I 862, 1I 873, AG 8088 YH e P 30F53 YH foram os de melhor desempenho, tanto no ambiente de medio quanto de alto nivel tecnologico, com produtividades medias de 12,65 e 14,87 t ha-1, respectivamente. Normal 0 21 false false false PT-BR X-NONE X-NONE MicrosoftInternetExplorer4

This study aims to describe the single-cross, super sweet corn hybrid BRS Vivi, with above-average ear diameter, light-colored grains and competitiveness with other sweet corn cultivars. BRS Vivi is a contribution to the expansion of the range of available cultivars on the market and the genetic basis of sweet corn in Brazil.

The purpose of this study was to evaluate 165 hybrids derived from lines previously selected for aluminum (Al) tolerance. Nine check cultivars were used, eight commercial hybrids and one experimental hybrid. Hybrids were evaluated at three levels of Al saturation (0, 20 and 40% on average). The differences between the environments were significant. Environment with 0% Al saturation yielded 29.5% more than that with 40% Al saturation, showing the importance of genotype selection for acid soils. The best check cultivar was the hybrid DKB550. The hybrids AG1020 and AG1040 also performed well, where the latter was more tolerant but the former more responsive to environment improvement. The hybrid BRS304 was susceptible to high levels of Al saturation. The three commercial BRS hybrids (BRS310, BRS330 and BRS332) performed better than BRS304 at high Al saturation. The hybrid BRS330 was the best BRS hybrid to grow on a field with high Al saturation. The hybrid DKB559 performed well at high Al saturation but did not respond to environment improvement. The hybrids 727029, 727039, 729041, 729095, 729109, AG1040, and DKB550 were tolerant to higher levels of Al saturation and responsive to environment improvement, and showed good stability and adaptability at both low and high Al saturation.

The objective of this study was to evaluate four maize testers for identification of superior inbreed lines in testcross. The four testers evaluated are cultivars with narrow or wide genetic base (single-cross hybrids and open pollinated varieties) and two kernel types (flint or dent). SynD and SynF testers are open pollinated varieties with dent and flint kernels, respectively, and FSH and DSH testers are single-cross hybrids with flint and dent kernels, respectively. SynD tester showed the biggest genetic variance among the maize inbreed lines in crosses. The effects of general combining ability (GCA) for lines and specific combining ability (SCA) for lines x testers were significant, whereas GCA effects for testers were not significant. SynD and SynF testers identified the largest number of lines with higher GCA. The DSH and FSH testers showed suitable to identify lines with high SCA. It was concluded that SynD and SynF testers are adequate to identify inbreed lines with high GCA effects, and it?s possible to identify new lines with high heterotic potential in each one of the four testers. RESUMO: O objetivo deste estudo foi avaliar quatro testadores de milho quanto à capacidade de identificar linhagens superiores em testcross. Os quatro testadores avaliados são cultivares com base genética ampla (variedades de polinização aberta) e estreita (híbridos simples) e dois tipos de grãos (duro e dentado). Os testadores SynD e SynF são populações de milho de polinização aberta com grãos dentados e duros, respectivamente, e FSH e DSH são híbridos simples com grãos duros e dentados, respectivamente. O testador SynD possibilitou a maior expressão de variância genética entre os cruzamentos com as linhagens. A capacidade geral de combinação (CGC) das linhagens e a capacidade específica de combinação (CEC) entre linhagens e testadores foram significativas, enquanto que os efeitos de CGC dos testadores foram não significativos. Concluiu-se que os testadores SynD e SynF mostram-se adequados para identificar linhagens com maiores efeitos de GCA e é possível identificar novas linhagens com alto potencial heterótico com cada um dos quatro testadores utilizados.

The objective of this study was to evaluate the performance, adaptability and stability of corn cultivars simultaneously in unbalanced experiments, using the method of harmonic means of the relative performance of genetic values. The grain yield of 45 cultivars, including hybrids and varieties, was evaluated in 49 environments in two growing seasons. In the 2007/2008 growing season, 36 cultivars were evaluated and in 2008/2009 25 cultivars, of which 16 were used in both seasons. Statistical analyses were performed based on mixed models, considering genotpes as random and replications within environments as fixed factors. The experimental precision in the combined analyses was high (accuracy estimates > 92 %). Despite the existence of genotype x environment interac-tion, hybrids and varieties with high adaptability and stability were identified. Results showed that the method of harmonic means of the relative performance of genetic values is a suitable method for maize breeding programs.

