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ARS Home » Southeast Area » Byron, Georgia » Fruit and Tree Nut Research » Research » Publications at this Location » Publication #307012
Title: Disease severity assessment in epidemiological studies: accuracy and reliability of visual estimates of Septoria leaf blotch (SLB) in winter wheat

Author
item EL JARROUDI, MOUSSA - University Of Liege
item KOUADIO, AMANI - Agriculture And Agri-Food Canada
item MACKELS, CHRISTOPHE - University Of Liege
item TYCHON, BERNARD - University Of Liege
item DELFOSSE, PHILIPPE - University Of Luxembourg
item Bock, Clive

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 5/9/2014
Publication Date: 11/1/2018
Citation: El Jarroudi, M., Kouadio, A., Mackels, C., Tychon, B., Delfosse, P., Bock, C.H. 2018. Disease severity assessment in epidemiological studies: accuracy and reliability of visual estimates of Septoria leaf blotch (SLB) in winter wheat [abstract]. Phytopathology. 104:S3.37.

Interpretive Summary:

Technical Abstract: The accuracy and reliability of visual assessments of SLB severity by raters (i.e. one plant pathologist with extensive experience and three other raters trained prior to field observations using standard area diagrams and DISTRAIN) was determined by comparison with assumed actual values obtained by digital image analysis. Initially analyses were performed using SLB severity over the full 0-100% range; then, to explore error over short ranges of the 0-100% scale, the scale was divided into sequential 10%-increments based on the actual values. Lin’s concordance correlation (LCC) analysis demonstrated that all raters were accurate when compared over the whole severity range (LCC coefficient ('c)= 0.92-0.99). However, agreement between actual and visual SLB severities was less good when compared over the short intervals of the 10×10% classes ('c= -0.12-0.99), demonstrating that agreement will vary depending on the actual disease range over which it is compared. Inter-rater reliability between each pair of raters over the full 0-100% range (correlation analysis r= 0.970-0.992, P<0.0001), and inter-class correlation coefficient ('= 0.927) were very high. This study provides new insight into using a full range of actual disease severity vs limited ranges to ensure a realistic measure of rater accuracy and reliability, in addition to contributing to the ongoing debate on the use of visual disease estimates based on the 0-100% ratio scale for epidemiological research.