A Standard Area Diagram Set to Estimate the Severity of Angular Leaf Spot in the Leaflets of Common Bean: Development and Validation

Abstract

This study aimed to develop and validate a standard area diagram set (SADs) to estimate the severity of angular leaf spot (ALS), caused by the fungus Pseudocercospora griseola, in the leaflets of common bean plants. For the elaboration of SADs, the minimum and maximum disease severity limits in the leaflets were considered, along with the intermediate levels following linear increments. The SADs had 10 levels of severity as follows: 0.5%, 2.2%, 4.5%, 9.6%, 20.1%, 30.8%, 41.2%, 52.1%, 67.4%, and 77.3%. The validation was performed by 20 raters, 10 inexperienced and 10 experienced in quantifying severities of foliar diseases. The severity estimates were obtained in 150 leaflets displaying different levels of severity without and using the proposed SADs. Accuracy, precision and reliability of the estimates were improved using SADs. The SADs obtained in the present study proved to be adequate to estimate the severity of ALS in the leaflets of common bean plants with the potential of use in any study in which it is crucial to quantify the severity of this foliar disease to discriminate treatments with precision and accuracy.