-Several studies addressing the inoculation of cereals with diazotrophic microorganisms can be found in the literature. However, in many experiments, investigators have overlooked the feasibility of applying these microorganisms to the furrow together with the seed, and the effect of bacterial concentration on phytostimulation. The aim of this work was to evaluate the effect of doses of an inoculant based on Azospirillum brasilense, applied to the seed furrow when planting maize, combined with different doses of nitrogen fertiliser. The experiment was carried out in the field, in soil of the cerrado region of Brazil. An experimental design of randomised blocks in bands was adopted, comprising nitrogen (40, 100, 200 and 300 kg ha -1 ) and doses of an A. brasilense-based liquid inoculant applied to the seed furrow (0, 100, 200, 300 and 400 mL ha -1 ). The dose of 200 mL ha -1 Azospirillum was noteworthy for grain production. This is the first report of the effective application of Azospirillum in the seed furrow when planting maize in the cerrado region of Brazil.
Resumo -O objetivo deste trabalho foi avaliar genótipos de milho quanto à resistência ao acamamento e ao quebramento do colmo e apresentar metodologia para avaliar essas características. Os ensaios foram realizados em blocos ao acaso, com 85 genótipos tropicais de milho e quatro repetições, em cinco locais. Foram avaliadas: as forças necessárias para o arranquio da planta e para o quebramento do colmo e o ângulo no momento do quebramento. As medições foram realizadas com equipamentos desenvolvidos para essas finalidades. Foram realizadas análises de variância e teste de Scott-Knott quanto às características. As forças de arranquio da planta, de quebramento do colmo e ângulo no momento do quebramento do colmo interagiram significativamente com a localidade. As médias variaram de 49,43 a 76,03 kgf para a força de arranquio da planta, de 1,07 kgf a 2,76 kgf para força de quebramento do colmo, e de 16,15 a 41,18º para o ângulo de quebramento do colmo. Existe variabilidade genética para seleção quanto à resistência ao acamamento e ao quebramento do colmo em genótipos tropicais de milho. A metodologia apresentada é eficiente para a avaliação e discriminação de genótipos.Termos para indexação: Zea mays, avaliação de genótipo, metodologia de avaliação. Resistance to lodging and culm breakage in tropical cornAbstract -The objective of this work was to evaluate corn genotypes for resistance to lodging and to culm breakage and to describe a new method for evaluating these traits. Assays were carried out in randomized blocks, with 85 tropical genotypes of corn and four replicates in five localities. The force required to pull out the plant and to break the culm and the breaking angle of momentum were evaluated. The measurements were made with equipment developed specifically for this purpose. Variance analyses and the Scott-Knott test were carried out for the traits. The forces required to pull out the plant and break the culm, and the breaking angle for the culms were significantly interactive with the locality. The means varied from 49.43 to 76.03 kgf for the force required to pull out the plants, from 1.07 to 2.76 kgf for the force required to break the culm, and from 16.15 to 41.18º for the angle at the breakage of the culm. There is genetic variability for selection for resistance to lodging and culm breakage in tropical corn. The method described is efficient for evaluating and differentiating the genotypes.Index terms: Zea mays, genotypic evaluation, evaluation methodology. IntroduçãoNa produção mundial de milho são estimadas perdas anuais de 5 a 20%, em consequência do acamamento e do quebramento do colmo (Instituto FNP, 2007). Os efeitos desses caracteres sobre o rendimento de grãos dependem principalmente do genótipo, da severidade e da fase de desenvolvimento da cultura em que eles se manifestam (Federizzi et al., 1994).O acamamento pode ser definido como um estado permanente de modificação da posição do colmo em relação à posição original, o que resulta em plantas recurvadas e até mesmo na quebra de colmos. O pr...
IIIQuantificação da área foliar e efeito da desfolha em componentes de produção de milho
Resumo -O objetivo deste trabalho foi avaliar a influência da desfolha do milho no desenvolvimento e na produtividade de grãos. Seis ensaios foram conduzidos em diferentes safras e locais e em dois níveis de produtividade. Utilizou-se o delineamento de blocos ao acaso, com sete repetições. A desfolha foi realizada no estádio vegetativo V 4 do milho (quatro folhas expandidas), e os tratamentos foram: remoção das duas folhas basais, remoção das quatro folhas expandidas, remoção total das folhas (secção da parte aérea) e testemunha (sem desfolha). Foram avaliados: duração do período vegetativo; e, em pré-colheita, altura de planta, altura de espiga, percentagem de plantas acamadas, força de quebramento de colmo, força de arranquio da planta e produtividade. A remoção das quatro folhas e a remoção total aumentaram a duração do período vegetativo e reduziram a altura de planta, a altura de espiga e a resistência do colmo ao quebramento. Esses níveis de desfolha também reduziram a produtividade, principalmente com a remoção total das folhas. A força de arranquio da planta não foi influenciada pela desfolha. A retirada de quatro folhas e do total das folhas reduz a produtividade de grãos, respectivamente, em 6,25 a 14,05% nos híbridos avaliados.Termos para indexação: Zea mays, área foliar, integridade foliar, período vegetativo, potencial produtivo. Grain development and yield in maize subjected to defoliation levelsAbstract -The objective of this work was to evaluate the influence of defoliation of maize on grain development and yield. Six trials were conducted in different growing seasons and locations and at two yield levels. A randomized complete block design was used, with seven replicates. Defoliation was made at the V 4 vegetative stage of maize (four expanded leaves), and treatments consisted of: removal of the two basal leaves, removal of the four expanded leaves, total removal of leaves (aerial plant section), and a control (without defoliation). The following were evaluated: length of the vegetative period; and, at pre-harvest, plant height, ear insertion height, plant lodging percentage, stalk-breaking strength, force required to pull the plant, and yield. The removal of four leaves and the total removal of leaves increased the length of the vegetative period and reduced plant height, ear insertion height, and stalk strength against breaking. These defoliation levels also reduced yield, mainly with the total removal of leaves. The force required to pull the plant was not influenced by defoliation. Removal of four leaves and of all leaves reduces grain yield, respectively, in 6.25 to 14,05 in the evaluated hybrids.Index terms: Zea mays, leaf area, leaf integrity, vegetative period, yield potential. IntroduçãoO potencial produtivo da cultura do milho (Zea mays L.) é definido por volta dos estádios V 4 e V 5 , de quatro a cinco folhas expandidas, respectivamente, em razão da diferenciação floral (Ritchie et al., 1993). Nesse período, a planta origina os primórdios do pendão e da espiga, e também ocorre a difer...
The effect of leaf area reduction on corn plants during the reproduction phaseReduction in leaf area in corn plants during reproduction changes physiological metabolism and consequently the accumulation of dry matter in grains. The aim of this work was to study changes in agronomic characteristics caused by defoliation in corn during the reproduction phase. The experiment was carried out in Uberlândia, Minas Gerais state, in the agricultural year 2007/2008. The experiment was arranged in a randomized block design, consisting of seven treatments: control without defoliation, removal of two apical leaves, removal of four apical leaves, removal of all leaves above spike, removal of four intermediate leaves, removal of all leaves below spike, and removal of all plant leaves, with five repetitions. The genotype used for the evaluations was hybrid NB 7376. Defoliation was carried out when plants were at the growth stage R 2 . The variables assessed were: yield, density of spikes and corncobs, root resistance and stem integrity. When all leaves above the spike were removed, grain yield was reduced by 20%. Corncob density, stem integrity and root resistance to uprooting were also affected. Spike density was only affected when all plant leaves were removed. The leaf area remaining physiologically active above the spike was found to be most efficient in terms of grain yield.
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