O objetivo deste trabalho foi conhecer a adaptabilidade e a estabilidade de variedades e híbridos de milho, quando submetidos a diferentes condições ambientais do Meio-Norte brasileiro. Para isso, procedeu-se à avaliação de 22 híbridos, em uma rede experimental, e de 20 cultivares (variedades e híbridos) em outra rede, em diferentes ambientes, utilizando-se o delineamento experimental em blocos ao acaso, com três repetições. Os híbridos mostraram melhor adaptação que as variedades. Em ambas as redes detectaram-se diferenças entre os genótipos e os ambientes e comportamento inconsistente desses genótipos na média dos ambientes. As cultivares diferiram quanto a adaptabilidade nos ambientes desfavoráveis. Entre as cultivares de melhor adaptação (b0 > média geral), os híbridos PL 1335 e SHS 5050 e a variedade SHS 500 mostraram-se exigentes nas condições desfavoráveis (b1 > 1) e o híbrido SHS 5070 e a variedade AL 34 mostraram ser pouco exigentes nessas mesmas condições (b1 < 1). Os híbridos que mostraram adaptabilidade ampla (b0 > média geral e b1 = 1) tornam-se de importância para a agricultura da região, tais como: DKB 390, DAS 8480, DKB 455, BRS 1010, BRS 1030, dentre outros.

O objetivo desse trabalho foi caracterizar uma população de milho por meio da análise de parâmetros genéticos em baixa e alta disponibilidade de nitrogênio. Assim, foi realizado experimento em delineamento em blocos ao acaso, com 162 linhagens, em dois ambientes contrastantes quanto à disponibilidade de nitrogênio, em esquema fatorial com três repetições. A população apresentou variabilidade genética para produtividade de grãos em baixo nitrogênio, com redução na média de altura de espiga, teor de clorofila, número de espigas, peso de espiga e produtividade de grãos em relação ao ambientes sem estresse. Os coeficientes de correlação genética entre produtividade de grãos e as outras características variaram de acordo com as doses de nitrogênio aplicadas. O número de espigas apresentou alta correlação genética com produtividade de grãos sob estresse, além de maior herdabilidade comparada à obtida em alto nitrogênio, possibilitando assim seu uso na seleção indireta de linhagens produtivas de milho cultivadas sob estresse de nitrogênio. The aim of this study was to characterize a maize population through the genetic parameters in high and low nitrogen availability. Thus, the experiment was conducted in a randomized block design with 162 lines in two contrasting environments in nitrogen availability in a factorial design with three replications. The population showed genetic variability for grain yield in low nitrogen, reducing the ear height, chlorophyll content, the number of ears, ear weight and grain yield in relation to the environment without stress. The coefficient's genetic correlation between grain yield and other characteristics vary according to levels of nitrogen applied. The number of ears showed high genetic correlation with grain yield under stress and high heritability compared with obtained under a high nitrogen, thus enabling its use for indirect selection of yield lines of maize grown under nitrogen stress.

A Embrapa desenvolve há mais de 30 anos o programa de melhoramento de milho para região subtropical. O presente trabalho tem por objetivo avaliar os resultados do Ensaio Elite Sul conduzido na região subtropical do Brasil na última década. Foram realizadas análises individuais e a análise conjunta dos locais nos anos, para as características produtividade de grãos (kg ha–1), umidade de grãos na colheita (%), altura de planta (cm) e inserção da primeira espiga (cm) e observado o número de híbridos avaliados, número de híbridos experimentais, média dos híbridos comerciais, número de híbridos com produtividade acima da média dos híbridos comerciais, número de híbridos com produtividade abaixo da média dos híbridos comerciais. Nos últimos dez anos foram obtidos anualmente, em média, nove híbridos de elevada produtividade de grãos, onze mais precoces, 16 de menor estatura de planta e doze com inserção de espiga mais baixa, quando comparados com a média das testemunhas. Assim, pode-se afirmar que os esforços e os métodos empregados no programa de melhoramento de milho para região subtropical estão gerando produtos superiores. Nota técnica.

