Elaboração e validação da escala diagramática para avaliação da mancha branca do milho

Abstract

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...

Development of a diagrammatic scale for the evaluation of postharvest physiological deterioration in cassava roots

“…Using the PPD scale, the evaluators improved the accuracy levels for severity estimates, as observed by other authors who evaluated dendrophama blight in strawberry (Mazaro et al, 2006), gray mold in castor bean (Sussel et al, 2009), and maize white spot (Malagi et al, 2011). Some studies have shown some variability among evaluators using the same scale; therefore, assessments of accuracy and precision are greatly influenced by the ability of each evaluator to estimate the inherent severity (Nutter Jr. & Schultz, 1995), and can be affected by factors such as the complexity of the severity to be assessed, as for cassava, and as the different types of PPD in their shapes and colors.…”

Accuracy and Reliability of Severity Estimates Using Linear or Logarithmic Disease Diagram Sets in True Colour or Black and White: a Study Case for Rice Brown Spot

“…; Malagi et al. ; Sachs et al. ), there is limited evidence whether coloured diagrams are superior to black and white drawings in regard to accuracy and reliability of estimates (Angelotti et al.…”

“…Although image analysis tools have fostered the development of disease diagrams with enhanced realism (Bock et al 2010), most of disease diagrams reported to date are simple drawings of leaves in two contrasting colours such as black (for the diseased area) and white (for the healthy area). While some are represented with images of actual leaves in true colour (Halfeld-Vieira and Nechet 2006;Salgado et al 2009;Soares et al 2009;Malagi et al 2011;Sachs et al 2011), there is limited evidence whether coloured diagrams are superior to black and white drawings in regard to accuracy and reliability of estimates (Angelotti et al 2008).…”

Elaboration and validation of a diagrammatic scale to assess downy mildew severity in grapevine

“…These scales can be used to standardize the severity estimation and reduce the subjective of disease severity visual estimates. The diagrammatic scales is expected to be easy and quick for a wide range of conditions with reproducible, accurate, and precise results (MALAGI et al, 2011;SACHS et al, 2011;SANTOS et al, 2011;YADAV et al, 2012). Accuracy refers to how faithful an estimate is from the actual amount of the evaluated disease, while precision corresponds to the confi dence and/or repeatability associated to such estimate (NUTTER JR. & SCHULTZ, 1995, ANGELOTTI et al, 2008MICHEREFF et al, 2009).…”