Resumo -A correta avaliação das doenças de plantas é de fundamental importância para os estudos epidemiológicos e para as estratégias de controle das mesmas. A escala diagramática de doenças além de contribuir para a correta avaliação fornece um padrão de uniformidade aos diferentes avaliadores. O objetivo deste trabalho foi desenvolver e validar a escala diagramática para quantificação da severidade da Mancha Branca em folhas de milho. Para a construção da escala, utilizaram-se os limites de severidade mínima e máxima da doença observados, sendo os níveis intermediários da escala definidos por acréscimos logarítmicos, obedecendo a "Lei do estímulo de Weber-Fechner". A escala é composta por sete níveis de severidade: 1,1; 2,1; 4,2; 7,9; 14,4; 25,0 e 39,7%, a qual foi validada por dez avaliadores sem experiência na quantificação da Mancha Branca em milho. Primeiramente, a severidade da doença foi estimada pelos dez avaliadores sem auxílio da escala, e em seguida, com a utilização da escala proposta, em 30 folhas de milho, com níveis de severidade heterogêneos. Regressões lineares simples relacionando os valores das severidades reais e severidades estimadas foram utilizadas para análise da acurácia dos avaliadores, enquanto os coeficientes de determinação e variância dos erros absolutos determinaram a precisão dos avaliadores. Constatouse precisão nas estimativas visuais de severidade da doença pelo uso da escala diagramática. A escala diagramática proposta é adequada para estimar a severidade da Mancha Branca em folhas de milho, sendo possível sua utilização em pesquisas epidemiológicas. Palavras-chave -Pantoea ananatis S. Phaeosphaeria maydis (P. Henn.). Doenças foliares do milho.Abstract -Precise evaluation of plant diseases is very important for epidemiology studies and elaboration of control strategies. The diagrammatic scale of diseases contributes for an accurate evaluation and supplies an uniform standard for different evaluators. The objective of this work was to develop and validate a diagrammatic scale to quantify the severity of maize white foliar spot disease. In order to build the scale, minimum and maximum severity extremes of the disease were set by observation, and the intermediate levels were defined by logarithmic increment, according to "Weber-Fechner law of stimulus". The scale is composed by seven levels of severity: 1.1; 2.1; 4.2; 7.9; 14.4; 25.0 and 39.7%, which were validated by evaluators (10) without any experience in maize white spot disease quantification. Thirty leaves of corn with heterogeneous levels of the disease were analyzed and the severity was estimated by the evaluators, at first, without the scale and then, prior to that, with the proposed scale. Simple linear regressions relating the real values of severity and the estimated severities were used for the accuracy analysis of the evaluators, while the coefficients of determination and variance of absolute errors determined the precision of the evaluators. Visual estimation of severity was precise with the use of the diagramma...
The objective of this work was to evaluate the effect of foliar spraying with bacterial biocontrol agents (BBAs) on the control of common bacterial blight (CBB) of bean, and on the induction of systemic resistance in bean plants. CBB control by BBAs was evaluated by spraying bean leaves 48 and 24 hours before and after pathogen inoculation (BPI and API, respectively), with: DFs93, Bacillus cereus; DFs513, Pseudomonas veronii; DFs769, B. cereus; the C01 combination, DFs93 + DFs769 + DFs831 (Pseudomonas fluorescens); the C03 combination, DFs348 (Bacillus sp.) + DFs769 + DFs831; and water (control). Systemic effects were analyzed after spraying DFs513, DFs769, C03, and water 72 and 48 hours BPI. Phaseolin production induced by DFs348, DFs513, DFs769, DFs831, and water was also assessed. DFs513, DFs769, and C03 significantly reduced disease incidence (area under disease progress curve), regardless of spraying time and disease severity when sprayed 72 and 48 hours BPI. The DFs769 and DFs831 isolates induced the accumulation of phytoalexin (phaseolin). Therefore, DFs513, DFs769, and C03 show potential for the biocontrol of CBB when applied preventively on bean leaves, besides inducing systemic resistance.
The aim of this study was to evaluate the effect of the incorporation of canola residue in soil for controlling cucumber damping-off caused by Pythium aphanidermatum. Canola residues at increasing amounts (30 to 120 t ha −1) were incorporated into infested plots and covered with doublefaced plastic. After 10 days, soil samples were taken from each plot to evaluate inoculum concentration and percent of seedling emergence. Chemical analysis of leaves and soil and microbial activity (MA) and electrical conductivity (EC) was performed 40 days after seedling emergence. Seedling emergence, MA and EC increased with the increase of canola residue amount. Moreover, the rate of soil nutrients and potassium also increased. Seedling damping-off and inoculum levels decreased with increasing levels of canola residue. In the field, seedling emergence and MA also increased with increasing levels of canola residue incorporated four months earlier. Soil biofumigation with canola residue proved an effective tool for managing cucumber damping-off. Soil cover with plastic can be reduced to 10 days without compromising disease control.
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