Publicado também na Agrosoft Brasil, 13 dez. 2010 e na Revista do Produtor Rural, ano 4, n. 22, p. 41-43, nov./dez. 2010.

The maize genebank (GBmaize) preserves nearly 4,000 accessions for conservation and use. The use is however restricted because the accessions do not performs as well as the elite genotypes. This problem can be reduced by pre-breeding, i. e., by extending the information on germplasm and introgressing useful alleles. Since irregular rainfall distribution and drought induce maize yield losses, drought tolerance is a man breeding target. In this study, the GBmaize accessions were evaluated for drought tolerance. Environmental factors, genotypes and the respective interactions influence the phenotypic expression. There was however no interaction genotype-irrigation level, so no accessions with different performance under the two water regimes could be identified. The performance of the following accessions was promising for a number of traits: SP154, BA166, MG099, CE002, SE025, BA154, BA194, BA085, MG076, PRO053, Roxo Macapá, SE016, and AL018. Made available in DSpace on 2011-04-09T19:02:26Z (GMT). No. of bitstreams: 1 Crop.pdf: 1497587 bytes, checksum: b055b532adde18165706de1d6ebb29c4 (MD5) Previous issue date: 2011-03-10

The objectives of this work were to caracterize the tropical maize germplasm and to compare the combining abilities of maize grain yield under different levels of environmental stress. A diallel was performed among tropical maize cultivars with wide adaptability, whose hybrid combinations were evaluated in two sowing dates, in two years. The significance of the environmental effect emphasized the environmental contrasts. Based on grain yield, the environments were classified as favorable (8,331 kg ha-1), low stress (6,637 kg ha-1), high stress (5,495 kg ha-1), and intense stress (2,443 kg ha-1). None of the genetic effects were significant in favorable and intense stress environments, indicating that there was low germplasm variability under these conditions. In low and high stresses, the specific combining ability effects (SCA) were significant, showing that the nonadditive genetic effects were the most important, and that it is possible to select parent pairs with breeding potential. SCA and grain yield showed significant correlations only between the closer environment pairs like favorable/low stress and high/intense stress. The genetic control of grain yield differed under contrasting stress environments for which maize cultivars with wide adaptability are not adequate. O objetivo deste trabalho foi caracterizar o germoplasma de milho e comparar a capacidade de combinação da produtividade do milho em ambientes com diferentes graus de estresse. Um dialelo foi realizado entre cultivares de milho tropical com ampla adaptabilidade, cujas combinações híbridas foram avaliadas em duas épocas de plantio, em dois anos. A significância do efeito ambiental mostrou que os ambientes foram contrastantes. Com base na produtividade, os ambientes foram classificados como: favorável (8.331 kg ha-1); com baixo estresse (6.637 kg ha-1); com alto estresse (5.495 kg ha-1); e com intenso estresse (2.443 kg ha-1). Nenhum dos efeitos genéticos foi significativo nos ambientes classificados como favorável e com intenso estresse, o que indica haver baixa variabilidade para as combinações genéticas nesses ambientes. Em baixo e alto estresse, os efeitos da capacidade de combinação específica foram significativos, o que mostra que os efeitos genéticos não aditivos foram os mais importantes, e que é possível selecionar pares de genitores com potencial para melhoramento. A capacidade geral de combinação e a produtividade de grãos apresentaram correlações significativas somente entre os ambientes mais próximos como favorável/baixo estresse e alto/intenso estresse. O controle genético da produtividade de grãos difere em ambientes contrastantes quanto ao estresse para os quais as cultivares de milho com ampla adaptabilidade não são adequadas.

