João Cândido de Souza

Genotypic stability and adaptability in tropical maize based on AMMI and GGE biplot analysis.

We evaluated the phenotypic and genotypic stability and adaptability of hybrids using the additive main effect and multiplicative interaction (AMMI) and genotype x genotype-environment interaction (GGE) biplot models. Starting with 10 single-cross hybrids, a complete diallel was done, resulting in 45 double-cross hybrids that were appraised in 15 locations in Southeast, Center-West and Northeast Brazil. In most cases, when the effects were considered as random (only G effects or G and GE simultaneously) in AMMI and GGE analysis, the distances between predicted values and observed values were smaller than for AMMI and GGE biplot phenotypic means; the best linear unbiased predictors of G and GE generally showed more accurate predictions in AMMI and GGE analysis. We found the GGE biplot method to be superior to the AMMI 1 graph, due to more retention of GE and G + GE in the graph analysis. However, based on cross-validation results, the GGE biplot was less accurate than the AMMI 1 graph, inferring that the quantity of GE or G + GE retained in the graph analysis alone is not a good parameter for choice of stabilities and adaptabilities when comparing AMMI and GGE analyses.

Híbridos de milho inter e intrapopulacionais obtidosa partir de populações s0 de híbridossimples comerciais

O objetivo deste trabalho foi avaliar a viabilidade de se produzir hibridos inter e intrapopulacionais a partir de populacoes S0 de hibridos simples comerciais. Foram utilizadas tres populacoes S0 oriundas dos hibridos simples comerciais P30F45, Dow657 e DKB333B, sendo obtidos 163 hibridos (110 interpopulacionais e 53 intrapopulacionais). A avaliacao dos hibridos, em relacao a produtividade de graos, foi realizada no ano agricola 2003/2004, nos municipios de Lavras e Lambari (MG), em delineamento latice simples 13 x 13, utilizando-se como testemunhas os tres hibridos comerciais e suas populacoes S0. Os dados foram submetidos a analise de variância individual e conjunta. A partir das esperancas dos quadrados medios foram estimados alguns parâmetros geneticos e fenotipicos. A depressao por endogamia dos hibridos comerciais tambem foi estimada. Foram identificados hibridos S0 interpopulacionais superiores, tanto aos hibridos simples comerciais quanto a suas geracoes S0, em ambos os locais. Por outro lado, nao se identificou nenhum hibrido intrapopulacional superior a media dos hibridos comerciais, devido, em parte, ao numero de hibridos intrapopulacionais avaliados, 53 contra 110 hibridos S0 interpopulacionais. No entanto, foram identificados hibridos S0 intrapopulacionais com produtividade media de graos superior a 10 t ha-1. De acordo com os resultados e possivel obter hibridos, a partir de populacoes S0 de hibridos simples comerciais, com maior produtividade de graos. Verificou-se tambem, que hibridos simples comerciais sao excelente alternativa para a extracao de linhagens, ja que, em geracoes iniciais de endogamia, a obtencao de hibridos superiores ja e viavel.

Adaptability and stability of maize varieties using mixed model methodology

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 genotypes 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.

