February
1999
, Volume
83
, Number
2
Pages
186
-
188
Authors
R.
Silva-Acuña
,
Fondo Nacional de Investigaciones Agropecuarias, Bramón; Táchira, Venezuela
,
L. A.
Maffia
and
L.
Zambolim
,
Depto. de Fitopatologia, Universidade Federal de Viçosa, 36571-000, Viçosa, MG, Brasil
, and
R. D.
Berger
,
Plant Pathology Department, University of Florida, Gainesville 32611
Affiliations
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RelatedArticle
Accepted for publication 4 November 1998.
Abstract
ABSTRACT
Incidence-severity relationships for coffee rust were studied to determine if the easily assessed incidence could be used to evaluate host resistance and fungicide treatment. At two locations in each of 3 years, the incidence of rust on 300 leaves was compared with two assessments of severity: (i) the average number of sporulating pustules per leaf, and (ii) the estimated leaf area with rust. For nine or 10 assessments in time at one location and pooled over 3 years, the average number of sporulating pustules per leaf (Y
sp) was well related with the incidence of leaves with rust (X) as Y
sp = 0.02982+ 0.017035X +0.000573X
2; R
2 = 0.87. The leaf area with rust (Y
la) was also well related with incidence of leaves with rust as Y
la = 0.001 − 0.01076X +0.008376X
2; R
2 = 0.92. For two independent data sets from a second location obtained over two seasons, the above models satisfactorily fit the relationships for the average sporulating pustules per leaf (R
2 = 0.97 and 0.96) and for the estimated leaf area with rust (R
2 = 0.95 and 0.98). Therefore, the readily determined incidence can be used to estimate both measures of disease severity of coffee rust.
JnArticleKeywords
Additional keywords:
disease assessment
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© 1999 The American Phytopathological Society