Standard area diagram with color photographs to estimate the severity of coffee leaf rust in Coffea canephora

Abstract

Color photographs represent the symptoms of the disease as observed in the field, favoring the visual estimation of severity. In order to increase the accuracy, repeatability and reproducibility of Coffea canephora L. rust severity estimates, this study was carried out to elaborate and validate a standard area diagram (SAD) constructed with color photographs (SADcp). To do so, we collected leaves with different intensities of symptoms in crops, and the actual severity was determined with the aid of the software QUANT. The intermediate levels of the scale were determined based on the frequency distribution of severity values. The validation of the diagram was performed by 13 raters who estimated disease severity in 50 leaves of C. canephora with different intensity of symptoms. One assessment without the standard area diagram and two assessments with the diagram were performed at intervals of seven days. Data were analyzed by linear regression and Lin's concordance correlation coefficient. The accuracy, precision, repeatability and reproducibility of the estimates were evaluated. To compare the efficiency of SADcp with the existing scale constructed with two-color diagram (SAD2col), these procedures were performed with both scales. Without the scale and with the SAD2col diagram, the raters overestimated the severity of the disease. With the use of SADcp, the raters presented better levels of accuracy, precision, reproducibility and repeatability in the estimates, compared to when they did not use SAD, or when they used SAD2col. Therefore, SADcp was suitable for estimating the severity of coffee leaf rust in C. canephora.

Plant phenotyping relevance

コーヒー葉さび病の病徴重症度という植物状態を対象に、カラー写真による標準面積図を開発し、精度・再現性・反復性を検証しているため、植物フェノタイピング手法が中心である。

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