Incidence-severity relationships in the pathosystem Coffea arabica-Hemileia vastatrix
1999
Silva-Acuna, R. | Maffia, L.A. | Zambolim, L. | Berger, R.D.
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 + 0.000573X2; R2 = 0.87. The leaf area with rust (Y(1a) was also well related with incidence of leaves with rust as Y(1a) = 0.001 -0.01076X + 0.008376X2; R2 = 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 (R2 = 0.97 and 0.96) and for the estimated leaf area with rust (R2 = 0.95 and 0.98). Therefore, the readily determined incidence can be used to estimate both measures of disease severity of coffee rust.
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