Management of Bacterial Spot of Pepper and Tomato
The primary management strategy of bacterial spot begins with use of certified pathogen-free seed and disease-free transplants. The bacteria do not survive well once host material has decayed, so crop rotation is recommended. Once the bacteria are introduced into a field or greenhouse, the disease is very difficult to control.
Pepper plants are routinely sprayed with copper-containing bactericides to maintain a "protective" cover on the foliage and fruit (Figure 17). Strains of the pathogen resistant to copper and/or streptomycin are fairly common and can be detected by plating bacteria on media containing these compounds (Figure 18). Genes encoding resistance to copper and streptomycin can be borne on plasmids (extrachromosomal DNA) contained in the bacterial cells. The presence of these genes on plasmids allows for the rapid spread of resistance to other non-resistant bacteria.
Although resistant cultivars are available and widely planted, there are strains of the pathogen able to overcome all of the currently known major resistance genes (Figure 19). Currently, three independently segregating genes form the basis for resistance to bacterial spot in commercial cultivars of bell peppers. Strains of the pathogen that react differently with the resistance genes of the pepper plant are designated as races. With the report of a fourth resistance gene in 1998, 11 races can be differentiated using peppers. Resistance has not been as easy to find and use in tomato. Formerly, four races were recognized that infect tomato. With the proposed taxonomic changes, these have assumed species status (Jones, et al. 2004).
Biological control options for bacterial spot are limited. However, a biological control method that uses bacterial viruses (bacteriophages) that specifically kill the bacterial pathogens is now available. Treatments with these bacteriophages, marketed as “AgriPhage,” have been successful in reducing disease, especially in greenhouse transplant production.