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 cultiva rs were combined in different proportions to achieve seven mixture tre atments. Plots were inoculated by transplanting diseased spreader plan ts in the center of each plot. Disease incidence and severity were con sistently lower in the mixtures containing 25 and 50% resistant cultiv ar, whereas a mixture with 10% resistant cultivar was less effective i n controlling bean anthracnose. Disease progress curves for both incid ence and severity were fit to four models (exponential, logistic, mono molecular, and Gompertz). The Gompertz model best described disease pr ogress in all treatments. The rates of disease increase (dy/dt) were a lways lower for mixtures containing the resistant cultivar than for pu re stands of the susceptible cultivars. The Gompertz infection rates ( r) decreased as the proportion of the resistant cultivar in the mixtur es increased and mixture efficacy values increased.