The objective of this study was to evaluate the effects of the drift of ripeners (sulfometuron-methyl, ethephon and trinexapac-ethyl) on the initial growth of Eucalyptus urograndis. The experimental design was a randomized block with seven treatments (control; sulfometuron-methyl 0.9 and 1.2 g i.a. ha -1 ; ethephon 28.8 and 38.3 g i.a ha -1 ; trinexapac-ethyl 15 and 20 g i.a. ha -1 ) with four replicates using each plant as an experimental plot. We evaluated the effects 7, 14, 21, 28, 35 and 42 days after application, when we determined the length, diameter, total leaf area and total dry mass of the stem. The application of sulfometuron-methyl may have resulted in an effect known as "hormesis" due to an increasing trend in stem growth. The application of trinexapac-ethyl resulted in greater increases in the leaf dry mass and leaf area compared with those caused by the other ripeners that were used in this study, most likely due to the loss of apical dominance. The application of ethephon had no significant effect on the plants.

No abstract

Young eucalyptus seedlings in general are sensitive to stress factors during early development and establishment. Weed competition is one of the major biotic effects contributing to reductions on the initial growth of eucalyptus plants. This study aimed to evaluate the effects of different densities and distances of Urochloa decumbens seeded and regrowth during the early growth of Eucalyptus urograndis. Two experiments were conducted in an open and semi-controlled area, in a completely randomized design, in factorial arrangement 4 x 2 + 1, being respectively, four densities of weed plants (2.6, 5.2, 7.8 and 10.4 plants m -²), two distances between Eucalyptus and weeds (5 and 15 cm), and a weed-free control. The height and diameter of eucalyptus were evaluated 15 days intervals, and at the end of 90 days after eucalyptus planting (DAP) the leaf area and dry mass were measured. For a density of U. decumbens plants that were seeded at a density of 2.6 plants m -2 , 90 days after Eucalyptus planting (DAP), there was a decrease in the height (20%), stem diameter (10%), leaf area (55%) and dry mass (48%). For the regrowth of U. decumbens at a density of 2.6 plants m -2 at 90 DAP, the height (47%), stem diameter (55%), leaf area (89%) and dry mass (87%) decreased. The results demonstrate that U. decumbens adversely affected the growth of eucalyptus, without statistical differences between distances, and weeds in regrowth affecting Eucalyptus growth more than seeded weeds.

Rotating crop cultivars with different resistance genes could slow the evolution of virulent strains of fungal pathogens, but could also produce highly virulent pathogen strains. We present a new model that links polycyclic pathogen epidemiology and population genetics in order to predict how different strategies of rotating cultivars with different resistances will affect the evolution of pathogen virulence and the breakdown of crop resistance. We modelled a situation where there were four different resistance genes that can be deployed within each crop cultivar, and four virulence genes that may be present within the pathogen. We simulated four different rotational management strategies: (i) no rotation; (ii) a different gene every year; (iii) a different gene every 5 years; and (iv) a different combination of two stacked genes each year. Results indicate that rotating cultivars can lead to longer periods of disease suppression but also to the selection of highly virulent strains. The efficacy and relative advantage of different resistant cultivar rotation strategies depended on the fitness penalties, initial virulence allele frequencies, and ability of non-virulent pathogen genotypes to grow and reproduce on resistant cultivars. By capturing the essential processes involved, our model provides a useful new tool for investigating the evolutionary dynamics of pathogen virulence and crop resistance breakdown.

