Diagrammatic scale for assessing foliar symptoms of alternaria brown spot in citrus

Abstract

Alternaria brown spot (ABS) is the main fungal disease of mandarins. Cause damage to fruits, branches and leaves. For determinations of disease severity in fruit, there is a specific diagrammatic scale, which does not occur for foliar lesions. In order to standardize leaf reviews of ABS in citrus, a diagrammatic scale was developed from the collection of symptomatic Dancy tangerine and Murcott tangor leaves, with ten levels, from zero to 97% of the area damaged by the pathogen. They were tested by five evaluators who analyzed 100 pictures of symptomatic leaves with and without the use of the proposed scale. To validate the scale, precision and accuracy of assessors in rating the images were compared. Results showed that the use of the scale improved the accuracy of the evaluators, with increased accuracy. This shows that the leaf scale can be used to determine the severity of alternaria brown spot in citrus.