Mixed Genotypes Combined with Copper Sprays to Manage Bacterial Spot of Bell Peppers

Effects of genotype mixtures combined with three copper + maneb spray schedules on bacterial spot (Xanthomonas campestris pv. vesicatoria) of bell peppers were tested from 1993 to 1995. Planting patterns used for mixing the resistant and susceptible genotypes were either rows of resistant plants interplanted in rows of susceptible plants or a checkerboard pattern. In 1993, three races (1, 2, and 3) of the pathogen were used as inoculum, and two races (1 and 2) were used in 1994 and 1995. Interplanting of resistant and susceptible peppers and application of copper sprays resulted in less disease and greater yields. In 1994, the genotype mixtures had 6 to 45% less disease than pure stands of the susceptible genotype with three spray schedules. In 1995, the mixtures had 15 to 44% less disease compared with pure stands of the susceptible genotype without the copper + maneb sprays. Significantly less disease was observed for the susceptible genotype in the checkerboard pattern compared with pure stands of the susceptible genotype during 1994 and 1995. For several of the mixtures, no significant differences in yield between the weekly (7-day) and the biweekly (14-day) spray schedules were observed. There was a tendency for one race of the pathogen to predominate, depending on the host resistance gene(s) present. The checkerboard pattern of mixing genotypes was more effective in reducing disease in the susceptible genotype compared with row patterns. The use of genotype mixtures could be viewed as added insurance against the bacterial spot pathogen, in addition to copper spray programs to prolong the durability of genotypes.