Plantas de eucalipto são sensíveis à interferência imposta pela comunidade infestante, principalmente durante o crescimento inicial, período que compreende o primeiro ano após a instalação da cultura. Sendo assim, o presente estudo objetivou avaliar o efeito de densidades crescentes de Commelina benghalensis L. (trapoeraba) sobre o crescimento inicial de plantas de Eucalyptus grandis Hill (ex Maiden) em duas estações do ano (inverno e verão). Foram realizados dois experimentos, um no inverno (durante 90 dias) e outro no verão (durante 120 dias), em área aberta, semicontrolada, em caixas de 70 L. Para ambos os experimentos utilizou-se delineamento em blocos casualizados, com quatro repetições e os tratamentos consistiram de densidades crescentes de trapoeraba: 0 (testemunha), 4, 8, 16, 20, 28, 36, 40, 60 e 80 plantas m-2. Quinze dias após o plantio das mudas de trapoeraba, foi plantada uma muda de eucalipto no centro de cada caixa. Ao final dos períodos experimentais, foram avaliados a altura, o diâmetro, a área foliar e a massa seca da parte aérea do eucalipto. Observou-se que a partir de 4 plantas m-2 já houve interferência negativa no crescimento do eucalipto, com reduções de 38,4% na área foliar e 35% na massa seca, no inverno; e reduções de 52,9% na área foliar e 64,7% na massa seca, no período de verão. Conclui-se que a partir da densidade de 4 plantas m-2 há interferência no crescimento do eucalipto e que, no período de verão, a planta daninha apresenta comportamento competitivo mais agressivo, causando maior interferência nas plantas de eucalipto.

The aim of this study was to evaluate the response of eucalyptus plants submitted to the application of glyphosate increasing rates. The doses 0.0, 3.6, 7.2, 18, 36, 72 and 180 g ha -1 of acid equivalent (ae) of glyphosate were applied on plants. At 7, 15, 22, 29, 36 and 42 days after application (DAA) was determined leaves relative chlorophyll content and quantum efficiency of photosystem II. At 22 and 42 DAA plant height and stem diameter were measured. At 42 DAA were determined the leaves dry mass, stem dry mass and foliar area. The height, diameter, leaves and stem dry masses and foliar area were converted to percentages, whereas the controls as 100%. These variables were fitted to the model described by Gauss equation. The data chlorophyll content and quantum efficiency of photosystem II were submitted to mean comparison, and when they differed, we performed the Tukey test at 5% probability. All the features presented here showed some hormetic effect promoted by reduced rates of glyphosate and the increments observed in these characteristics (when compared to control) ranged between 5.92 and 33.18% at 42 DAA. From average curve with height, diameter, leaves dry mass, stem dry mass and foliar area can be concluded that the increase averaged 12% on application of 16 g a.e. of glyphosate ha -1 . For leaves chlorophyll content significant differences were observed only at 29 DAA, while for quantum efficiency of photosystem II significant differences were found only at 7 DAA.

No abstract

Reguladores vegetais e herbicidas atuam e modificam diversos processos metabólicos nas plantas. A aplicação de doses sub-letais destes compostos pode ser utilizada de modo a modular o desenvolvimento e o crescimento das plantas, um efeito denominado homesis. Múltiplos estudos tem relatado o efeito promotor de doses sub-letais de etil-trinexapac no acúmulo de biomassa e na expansão da área foliar de plantas de eucalipto. Até o presente momento, não há recomendação acerca de doses promotoras e/ou inibidoras de processos metabólicos para a cultura do eucalipto. Desta forma, este trabalho tem como objetivo investigar o efeito de doses crescentes de etil-trinexapac no estabelecimento e crescimento inicial de mudas de Eucalyptus urograndis. Etil-trinexapac foi aplicado em doses de 15 à 90 g de ingrediente ativo por hectare (g i.a. ha-1) em duas modalidades através da pulverização ou da imersão das raízes em solução. As doses de 15 g i.a. ha-1 via pulverização, e 30 g i.a. ha-1 via imersão de raízes, resultaram em efeito positivo no crescimento no clone GG100 de Eucalptus urograndis, com acréscimos de, respectivamente, 74,6% e 12,8% na massa seca total, em relação à testemunha. As doses de 15 à 90 g i.a. ha-1 via pulverização resultaram em efeito estimulatório no crescimento do eucalipto. As doses de 15 e 30 g i.a. ha-1, na modalidade imersão das raízes, proporcionaram efeito positivo nas características avaliadas do eucalipto. A dose de 90 g i.a. ha-1 apresentou efeito inibitório ao crescimento do eucalipto na modalidade imersão das raízes, aos 35 dias após a aplicação de etil-trinexapac.