RESEARCH ARTICLE Development and Validation of a Diagrammatic Scale for Estimation of Cashew Blight for Epidemiological Studies

Cashew (Anacardiumoccidentale L.) blight is caused by the fungal pathogen Cryptosporiopsis spp. The objective of this study was to develop a scale based according to Weber-Fechner’s visual acuity law, considering the lowest and highest limits of severity observed in the field. A diagrammatic scale with six levels of disease severity (0.1-3.0; 3.1-6.0; 6.1-12.0; 12.1-25.0; 25.1-50.0; 50.1-75.0%) was developed to assess cashew blight severity, caused by the fungus Cryptosporiopsisspp. Scale validation was performed by six raters (three inexperienced and three experienced), who estimated the severity of 48 cashew leaves showing blight symptoms, with and without the use of the scale. Precision and accuracy were determined by linear regression, relating the assessments using the scales to actual severity. Actual severity was assessed with the software Scion image. With the scale, the raters obtained better accuracy and precision levels, although the tendency to overestimate was maintained. Experienced raters were more accurate and precise than inexperienced raters, and assessment improvements with the use of the scale were more significant for inexperienced raters. Two evaluations were performed on the same set of leaves, but in a different sequence order, by the same raters. Using the diagrammatic scales, some raters were able to improve precision and accuracy. Therefore, we could conclude that the diagrammatic scale presented here was suitable for evaluating cashew blight severity.

[1]  M. A. Noronha,et al.  Elaboração e validação de escala diagramática para a cercosporiose do pimentão , 2006 .

[2]  F. W. Nutter,et al.  Improving the accuracy and precision of disease assessments : selection of methods and use of computer-aided training programs , 1995 .

[3]  James G. Horsfall,et al.  Chapter 6 – Pathometry: The Measurement of Plant Disease , 1978 .

[4]  Forrest W. Nutter,et al.  Disease Assessment Concepts and the Advancements Made in Improving the Accuracy and Precision of Plant Disease Data , 2006 .

[5]  Lourenço,et al.  Escala diagramática para a quantificação do complexo de doenças foliares de final de ciclo em soja , 2004 .

[6]  Godoy,et al.  Diagrammatic scales for bean diseases : development and validation , 1997 .

[7]  P. Souza,et al.  Progresso da cercosporiose (Cercospora coffeicola Berkeley & Cooke) em cafeeiros sob cultivos orgânico e convencional , 2008 .

[8]  R. B. Bassanezi,et al.  Elaboração e validação de escala diagramática para avaliação da severidade da mancha preta em frutos cítricos , 2004 .

[9]  J. Kranz,et al.  Measuring Plant Disease , 1988 .

[10]  Laurence V. Madden,et al.  Introduction to Plant Disease Epidemiology , 1990 .

[11]  Marcelo Giovanetti Canteri,et al.  Diagrammatic scale for assessment of soybean rust severity , 2006 .

[12]  R. T. Sherwood.  Illusions in Visual Assessment of Stagonospora Leaf Spot of Orchardgrass , 1983 .

[13]  P. Schaberg,et al.  Factors influencing red expression in autumn foliage of sugar maple trees. , 2003, Tree physiology.

[14]  Paul G. Schaberg,et al.  An instructional guide for leaf color analysis using digital imaging software , 2005 .

[15]  M. Makobe,et al.  Effect of environmental conditions on the growth of Cryptosporiopsis spp. causing leaf and nut blight on cashew (Anacardium occidentale Linn.) , 2013 .

[16]  T. Hsiang,et al.  Quantifying Fungal Infection of Plant Leaves by Digital Image Analysis Using Scion Image Software , 2022 .