Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 19, 2012
Publication Date: April 1, 2013
Citation: Yadav, N.S., De Vos, S.M., Bock, C.H., Wood, B.W. 2013. Development and validation of standard area diagrams to aide assessment of pecan scab symptoms on pecan fruit. Plant Pathology. 62:325-335. 2013. Interpretive Summary: Pecan scab (Fusicladium effusum) causes losses of pecan nutmeat yield and quality in the southeastern U.S. Estimates of disease severity are needed for several purposes, including estimating crop loss relative to disease severity, comparing treatments in experiments, comparing relative susceptibility of cultivars, study of pathogen epidemiology, predicting disease development, and in surveying. Disease assessment relies on visual rating, which can be inaccurate, imprecise with poor inter-rater reliability. A standard area diagram (SAD) set for pecan scab on fruit valves was developed to assist in the process of disease assessment and increase accuracy and precision of estimates, and inter-rater reliability thereby ensuring better quality data. The SAD set was shown to significantly improve all measures of disease assessment without any increase in time spent. This SAD set should be a useful tool for aiding assessment where greater accuracy, precision and repeatability of pecan scab rating is required, including comparing disease management treatments and studies of disease epidemiology.
Technical Abstract: Pecan scab (Fusicladium effusum) causes losses of pecan nutmeat yield and quality in the southeastern U.S. Disease assessment relies on visual rating, which can be inaccurate, imprecise with poor inter-rater reliability. A standard area diagram (SAD) set for pecan scab on fruit valves was developed. Two sets of 40 images of diseased fruit valves with known severity were assessed by 26 raters. The raters assessed the first set without SADs, but used the SADs as an aide for the second. SADs significantly improved rater precision (correlation coefficient, r = 0.90 and 0.95 without and with SADs), accuracy (correction factor, Cb = 0.84 and 0.96, without and with SADs) and agreement (Lin’s concordance correlation coefficient, 'c = 0.76 and 0.91 without and with SADs) with true values and inter-rater reliability (intra-class correlation coefficient, ' = 0.79 and 0.95 without and with SADs, respectively). The least accurate and precise raters improved the most. Experienced raters had significantly higher precision compared to inexperienced raters, but only when using the SAD set. There was no significant difference in time to assess images either without or with SADs, but there was a slight tendency for faster raters to assess slower, and slower raters to assess faster when using SADs. Two raters who misused the aide still assessed with greater accuracy and precision compared to not using it. SADs improve rater estimates of pecan scab severity on fruit, and this SAD set should be useful for assessment where greater precision, accuracy and inter-rater reliability are required.