The objectives of this work were to evaluate the genotype x environment (GxE) interaction for popcorn and to compare two multivariate analyses methods. Nine popcorn cultivars were sown on four dates one month apart during each of the agricultural years 1998/1999 and 1999/2000. The experiments were carried out using randomized block designs, with four replicates. The cv. Zélia contributed the least to the GxE interaction. The cv. Viçosa performed similarly to cv. Rosa-claro. Optimization of GxE was obtained for cv. CMS 42 for a favorable mega-environment, and for cv. CMS 43 for an unfavorable environment. Multivariate analysis supported the results from the method of Eberhart & Russell. The graphic analysis of the Additive Main effects and Multiplicative Interaction (AMMI) model was simple, allowing conclusions to be made about stability, genotypic performance, genetic divergence between cultivars, and the environments that optimize cultivar performance. The graphic analysis of the Genotype main effects and Genotype x Environment interaction (GGE) method added to AMMI information on environmental stratification, defining mega-environments and the cultivars that optimized performance in those mega-environments. Both methods are adequate to explain the genotype x environment interactions. Os objetivos deste trabalho foram avaliar a interação genótipo x ambiente (GxA) em milho-pipoca e comparar dois métodos de análise multivariada (AMMI e GGE). Os tratamentos foram nove cultivares de milho-pipoca, plantadas em quatro épocas de semeadura em cada ano de cultivo em 1998/1999 e 1999/2000. O delineamento foi em blocos ao acaso, com quatro repetições. A cultivar Zélia foi a que menos contribuiu para a interação GxA. As cultivares Viçosa e Rosa-claro mostraram desempenhos similares. A otimização da interação GxA foi obtida com a cv. CMS 42 para mega-ambientes favoráveis e com a cv. CMS 43 para ambientes desfavoráveis. Os resultados das análises multivariadas corroboraram os resultados do método de Eberhart & Russell. A análise gráfica do método Additive Main effects and Multiplicative Interaction (AMMI) é simples e permite tirar conclusões sobre estabilidade, desempenho genotípico, divergência genética das cultivares, e sobre os ambientes que otimizam o desempenho das cultivares. A análise gráfica do método Genotype main effects and Genotype x Environment interaction (GGE) acrescentou informações de estratificação ambiental ao AMMI e definiu mega-ambientes e as cultivares que tiveram suas performances otimizadas nesses ambientes. Ambos os métodos são adequados para explicar a interação genótipo x ambiente.

The objectives of this work were to study the genetic control of grain yield (GY) and nitrogen (N) use efficiency (NUE, grain yield/N applied) and its primary components, N uptake efficiency (NUpE, N uptake/N applied) and N utilization efficiency (NUtE, grain yield/N uptake), in maize grown in environments with high and low N availability. Experiments with 31 maize genotypes (28 hybrid crosses and three controls) were carried out in soils with high and low N rates, in the southeast of the state of Minas Gerais, Brazil. There was a reduction of 23.2% in average GY for maize grown in soil with low N, in comparison to that obtained with high N. There were 26.5, 199 and 400% increases in NUtE, NUpE, and NUE, respectively, for maize grown with low N. The general combining ability (GCA) and specific combining ability (SCA) were significant for GY, NUE and NUpE for maize grown in high N soil. Only GCA was significant for NUpE for maize grown in low N soil. The GCA and SCA for NUtE were not significant in either environment. Additive and non-additive genetic effects are responsible for the genetic control of NUE and GY for maize grown in soils with high N availability, although additive effects are more important. RESUMO: O objetivo deste trabalho foi estudar o controle genético da produtividade de grãos (PG) e da eficiência no uso de nitrogênio (EUN, produção de grãos/N aplicado) e seus componentes primários - eficiência de absorção (EAbN, N absorvido/N aplicado) e utilização (EUtN, produção de grãos/N absorvido) -, em milho cultivado em ambientes com alta e baixa disponibilidade de nitrogênio. Trinta e um genótipos de milho (28 cruzamentos entre híbridos comerciais e três testemunhas) foram avaliados em solos com alta e baixa doses de aplicação de N. Houve redução de 23,2% na média de PG em milho cultivado em solo com baixo teor de N, em relação à obtida com alto N. Com baixo teor de N no solo, observaram-se aumentos de 26,5, 199 e 400% em EUtN, EAbN, e EUN, respectivamente. Em milho cultivado em solo com alto teor de N, as capacidades geral (CGC) e específica (CEC) de combinação foram significativas em PG, EUN e EAbN. Em milho de solos com baixo teor de N, apenas a CGC, na EAbN, foi significativa. A CGC e a CEC não foram significativas, em nenhum dos ambientes, na EUtN. Efeitos genéticos aditivos e não aditivos são responsáveis pelo controle genético da EUN e PG, em milho cultivado em solos com elevada disponibilidade de N, mas os efeitos aditivos são mais importantes. Made available in DSpace on 2017-06-09T23:54:13Z (GMT). No. of bitstreams: 1 Geneticcontrol.pdf: 456191 bytes, checksum: 0bcb13a6bbeb77e1501a974f5e355773 (MD5) Previous issue date: 2009-01-12

