André Humberto de Brito

Efeito da cercosporiose no rendimento de híbridos comerciais de milho

Effect of Gray leaf spot on yield of Commercial Maize Hybrids With the objective of quantifying the effect of gray leaf spot (Cercospora zeae-maydis) on yield of 12 commercial maize hybrids and of correlating grain yield reduction with disease severity, two experiments were performed at two sowing dates (November 11 th and December 23 rd , 2005) in the experimental area of the Federal University of Lavras (UFLA), Lavras, MG, Brazil. Disease control in healthy plots of all hybrids was obtained through two applications of epoxiconazol + pyraclostrobin – 37.5 + 99.75 g i.a.ha -1 ) at a 15-day interval. In uncontrolled plots, epidemic development started from natural inoculum present in the area. Eight evaluations of disease severity based on visual symptoms were performed at seven-day intervals from the 60 th day after maize emergence, ranging from 1 (resistant) to 9 (susceptible). The area under the disease progress curve (AUDPC) was estimated and grain yield per plot was also obtained. Results of damage percentage and correlations between grain yield and damage percentage with the estimates of the AUDPC were supported by the data. Damage intensity varied according to sowing season and hybrid, with an average of 13.3%. Maize gray leaf spot reduces the corn grain yield, mainly in the late sowing season, and the use of resistant hybrids excludes the chemical control of the disease. Additional keywords: Zea mays, damage, disease evaluation, fungal disease.

Adubação nitrogenada, densidade de semeadura e espaçamento entre fileiras na cultura do milho em sistema plantio direto

Among the practices and techniques employed for obtaining increased corn yield, the choice of plant arrangement and time of nitrogen topdressing are among the most important, associated with the choice of the hybrid and cropping system. The objective of this trial was study in no-tillage system, the influence of four times of application of nitrogen fertilization associated with three sowing rates and two interrow spacings for two corn cultivars in south Minas Gerais. On the site, two experiments in no-tillage system were established, the first one being set up with the spacing of 0.45 m and the second spacing of 0.90 m. In each experiment, two corn cultivars (P 30K75 and TORK), three sowing rates (55 thousand, 70 thousand and 85 thousand plants ha-1) and four times of application of nitrogen fertilization: 40 kg ha-1 of N applied on the occasion of sowing without any nitrogen topdressing; 40 kg ha-1 of N at sowing + 120 kg ha-1 of N topdressed soon after sowing; 40 kg ha-1 of N at sowing + 60 kg ha-1 of N topdressed at the stage of 4 to 5 leaves + 60 kg ha-1 of N topdressed at the stage of 7 to 8 leaves, 40 kg ha-1 of N at sowing + 120 kg ha-1 of N topdressed at the stage of 6 to 7 leaves. Nitrogen fertilization done into covering, in one or two applications influences in the height of the plants, the height of insertion of the ear and provides significant increases in corn grain yield.

AVALIAÇÃO DA SEVERIDADE DA CERCOSPORIOSE E RENDIMENTO DE GRÃOS EM HÍBRIDOS COMERCIAIS DE MILHO

The large-scale production of Baculovirus to control fall armyworm, Spodoptera frugiperda, presents many limitations. The most important limiting factor is that the baculovirus, which infects fall armyworm, causes liquefaction of the integument immediately after death. This disruption of the integument difficultates the large scale production because dead insect must be frozen before being harvested. This fact implies in high lab work need, increasing the cost of the biopesticide. This problem was overcome by the discovery of a new baculovirus nucleopolyhedrovirus (NPV) isolate in Cascavel/PR, that doesn’t cause liquefaction of the integument (isolate 6NR) immediately after the insect death. This is an extremely important factor in a large-scale baculovirus production. In addition, mortality caused by isolate 6NR on 6-day-old-larvae was above 93% (SEM=0.7%), the average weight dead larva was 116.21 mg (SEM=22.9), the larval equivalent and weight equivalent/ha were 15.04 g (SEM=1.2) and 140.32 larvae (SEM=20.1), respectively.

Reação de híbridos de milho e comparação de métodos para avaliação da Cercosporiose e Mancha Branca

With the objective of evaluating the resistance level of commercial corn hybrids and comparing the efficiency of the estimates of the area under the disease progress curve (AUDPC) and that of the phenotypical stability parameters in the evaluation of resistance maize white spot and gray leaf spot, three experiments were carried out in the agricultural year of 2007/2008 in three environments. Twelve commercial maize hybrids were used, in a randomized block experimental design with three replications. Five evaluations of disease severity (maize white spot and gray leaf spot) based on visual symptoms were performed at seven-day intervals from the 80th day after maize emergence, ranging from 1 (highly resistant) to 9 (highly susceptible). The area under the disease progress curve (AUDPC) was estimated, as were the phenotypical stability parameters, i.e., the linear regression coefficient (bi) between the independent variable evaluation time (x), and the dependent variable, disease severity (y) and the determination coefficient (R2). It was found that in the case of maize white spot and maize gray leaf spot, both methodologies used proved to be effective in the discrimination of the resistance level of the hybrids, enabling them to be ranked in a similar way. The most resistant hybrids to maize white spot and maize gray leaf spot were AG7088, AG 7010 and 2B707, and the most susceptible were 30F44, 30F53 and AG8021. The 30K64, DKB177, DKB390 and Impacto hybrids showed variable levels of resistance with the environment.

