Development and validation of a standard area diagram set to assess blast severity on wheat leaves
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This study aimed to develop and validate a standard area diagram set (SADS) to quantify the severity of blast, caused by Pyricularia oryzae, on wheat leaves. The SADs has ten levels: 0.1, 1, 5, 10, 22, 32, 42, 52, 62 and 72 % blast severity. To validate the SADs, 12 inexperienced raters estimated disease severity on 50 images of leaves from cultivars BR-18 (susceptible) and BRS-229 (partially resistant). Blast severity was first estimated without the use of the SADs on 50 leaves with a range of blast severity. The same raters evaluated the same 50 leaves using the SADs as an aid. The SADs improved accuracy (coefficient of bias, C b = 0.88 and 0.99, without and with SADs, respectively) and agreement (Lin’s concordance correlation coefficient, ρ c = 0.84 and 0.96 without and with SADs, respectively) of the estimates of severity. The absolute error was (-) 52 % without the SADs and (-) 24 % when using SADs as an aid. Severity estimates were more reliable when using SADs (R2 = 0.87 unaided and R2 = 0.92 with SAD). The SADs proposed in this study will improve accuracy and reliability of estimates of blast severity on wheat leaves.
KeywordsEpidemiology Disease assessment Pyricularia oryzae Triticum aestivum
F.A. Rodrigues thank the National Counsel of Technological and Scientific Development (CNPq) for his fellowship. Mrs. Jonas A. Rios, D. Debona, and H. S. S. Duarte were supported by CNPq. We are grateful to Dr. C. H. Bock for his help with the statistical analysis. This study was supported by grants from CAPES, CNPq and FAPEMIG to Prof. F. A. Rodrigues.
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