ALTERNATIVES FOR OBTAINING DOUBLE CROSS MAIZE HYBRIDS

Com o objetivo de verificar a multiplicacao, expressao de sintomas foliares e efeito dos molicutes na producao de diferentes genotipos de milho, fitoplasma e Spiroplasma kunkelii foram inoculados, isolada ou simultaneamente, em cinco cultivares, mantidas em vasos ate a producao. Plantas sadias de todas as cultivares foram utilizadas como controle. Em cada vaso, foram cultivadas duas plantas, sendo uma utilizada para a deteccao dos molicutes na ultima folha completamente expandida, aos 30, 60 e 100 dias apos a inoculacao. A outra planta foi utilizada para deteccao dos molicutes nas folhas inferiores, medianas e apicais, aos 100 dias apos a inoculacao. O percentual de reducao causado pelos molicutes na altura e na producao de graos foi determinado nas duas plantas, em relacao as plantas sadias. A expressao de sintomas foliares e os resultados positivos obtidos na deteccao dos molicutes foram mais evidentes aos 100 dias apos a inoculacao. O periodo de enchimento de graos foi considerado a fase mais adequada para a deteccao desses patogenos. Os molicutes foram detectados nas folhas inferiores, medianas e apicais, observando-se maior frequencia nas folhas apicais. Verificou-se predominância de infeccao por espiroplasma e maior efeito detrimental desse patogeno no crescimento e producao das plantas em relacao ao fitoplasma. Nao foi detectado efeito sinergistico significativo dos dois molicutes sobre o crescimento e producao das plantas. Observou-se que o efeito prejudicial desses patogenos sobre o crescimento e producao das cultivares foi determinado pela frequencia de plantas infectadas.Apesar do amplo uso de deltametrina para controlar pragas do milho, no Brasil, existem poucas informacoes sobre o seu impacto nos artropodes associados a cultura. Este trabalho teve como objetivo avaliar os efeitos da pulverizacao de deltametrina em atropodes pragas e predadores mais comuns na parte aerea do milho. O delineamento foi em blocos casualizados, com quatro repeticoes. No estadio de dez folhas expandidas, o inseticida (Decis 25 CE, 7,5 gi.a./ha) foi pulverizado no cartucho das plantas e amostragens realizadas em dez plantas/parcela (1 dia antes, 7, 10, 14, 21 e 28 dias apos a pulverizacao) determinaram a densidade populacional ou a ocorrencia dos artropodes e a percentagem de plantas atacadas por Spodoptera frugiperda . O inseticida controlou a infestacao de S. frugiperda ate sete dias apos a pulverizacao e, nesse periodo, tambem reduziu em 64% a densidade populacional da cigarrinha Dalbulus maidis nas parcelas tratadas. O inseticida nao afetou negativamente o complexo de artropodes predadores associados a parte aerea do milho, mostrando toxicidade seletiva em favor de ninfas e adultos de Doru luteipes , de um grupo nao identificado de formigas e de aranhas. Esses resultados sao favoraveis ao uso de deltametrina em programas de manejo de S. frugiperda na cultura do milho, principalmente nos agroecossistemas com elevada abundância de predadores.Com o objetivo de estudar o efeito da omissao de P no meio de cultura nas caracteristicas fisiologicas de absorcao de P e no comprimento de raizes de oito genotipos de milho, quatro previamente classificados como eficientes e quatro como ineficientes para P, foram desenvolvidos dois experimentos. No primeiro, sementes dos oito hibridos de milho foram germinadas em rolos de papel-toalha e transplantadas para recipientes de plastico contendo solucao nutritiva completa de Steinberg, pH 5,5. Sete dias apos o transplante, o P foi retirado de metade das bandejas. Apos tres dias de omissao de P, realizou-se a cinetica de absorcao de P, iniciando-se a retirada de aliquotas de 10 ml de cada vaso, a cada 30 minutos, durante oito horas. No segundo experimento, aos seis dias apos a omissao do P no meio de cultivo, raizes das plantas dos tratamentos com e sem omissao de fosforo foram coletadas para avaliacao do comprimento total do sistema radicular. A omissao de fosforo por tres dias aumentou significativamente a velocidade maxima de absorcao de fosforo (Vmax) e a taxa de influxo em seis genotipos de milho, quatro ineficientes e dois eficientes para P. O Km (Constante de Michaelis) foi significativamente modificado pela omissao de fosforo em apenas dois genotipos. Conclui-se que aumentos na Vmax e taxa de influxo de P com a omissao de P no meio de cultivo e um mecanismo geral de resposta das plantas a deficiencia de P, mas que nao confere eficiencia diferencial entre genotipos de milho. A omissao de P na solucao nutritiva, por seis dias, aumentou significativamente o comprimento radicular em tres dos genotipos eficientes para P. Nos genotipos ineficientes para P, nao houve modificacao significativa dessas caracteristicas, indicando que o crescimento diferencial do sistema radicular pode ser um dos possiveis mecanismos da eficiencia para fosforo em milho.

Stability of combining ability effects in maize hybrids

General and specific combining ability effects are important indicators in a maize (Zea mays L.) breeding program aiming hybrid development. The objectives of the present study were to estimate the general (GCA) and specific combining abilities (SCA) effects of commercial maize hybrids using a complete diallel scheme and to assess the stabilities of these estimates. Fifty-five entries were assessed; ten commercial single-crosses and all possible double-crosses. The experiments were carried out in 12 environments in the 2005/06 growing season. A randomized complete block design was used with three replications per environment. Ear yield was evaluated, corrected to 13% of moisture content. The combined diallel analysis involving all environments was performed and the stability of general and specific combining ability effects was investigated. The underlying nonparametric statistics evaluated the contribution of each effect to the genotype by environment interaction. Non-additive effects were more important for this set of hybrids than the additive effects. It was possible to select parents with high stability for combining ability and with high GCA.

Genetic Architecture of Ear Fasciation in Maize (Zea mays) under QTL Scrutiny.

