VIEW ARTICLE

Ecology and Epidemiology

Measuring Disease Progress in Pure and Mixed Stands of Plant Cultivars. Frank -M. Gumpert, Institute for Plant Breeding, Seed Science and Population Genetics, University of Hohenheim, D-7000, Federal Republic of Germany; Phytopathology 79:968-973. Accepted for publication 18 April 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-968.

A measure is presented that quantifies disease progress of fungal pathotypes during the exponential phase of the epidemic. This measure, referred to as rate of disease increase (p), represents the factor by which the number of infection units is multiplied from one day to another after the initial infection waves have damped. The rate of disease increase depends on four pathotype/cultivar-specific parameters (latent period, infectious period, infection efficiency, spore production rate) and two nonspecific parameters (deposition frequency and autodeposition frequency). Three applications are given. First, it is used to determine the levels of partial resistance of barley cultivars to leaf rust. The calculated p values were highly correlated both with total spore production per unit leaf area (r = 0.97) and with disease score in the field (r = 0.81). The rate of disease increase is particularly useful if the epidemiological parameters display compensatory effects. The second application deals with the long-term composition of pathotype mixtures. The pathotype with the largest p value will predominate in the long run. This is again exemplified by using barley leaf rust data. The third application concerns disease control strategies. A host stand should be composed so that the corresponding predominant pathotype has a p value smaller than the prevailing pathotype of any other composition. This concept does not presuppose selection against unnecessary genes for virulence. A condition is given under which a cultivar mixture may be more beneficial than each of its components grown in pure stands, and this condition is illustrated by a simple example of two pathotypes and two cultivars.