Diagrammatic logarithmic scales for assess the severity of spotted leaves and calyces of roselle

Abstract

Spotted leaves and calyces of roselle (Hibiscus sabdariffa L.) induced by Corynespora cassiicola, is currently considered the main disease for this crop in Mexico. Given its importance, it is necessary to have a standardized method to quantify the disease severity. Therefore, the objective of this study was to develop and validate two diagrammatic logarithmic scales to quantify the severity of this disease. Naturally infected roselle leaves and calyces were collected in Guerrero state commercial plantations, and the actual severity of each of these organs was assessed. The proposed scales, designed from 2LOG program, comprised six classes in leaves: 0=0, 1=(>0-2-4), 2=(>4-7-12), 3=(>12-19-29), 4=(>29-42-57) and 5=(>57-70-≤100); in calyces: 0=0, 1=(>0-3-5), 2=(>5-10-18), 3=(>18-30-46), 4=(>46-63-77) and 5=(>77-87-≤100). The accuracy, precision and reproducibility of the estimates were verified. For leaves and calyces, one evaluation was carried without scale, and two others evaluations were done with scale, each seven days apart. Evaluators showed better levels of accuracy, precision and reproducibility with the scales. The results suggest that the proposed scales are appropriate to estimate the severity of spotted leaves and calyces of roselle.