Maize ear fasciation Knowledge of the genes affecting maize ear inflorescence may lead to better grain yield modeling. Maize ear fasciation, defined as abnormal flattened ears with high kernel row number, is a quantitative trait widely present in Portuguese maize landraces. Material and Methods Using a segregating population derived from an ear fasciation contrasting cross (consisting of 149 F2:3 families) we established a two location field trial using a complete randomized block design. Correlations and heritabilities for several ear fasciation-related traits and yield were determined. Quantitative Trait Loci (QTL) involved in the inheritance of those traits were identified and candidate genes for these QTL proposed. Results and Discussion Ear fasciation broad-sense heritability was 0.73. Highly significant correlations were found between ear fasciation and some ear and cob diameters and row number traits. For the 23 yield and ear fasciation-related traits, 65 QTL were identified, out of which 11 were detected in both environments, while for the three principal components, five to six QTL were detected per environment. Detected QTL were distributed across 17 genomic regions and explained individually, 8.7% to 22.4% of the individual traits or principal components phenotypic variance. Several candidate genes for these QTL regions were proposed, such as bearded-ear1, branched silkless1, compact plant1, ramosa2, ramosa3, tasselseed4 and terminal ear1. However, many QTL mapped to regions without known candidate genes, indicating potential chromosomal regions not yet targeted for maize ear traits selection. Conclusions Portuguese maize germplasm represents a valuable source of genes or allelic variants for yield improvement and elucidation of the genetic basis of ear fasciation traits. Future studies should focus on fine mapping of the identified genomic regions with the aim of map-based cloning.

Early selection of parents and trees in Eucalyptus full-sib progeny tests

This study aimed to evaluate the efficiency of early selection for parents and trees for cloning in full-sib progeny tests of Eucalyptus spp. The 61 hybrid progenies were evaluated in the north, northwest and central state of Minas Gerais, Brazil, in a randomized complete block design with three replications, in 2001. The trait circumference at breast height (CBH) was evaluated 30 and 84 months after planting in five-plant rows. The selection efficiency was assessed by the fluctuation of genetic and phenotypic parameters, coincidence index, genetic correlation, phenotypic correlation, Spearman rank correlation, correlated response, gain per year and repeatability of phenotypic values at the plant level. All methodologies indicated that early selection is effective both in the selection of parents and the selection of trees for cloning.

Prediction of maize single-cross performance by mixed linear models with microsatellite marker information.

We evaluated the potential of the best linear unbiased predictor (BLUP) along with the relationship coefficient for predicting the performance of untested maize single-cross hybrids. Ninety S(0:2) progenies arising from three single-cross hybrids were used. The 90 progenies were genotyped with 25 microsatellite markers, with nine markers linked to quantitative trait loci for grain yield. Based on genetic similarities, 17 partial inbred lines were selected and crossed in a partial diallel design. Similarity and relationship coefficients were used to construct the additive and dominance genetic matrices; along with BLUP, they provided predictions for untested single-crosses. Five degrees of imbalance were simulated (5, 10, 20, 30, and 40 hybrids). The correlation values between the predicted genotypic values and the observed phenotypic means varied from 0.55 to 0.70, depending on the degree of imbalance. A similar result was observed for the specific combining ability predictions; they varied from 0.61 to 0.70. It was also found that the relationship coefficient based on BLUP provided more accurate predictions than similarity-in-state predictions. We conclude that BLUP methodology is a viable alternative for the prediction of untested crosses in early progenies.

Estabilidade de produção de híbridos simples e duplos de milho oriundos de um mesmo conjunto gênico

The objective of the present work was to study the adaptability and stability of single and double-crosses of maize originated from the same gene pool. Ten commercial single-crosses and all possible double-crosses, obtained from a complete diallel, were evaluated. Seeds of the double-crosses were obtained in an experimental area of the Biology Department at Universidade Federal de Lavras (DBI/UFLA). The experiments were conducted in 15 environments in the 2005/06 growing season, on farms and in experimental stations. The cultural practices were the ones normally used by farmers or experimental stations for maize. The entries were evaluated in randomized complete blocks design with three replications per environment. The trait under study was husked ears yield (kg ha-1), corrected to 13% of moisture content. Nonparametric statistics were used to study hybrids adaptability and stability. The contribution of each hybrid to the genotype-by-environment interaction and the deviation in relation to the maximum performance in each environment was determined. The double-crosses were on average more stable, although some single-crosses were as stable as the double-crosses.

Evaluation of maize top crosses under two nitrogen levels

Maize crops in Brazil have a wide diversity of management systems. There is a large contingent of family agriculture, which uses little or no agricultural inputs, compared to the rural enterprise which uses the most modern production systems. This difference in the management systems is particularly noticeable in relation to consumption of fertilizers, especially nitrogenous ones. Therefore it is necessary to obtain plants with efficient nitrogen (N) use that also respond to applied nitrogen. Thus, the aim of the study was to evaluate the performance of S0:1 progenies, in top crosses, under two nitrogen levels and select the best ones based on responsiveness and efficiency. Sixty seven S0:1 progenies from populations of single cross hybrids were crossed with two testers (T1 - single cross hybrid; T2 - population per se). A hundred and thirty four hybrid progenies plus ten controls were evaluated in two field trials with different levels of nitrogen (one with average levels - 50 kg ha-1 of N - and the other with low levels of nitrogen - 25 kg ha-1 of N) in a 12 x 12 triple lattice design. It is possible to identify and to select progenies from commercial single cross hybrids that are efficient and responsive to nitrogen application. The non-additive effect was as important as the additive effect for grain yield under different nitrogen levels.