Efeito da altura de corte das plantas na produtividade de matéria seca e em características bromatológicas da forragem de milho

Este trabalho foi conduzido com o objetivo de avaliar a producao de materia seca e a composicao bromatologica da forragem de cultivares de milho submetidos a duas alturas de corte das plantas (altura 1 - 0,1 m e altura 2 - 0,8 m) em tres anos de cultivo no municipio de Lavras, MG. Os experimentos foram instalados em area experimental do Departamento de Agricultura da Universidade Federal de Lavras (UFLA) nas safras agricolas 1998/1999, 1999/2000 e 2000/2001, empregando-se cinco cultivares de milho no primeiro ano e seis nos anos seguintes. Os experimentos foram conduzidos sob o delineamento de blocos casualizados em esquema fatorial 5 x 2 e 6 x 2, sendo cinco ou seis cultivares de milho e duas alturas de corte, com tres repeticoes. Avaliaram-se as caracteristicas produtividade de materia seca (MS) e teores de proteina bruta (PB), fibra em detergente neutro (FDN) e fibra em detergente acido (FDA) na MS. Detectou-se efeito significativo das alturas de corte em todas as caracteristicas estudadas. Os teores de PB aumentaram e os de FDN e FDA diminuiram com a elevacao da altura de corte das plantas. Comparando-se as duas alturas de corte, verificou-se que houve uma reducao de 3,3 t.ha-1 na produtividade de MS, um aumento de 0,6% no teor de PB, uma reducao de 4,4% no teor de FDN e uma reducao de 3,9% no teor de FDA com a elevacao da altura de corte de 0,1 para 0,8 m. Os resultados obtidos permitiram concluir que a elevacao da altura de corte, embora tenha contribuido para a diminuicao da producao de MS, proporcionou uma melhoria na qualidade da forragem em decorrencia da parte mais fibrosa e menos digestivel da planta de milho nao ter sido colhida.

Controle químico da Cercosporiose, Mancha-Branca e dos Grãos Ardidos em milho

Este trabalho foi realizado com o objetivo de avaliar os efeitos da aplicacao de fungicida, no controle da Cercosporiose e da Mancha-Branca do milho, e suas consequencias na produtividade de graos e na incidencia de graos ardidos, alem de estabelecer a relacao existente entre a produtividade de graos e a severidade dessas doencas. Dois experimentos distintos (com Azoxystrobina + Cyproconazole e tratamento controle) foram conduzidos em tres locais, no ano agricola de 2007/2008. Utilizaram-se 12 hibridos comerciais de milho, que foram avaliados em delineamento de blocos casualizados, com tres repeticoes. Foram realizadas cinco avaliacoes da severidade das doencas Cercosporiose e Mancha-Branca, por meio de escala de notas, variando de 1 (altamente resistente) a 9 (altamente susceptivel). Estimou-se a area abaixo da curva de progresso da doenca (AACPD). A aplicacao de fungicida e eficiente no controle de doencas foliares e na reducao da incidencia de graos ardidos, alem de proporcionar 12% de aumento na produtividade de graos, em relacao a do tratamento controle. As doencas foliares Cercosporiose e Mancha-Branca reduzem a produtividade de graos de milho e essa reducao e maior quando as doencas ocorrem mais precocemente. A Cercosporiose provoca maior reducao na produtividade de graos, quando comparada com a Mancha-Branca.

Bayesian inference to study genetic control of resistance to gray leaf spot in maize.

Gray leaf spot (GLS) is a major maize disease in Brazil that significantly affects grain production. We used Bayesian inference to investigate the nature and magnitude of gene effects related to GLS resistance by evaluation of contrasting lines and segregating populations. The experiment was arranged in a randomized block design with three replications and the mean values were analyzed using a Bayesian shrinkage approach. Additive-dominant and epistatic effects and their variances were adjusted in an over-parametrized model. Bayesian shrinkage analysis showed to be an excellent approach to handle complex models in the study of genetic control in GLS, since this approach allows to handle overparametrized models (main and epistatic effects) without using model-selection methods. Genetic control of GLS resistance was predominantly additive, with insignificant influence of dominance and epistasis effects.

Genetic control of resistance to gray leaf spot of maize in tropical germplasm

The main goal of this study was to assess the nature and magnitude of gene effects for resistance to Cercospora leaf spot. A randomized block design with three replications was used. The data were obtained at the plant level by assessing the disease severity. The data were analyzed per experiment, using the average data per plot. A dominant-additive genetic model without epistasis was considered, with estimation of the components of means and variance. The genetic control of resistance to gray leaf spot is polygenic with predominance of the additive effects. Dominance was observed in a few small-effect loci and high heritability values.

Consequências da remoção do limbo foliar em diferentes estádios reprodutivos da cultura do milho em duas épocas de semeadura

Em areas tropicais ha poucas informacoes disponiveis sobre o efeito da desfolha em milho, principalmente quando ocorre no periodo do enchimento de graos. Objetivou-se neste trabalho avaliar os efeitos da remocao do limbo foliar durante o periodo de enchimento de graos. Os experimentos foram instalados em 12/11/2005 e 21/12/2005 utilizando-se os hibridos GNZ 2004 e P 30F33. O delineamento experimental utilizado foi o de blocos casualizados com tres repeticoes, em esquema fatorial, sendo duas posicoes de desfolha (acima e abaixo da espiga), duas porcentagens de desfolha (50% e 100%) e quatro estadios reprodutivos (R1, R2, R3 e R4), mais um tratamento adicional, no qual nao foi realizada a retirada das folhas. A remocao do limbo foliar acima da espiga resultou em maiores perdas na producao de graos em relacao a remocao do limbo abaixo da espiga. O efeito da remocao do limbo foliar nao variou com os estadios fenologicos considerados. Os efeitos na produtividade de graos, da remocao do limbo foliar abaixo da espiga foram similares a remocao de 50% do limbo foliar acima da espiga em todos estadios fenologicos considerados. O efeito da remocao do limbo foliar sobre a porcentagem de plantas acamadas e quebradas foi de pequena magnitude.