Development and validation of a severity scale for assessment of fig rust

Abstract

Standardized methods for quantifying rust severity (Cerotelium fici) on fig leaves (Ficus carica L.) are required, so this study aimed to develop and validate a diagrammatic scale to assessment the severity of this disease. Fig leaves that exhibited varying severities of rust symptoms were collected in the field. The actual severity, maximum and minimum limits, and intermediate levels of the scale were determined based on the frequency distribution of the severity values found in the field. In validation of the scale, eight evaluators estimated the severity in 50 leaves with different levels of symptoms with and without the use of the diagrammatic scale. Accuracy and precision of the data were evaluated, and linear regression was used to assess the repeatability and reproducibility of the estimates. The use of the diagrammatic scale provided adequate results for the parameters analysed when compared assessments made without use of the scale, confirming reliability of the estimates to evaluate rust severity on fig leaves.