Standard area diagrams to assess scab severity of entire‐margined leaves of sour passion fruit

Abstract

Scab caused by the Cladosporium cladosporioides complex is one of the most important diseases affecting passion fruit yield and fruit quality. Standard area diagrams are useful tools to improve the accuracy and reliability of the estimates of disease severity in many pathosystems. The interpretation of the accuracy of the resulting disease data may be the basis for providing better disease management. This study aimed to develop and validate standard area diagrams (SADs) to quantify scab severity of entire‐margined leaves of sour passion fruit plants. The SADs are composed of ten images of scab severity values (0.4%, 3.5%, 5.4%, 8.0%, 11.1%, 16.2%, 26.1%, 38.2%, 47.9% and 58.9%). Twenty raters (ten experienced and ten inexperienced ones) evaluated the SADs. The raters estimated the same set of fifty images twice. In the examination, the SADs were used, while in the second examination, they were not used. Accuracy was significantly improved by using the SADs. The coefficients of bias (Cb) were 0.96 and 0.98 for the experienced raters and 0.75 and 0.98 for the inexperienced raters without and with SADs, respectively. The correlation coefficient (r) values were 0.95 and 0.97 for the experienced raters and 0.89 and 0.97 for the inexperienced raters without and with the use of the SADs, respectively. Lin's concordance correlation coefficient (ρc) values were 0.91 and 0.95 for the experienced raters and 0.66 and 0.95 for the inexperienced raters without and with the use of the SADs, respectively. Moreover, the coefficient of determination (R2) significantly improved when the SADs were used. The SADs proposed in this study, if properly used, may improve both the accuracy and reliability during the evaluation of scab severity of entire‐margined leaves of sour passion fruit plants.

How much do standard area diagrams improve accuracy of visual estimates of plant disease severity? A systematic review and meta-analysis

“…Indeed, linear regression continues to be used by some phytopathometrists for evaluating SADs (Santos et al 2017;Camara et al 2018;Trojan and Pria 2018;Arias et al 2020;Robaina et al 2020;Kublik et al 2020). The two linear regression coefficients (intercept and slope), together with the coefficient of determination (R 2 ), are usually reported for each rater in the SAD validation study, while those phytopathometrists reporting LCCC statistics have most often reported means of all raters combined (Del Ponte et al 2017;Bock et al 2020;Brás et al 2020;Nascimento et al 2020;Rivera et al 2020;Castellar et al 2021;Montero et al 2021).…”