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Title: Comparison of Different Assessment Methods for Common Scab from the National Common Scab Trials

Author
item Wanner, Leslie
item Haynes, Kathleen
item THILL, CHRISTIAN - U OF MINN, DEPT HORT SCI
item BRADEEN, JAMES - U OF MINN, DEPT PLNT PATH
item NOVY, RICHARD - USDA/ARS, ABERDEEN, ID
item WHITWORTH, JONATHAN - USDA/ARS, ABERDEEN, ID

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/8/2008
Publication Date: 4/1/2009
Citation: Wanner, L.A., Haynes, K.G., Thill, C.A., Bradeen, J., Novy, R.G., Whitworth, J. 2009. Comparison of Different Assessment Methods for Common Scab from the National Common Scab Trials. Meeting Abstract. American Journal of Potato Research 86:161-162

Interpretive Summary:

Technical Abstract: Common scab (CS), caused by various Streptomyces species, is a serious soil-borne potato disease. Information on CS susceptibility is an important component of all potato breeding programs, but the disease shows widely varying symptoms across environments, complicating assessment of resistance. The purpose of this study was to compare four different assessments of symptoms of common scab on analysis of variance (ANOVA), estimates of broad-sense heritability (H), and significance of pair-wise comparisons. Disease expression from 11 potato clones was evaluated at three locations (ID, ME, MN) in 2002 and 2003. Clones were planted in soil naturally infested with Streptomyces species in a randomized complete block design with three replications. At harvest, tuber surface area infected was rated by the Horsfall-Barratt (HB) rating scale (1-12) and Ueli Merz’ (UM) modified scale that reduces the surface area affected into categories to six unequal divisions with a single category for all tubers with more than 50% area affected. The most severe type of lesion on each tuber was rated on a 0-5 scale. Tubers were also simply classified for the percent that showed CS. Two area indices, one based on the HB (AIHB) and the other on the UM (AIUM) rating scales, and a lesion index (LI) were calculated. Log (AIHB), log (AIUM), log (LI), and the arcsine vproportion scabby tubers were analyzed by the general linear models procedure in SAS and pair-wise comparisons were made between the check varieties and the remaining clones using the pdiff option. ANOVAs were the same for all four assessments: there were significant differences among clones, and the environment x clone interaction was significant. Estimates of H were similar for all four assessments (0.77 to 0.92). Pair-wise comparisons involving log (AIHB) and log (AIUM) agreed 100%, log (AIHB) and log (LI) agreed 74%, log (AIHB) and arcsine vproportion scabby tubers agreed 83%, and log (LI) and arcsine vproportion scabby tubers agreed 71%. These results demonstrate that a simple evaluation of percent scabby tubers is adequate for ANOVA and estimating H but not for pair-wise comparisons. Use of AIUM and LI provided better discrimination for pair-wise comparisons of clones with individual check varieties. (poster, Breeding and Genetics, PAA Membership 137)