Standard area diagram set for anthracnose severity on grapevine bunches and shoots

Anthracnose is one of the most destructive grapevine diseases in warm and humid regions, but no efficient tools are available to quantify disease symptoms in different parts of the plant. Therefore, this study aimed to develop and validate standard area diagrams (SADs) to evaluate grapevine anthracnose on the fruit and shoot. For fruit SAD development, fruit clusters showing signs of anthracnose symptoms were sampled from five different white grape genotypes: Aromera, Bronner, GF24, Felicia and Helios. To develop the shoot SAD, plants from a population that segregated for anthracnose resistance were artificially inoculated. Fruits and shoots with characteristic symptoms were photographed, and a total of 30 and 31 images, respectively, were selected to develop each SAD. The SADs from fruit and shoots included severity ranging from 0.5 to 17.6% and from 0.8 to 45.9%, respectively. In order to verify the applicability of both SADs, random raters evaluated the images with and without the use of the SAD. Rater data were utilized for validation of both SADs using linear regression, absolute error and Lin’s statistic, and repeatability was tested by inter-rate analysis. The developed SADs improved the accuracy and repeatability among the raters. In addition, diagrammatic scales for anthracnose severity on the fruit and shoot decreased absolute error and disease overestimation. In conclusion, the use of both sets of SADs improved grapevine anthracnose evaluation on the fruit and shoots.