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United States Department of Agriculture

Agricultural Research Service

Research Project: PECAN CULTIVATION AND DISEASE MANAGEMENT

Location: Fruit and Nut Research

Title: Use of standard area diagrams to improve assessment of pecan scab on fruit

Authors
item Bock, Clive
item Yadav, Nalini V -
item DE Vos, Stephanie -
item Wood, Bruce

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 6, 2011
Publication Date: June 1, 2011
Citation: Bock, C.H., Yadav, N.S., De Vos, S.M., Wood, B.W. 2011. Use of standard area diagrams to improve assessment of pecan scab on fruit. Phytopathology. 101:S196.

Interpretive Summary: Pecan scab (Fusicladium effusum) causes yield loss of pecan throughout the southeastern US. Poor disease assessment is inaccurate, imprecise, with poor repeatability and reproducibility resulting in misleading data analysis, so accurate, precise assessments are important for comparing treatments to manage disease. Raters assessed 2 sets of images of pecan fruit valves infected with pecan scab and estimated the area diseased. The first set of images (E1) was assessed without using standard area diagrams (SADs), while the second set (E2) was assessed using a SAD set (10 black and white images of known disease severity). Estimates of E1 and E2 were compared to the actual disease severity, determined by image analysis. Use of the SADs improved rater precision, accuracy and repeatability of visual estimates of scab severity among raters.

Technical Abstract: Pecan scab (Fusicladium effusum) causes significant economic losses of pecan throughout the southeastern US. Disease assessment relies on visual rating of disease severity, which can be inaccurate, imprecise, with poor repeatability and reproducibility. Accurate, precise assessments are important for comparing treatments to manage disease. A total of 26 raters assessed 2 sets of 40 images of pecan fruit valves infected with pecan scab and estimated the area diseased. The first set of images (E1) was assessed without using standard area diagrams (SADs), while the second set (E2) was assessed using a SAD set comprised of 10 black and white images of known disease severity. Estimates of E1 and E2 were compared to the actual disease severity, determined by image analysis. Use of the SADs improved rater precision, accuracy and repeatability among raters. Linear regression showed that rater precision improved between the unaided and SAD-aided assessments (r2=0.44-0.94 and r2=0.84-0.95, respectively). Lin’s concordance correlation coefficient ('c) demonstrated improved agreement as a result of using the SAD set ('c=0.28-0.95 for E1 compared to 'c=0.68-0.96 for E2), and rater bias measured by location (µ) and scale (') shifts was reduced using SADs (E1, µ =-0.17-1.57; ' =1.01-1.53 and E2, µ =-0.08-0.84; ' =0.95-1.22, respectively). SADs improve rater estimates of pecan scab severity on fruit.

Last Modified: 9/10/2014
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