Measuring Disease Progress in Pure and Mixed Stands of Plant Cultivars

Abstract

Gumpert, F.-M. 1989. Measuring disease progress in pure and mixed stands of plant cultivars. Phytopathology 79:968-973. A measure is presented that quantifies disease progress of fungal The rate of disease increase is particularly useful if the epidemiological pathotypes during the exponential phase of the epidemic. This measure, parameters display compensatory effects. The second application deals referred to as rate of disease increase (p), represents the factor by which with the long-term composition of pathotype mixtures. The pathotype the number of infection units is multiplied from one day to another after with the largest p value will predominate in the long run. This is again the initial infection waves have damped. The rate of disease increase exemplified by using barley leaf rust data. The third application concerns depends on four pathotype/cultivar-specific parameters (latent period, disease control strategies. A host stand should be composed so that the infectious period, infection efficiency, spore production rate) and two corresponding predominant pathotype has a p value smaller than the nonspecific parameters (deposition frequency and autodeposition prevailing pathotype of any other composition. This concept does not frequency). Three applications are given. First, it is used to determine presuppose selection against unnecessary genes for virulence. A condition the levels of partial resistance of barley cultivars to leaf rust. The calculated is given under which a cultivar mixture may be more beneficial than p values were highly correlated both with total spore production per each of its components grown in pure stands, and this condition is unit leaf area (r - 0.97) and with disease score in the field (r = 0.81). illustrated by a simple example of two pathotypes and two cultivars. Additional keywords: autoinfection, epidemiology, optimal cultivar composition. Plant pathologists mostly use Van der Plank's (29) apparent infection unit, independently of its phase of development, is infection rate (r) to quantify disease progress. This measure has counted here. Infection units that have passed the latent period proven useful for comparative studies on sanitation efforts, are called lesions. Our model, referring to a single pathotype, fungicide application, and cultivar resistance (3,8-10,15). It was has the following form: shown by Van der Plank (29) that r exhibits wavelike behavior during epidemic development even though latent period (p),