Disease severity assessment in epidemiological studies: accuracy and reliability of visual estimates of Septoria leaf blotch (SLB) in winter wheat

El Jarroudi, Moussa and Kouadio, Louis ORCID: https://orcid.org/0000-0001-9669-7807 and Mackels, Christophe and Tychon, Bernard and Delfosse, Philippe and Bock, Clive H. (2014) Disease severity assessment in epidemiological studies: accuracy and reliability of visual estimates of Septoria leaf blotch (SLB) in winter wheat. In: 2014 APS-CPS Joint Meeting, 9-13 Aug 2014, Minneapolis, MN, U.S.A..


Several methods are available to measure the severity of Septoria leaf blotch (SLB) of winter wheat but differ in accuracy, reliability, ease of use and rapidity. The accuracy and reliability of visual assessments of SLB severity by raters was determined by comparison with assumed actual values obtained by digital image analysis. Raters included one plant pathologist with extensive experience of visual disease assessment, and three other raters who were trained prior to field observations using standard area diagrams and the software DISTRAIN. Initially analyses were performed using SLB severity over the full 0-100% range; subsequently, to explore error over short ranges of the 0-100% scale, the scale was divided into sequential 10%-increments (i.e., 0-10%, 10-20%,…90-100%) 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 (ρc) = 0.92-0.99). However, agreement between actual SLB severities and the estimates by raters was less good when compared over the short intervals of the 10×10% classes (ρc = -0.12-0.99, depending on the percentage class and the experiment), demonstrating that agreement will vary depending on the actual disease range over which it is compared. Inter-rater reliability over the full 0-100% range measured using correlation analysis was high between each pair of raters (r = 0.970 to 0.992, P<0.0001), which was confirmed by the inter-class correlation coefficient (ρ ≥ 0.927). This study provides new insight into using a full range of actual disease severity versus 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.

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Item Type: Conference or Workshop Item (Commonwealth Reporting Category E) (Poster)
Refereed: No
Item Status: Live Archive
Additional Information: Abstract only.
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 15 Jun 2021 06:16
Last Modified: 30 Aug 2021 03:01
Uncontrolled Keywords: Septoria leaf blotch
Fields of Research (2008): 07 Agricultural and Veterinary Sciences > 0703 Crop and Pasture Production > 070308 Crop and Pasture Protection (Pests, Diseases and Weeds)
Fields of Research (2020): 30 AGRICULTURAL, VETERINARY AND FOOD SCIENCES > 3004 Crop and pasture production > 300409 Crop and pasture protection (incl. pests, diseases and weeds)
Identification Number or DOI: https://doi.org/10.1094/PHYTO-104-11-S3.1
URI: http://eprints.usq.edu.au/id/eprint/42212

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