Anthracnose development in mixtures of resistant and susceptible dry bean cultivars

Field experiments were conducted from 1992 to 1994 to characterize the effect of cultivar mixtures on development of bean anthracnose caused by Colletotrichum lindemuthianum. Three light-red kidney bean cultivars were combined in different proportions to achieve seven mixture treatments. Plots were inoculated by transplanting diseased spreader plants in the center of each plot. Disease incidence and severity were consistently lower in the mixtures containing 25 and 50% resistant cultivar, whereas a mixture with 10% resistant cultivar was less effective in controlling bean anthracnose. Disease progress curves for both incidence and severity were fit to four models (exponential, logistic, monomolecular, and Gompertz). The Gompertz model best described disease progress in all treatments. The rates of disease increase (dy/dt) were always lower for mixtures containing the resistant cultivar than for pure stands of the susceptible cultivars. The Gompertz infection rates (r) decreased as the proportion of the resistant cultivar in the mixtures increased and mixture efficacy values increased.