The purpose of this study was to evaluate the nitrogen-use efficiency of 15 corn hybrids in different environments. The experiment was conducted at the research station Embrapa Milho e Sorgo, in environments with low (12 kg ha-1) and high (120 kg ha-1) nitrogen fertilization, in a randomized block design with three replications. The chlorophyll content, leaf nitrogen and nitrate reductase activity in the flag leaf were determined at flowering and the grain yield was evaluated at harvest. The chlorophyll content proved to be sensitive to nitrogen availability, although without discriminating genotypic differences efficiently. To use nitrate reductase for this purpose, further studies are needed on the reliability of this biochemical variable to diagnose genotypes efficient in N use precociously. The hybrid L2xL3 was considered promising for maize breeding programs aimed at gene introgression related to N-use efficiency.

O nitrogênio é um dos elementos mais exigidos pela cultura do milho, sendo o nutriente que mais onera a produção agrícola, pois em grande parte dos solos agricultáveis, este elemento não está disponível em quantidades necessárias para altas produtividades, exigindo aplicações suplementares. Além disso, os cultivares comerciais de milho são altamente dependentes de adubações nitrogenadas, pois foram desenvolvidos para cultivo em ambientes otimizados, não sendo adaptados a condições de baixa disponibilidade de N. Assim, os objetivos deste trabalho foram promover uma melhor caracterização de linhagens de milho desenvolvidas em solos com baixo nitrogênio, determinar os padrões de herança da eficiência de uso de N e da resposta à aplicação deste nutriente quanto às capacidades gerais e específicas de combinação e investigar o comportamento dos genótipos quanto à adaptabilidade e estabilidade em ambientes contrastantes na disponibilidade de nitrogênio. Os resultados demonstraram que linhagens eficientes tendem a produzir híbridos eficientes e responsivos, de adaptabilidade geral e com boa estabilidade. Os efeitos genéticos aditivos e não aditivos para produtividade de grãos forma importantes em ambientes com baixo ou alto N. Entretanto, o controle genético da produtividade foi diferente para ambientes contrastantes na disponibilidade de N e a tendência da importância dos efeitos aditivos, em relação aos efeitos de complementação gênica, variou entre os conjuntos de genótipos avaliados. A decomposição dos parâmetros de adaptabilidade de Eberhart e Russell (1966) em efeitos de CGC e CEC proporcionaram melhor entendimento da herança da adaptação a ambientes com baixo N, e da resposta dos cultivares à aplicação deste nutriente. O uso da estatística Pi (Lin Binns, 1988) permitiu a identificação de genótipos superiores quanto a eficiência e resposta ao N, e, ao mesmo tempo, de adaptabilidade ampla e boa estabilidade de produção. A população CMS 59 mostrou-se como a mais promissora para extração de linhagens eficientes no uso de N e com altas frequências de alelos favoráveis para produção de grãos em ambientes com baixo , entretanto, linhagens com altas estimativas de CGC e que apresentem boas capacidades específicas de combinação com linhagens da CMS 59 foram encontradas em todas as populações avaliadas. Desta forma, para desenvolvimento de cultivares eficientes no uso de N propõe-se a avaliação de genótipo em ambientes com baixo N, e, posteriormente, a obtenção de progênes híbridas apenas das linhagens mais adaptadas ao estresse por deficiência de N, em dialelos ou top-crosses, para avaliações mais detalhadas. Este esquema proporcionaria economia de recursos pela diminuição do número de progênies testadas. Made available in DSpace on 2019-03-14T00:25:53Z (GMT). No. of bitstreams: 1 TeseLauro.pdf: 556942 bytes, checksum: 2a4e3d0746de765e1af260e074cbf8e6 (MD5) Previous issue date: 2006 Tese (Doutorado em Genética e Melhoramento de Plantas) - Universidade Federal de Viçosa, Viçosa, MG.