A standard area diagram set for severity assessment of eyespot on rice

Abstract

This study aimed to develop and validate a standard area diagram set (SADs) to estimate the severity of eyespot of rice caused by Drechslera gigantea. For this purpose, a SADs with seven levels of severity (0.3; 1.0; 3.0; 5.0; 10; 15; and 21%) was established. The SADs was validated by 16 raters with no experience in evaluating plant diseases. Both accuracy and precision improved when they used the SADs. The statistical parameters for the 16 raters were: bias coefficient factor - Cb (no SADs = 0.404, with SADs = 0.994); correlation coefficient - r (no SADs = 0.884, with SADs = 0.953); and Lin’s concordance correlation coefficient - ρc (no SADs = 0.356, with SADs = 0.947). In addition, estimates were more reliable: inter-rater coefficient of determination - R2 (no SADs = 0.712, with SAD = 0.873); intra-class correlation coefficient - ρ (no SADs = 0.723, with SADs = 0.924). The SADs proposed here is a useful tool for improving visual assessments of eyespot severity of rice.