Validation of a diagrammatic severity scale to quantify Botrytis fabae damage in faba bean

Background/Objective. Faba bean production (Vicia faba) in the Toluca Valley has been considerably affected by Botrytis fabae, therefore, it is necessary to have a diagrammatic severity scale designed to validated and to quantify its damage. Materials and Methods. 150 leaflets were collected, extracted from three commercial plantations, a visual preselection was carried out based on the presence of symptoms. 138 leaves were digitized to quantify the value of the real damage with the APS PRESS ©Assess 2.0 software. A first visual evaluation (without diagrammatic scale) of the leaves with different degrees of damage was carried out by 20 inexperienced evaluators. A second evaluation was carried out with 10 evaluators, but with support from the scale. The obtained values were analyzed by means of a simple regression. Results. A diagrammatic scale was generated consisting of 6 classes 0(0) 1(0.1-10.0), 2(10.1-20.0), 3(20.01-35.0), 4(35.01-58.0), 5(58.01-100). The results obtained of the simple linear regression, by evaluator, showed for the non-scale evaluation, values of r2 (accuracy) between 0.07-0.78, 1 (precision)=0.0001-0.85 and among evaluators 1 (reproducibility)=0.16-1.54. In contrast, the scale evaluation showed values of r2 =0.88-0.99, 0=0.0001-0.93 8 (by evaluator), and 1=<0.0001 (significant to slope 1.0). These results supported scale validation, respect to its accuracy, precision and reproducibility. Conclusion. A reliable six-classes diagrammatic logarithmic scale was successfully developed and validated to assess disease severity of chocolate spot caused by Botrytis fabae.