October
2008
, Volume
92
, Number
10
Pages
1,394
-
1,399
Authors
Warren E.
Copes
,
USDA-ARS Southern Horticultural Laboratory, Poplarville, MS 39470
; and
Katherine L.
Stevenson
,
Department of Plant Pathology, University of Georgia, Tifton, GA 31793
Affiliations
Go to article:
RelatedArticle
Accepted for publication 27 June 2008.
Abstract
ABSTRACT
A pictorial key was developed and the relationship between disease severity (S) and incidence (I) was examined to aid in the assessment of black root rot of pansy caused by Thielaviopsis basicola. The key consisted of photographs of root segments that represented nine disease severity levels ranging from 1 to 91%. Pansies that had received different fertility treatments, as part of seven separate experiments, were inoculated with T. basicola. Four weeks after inoculation, roots were washed, and incidence and severity of black root rot were visually assessed using a grid-line-intersect method. Disease incidence ranged from 1.3 to 100%, and severity ranged from 0.1 to 21.4% per plant. Four different mathematical models were compared to quantitatively describe the I-S relationship for the combined data from all seven experiments. Although all models provided an adequate fit, the model that is analogous to the Kono-Sugino equation provided the most reliable estimate of severity over the entire range of disease incidence values. The predictive ability and accuracy of this model across data sets was verified by jackknife and cross-validation techniques. We concluded that incidence of black root rot in pansy can be assessed more objectively and with greater precision than disease severity and can be used to provide reliable estimates of disease severity based on derived regression equations that quantify the I-S relationship for black root rot.
JnArticleKeywords
Additional keywords:
Chalara basicola,
disease intensity,
disease measurement,
rating scale
Page Content
ArticleCopyright
The American Phytopathological Society, 2008