Standard area diagrams for tomato early blight severity assessments on leaves and leaflets

Two standard area diagrams (SADs) were developed to quantify the severity of tomato early blight (EB), caused by Alternaria solani, on leaves and leaflets. The SADs were composed by sets of images with distinct EB severity for leaflets (0–40%) and leaves (0-46.4%). To validate the diagrams, 13 evaluators with no experience in quantifying the plant disease severity estimated EB severity by using a 50-image sample of tomato leaves and leaflets, first without SADs and then using the proposed SADs. The data were submitted to regression analysis and Lin’s concordance correlation coefficient, and the accuracy, precision, repeatability, and reproducibility of the estimates for EB severity were assessed. Based on the parameters of Lin’s coefficients and intraclass correlations, EB severity estimates were consistent and more reliable using SADs, improving evaluators’ performance. The diagrams proposed in this study improved the quantification of EB severity performed by 13 evaluators, increasing the accuracy, precision, and reliability of the estimates. Therefore, the proposed diagrams can be used in further studies on the epidemiology, resistance, and management strategies of this pathosystem.