Diagrammatic scales use to improve the accuracy of the Grape Ripe Rot severity evaluations

Efficient disease management to prevent and minimize damage requires analytical tools such as diagrammatic scales, which are essential for phenotypic analyses and epidemiological studies. The effectiveness of this model for quantifying damage and symptoms depends on its accuracy and precision in the analyses, which are evaluated using sta­tistical indices. There is no specific diagrammatic scale (DS) for grape ripe rot. Therefore, this study aimed to create and validate a specific DS for laboratory analysis of this disease. The scale was developed using the R software, based on the NGRDI (Normalized Green Red Difference Index), using photographs of berries with different disease percentages. Based on the Weber-Fechner law of visual acuity, the soft­ware calculated the limits of the scale, generating a scale with 12 levels of severity (0 to 91.4%). To validate the DS, 24 berries of different grapevine genotypes were inoculat­ed with two isolates of Colletotrichum spp. On the tenth day, the berries were evaluated by 13 random raters who gave a score in the percentage of the affected area for each infected berry, with and without the help of the scale developed. Lin’s Concordance Correlation (CCC) and the R² Coefficient of determination provided similar results in terms of a correlation coefficient; higher values with the use of the DS compared to the visual evaluation of the severity of grape ripe rot without any reference. Looking for discrepancies and errors of assessment, the Inter-Rate Reli­ability Index and the Absolute Error Adherence also agreed in terms of higher variation and high error without the use of DS to evaluate the severity of grape ripe rot. Therefore, the DS can be used routinely in studies with grape ripe rot on white-colored berry varieties. However, adjustments to the model are necessary for red and pink ones.