Improving assessments of anthracnose severity on grapevine leaves through the development of a standard area diagram set

Abstract

Anthracnose, caused by Elsinoe ampelina, is an important grapevine disease in humid regions that causes serious crop losses in different parts of the world. The objective of this study was to improve assessments of anthracnose severity on grapevine leaves through the development of a standard area diagram set (SADs). The SADs comprises six true colour diagrams with anthracnose severity ranging from 1.1 to 27.4%. The intermediate values are 2.1, 4.3, 8.3 and 15.6%. To validate the SADs, 12 raters assessed 50 images of grapevine leaves with a range of anthracnose severities. The raters estimated the severity without the use of the SADs, then one week later provided estimates for the same set of images using the SADs as an aid. For all raters, the estimates of grapevine anthracnose severity using the SADs were closer to the actual values than the unaided estimates. Significant improvements in accuracy (coefficient of bias, Cb = 0.90 without the SADs and 0.99 with the SADs), precision (Pearson correlation coefficient, r = 0.89 without the SADs and 0.96 with the SADs) and agreement (Lin’s concordance correlation coefficient, ρc = 0.80 without the SADs and 0.96 with the SADs) were observed. Moreover, the SADs also significantly improved the inter-rater reliability of the estimates (R2 = 0.70 without the SADs and 0.89 with the SADs). The SADs proposed in this study was proven to be adequate for estimates of anthracnose severity on grapevine leaves.