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

Abstract

AbstractScab 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.