Bacterial spot of pepper and tomato is caused by Xanthomonas campestris pv vesticatoria and the disease continues to be economically important in tropical and subtropical regions of the world. The disease is most severe in climates where high rainfall and high temperatures occur concomitantly. Diseased plants have reduced growth and yield compared to healthy plants. Infections on young plants reduce yields more than infections on mature plants. Diseased fruit may be rejected from commercial sales.

Conventional methods of control of bacterial spot have not been very effective. In tropical and subtropical regions the pathogen is endemic, surviving on volunteer plants, or on crop plants in continuous culture. The use of preventive sprays does not adequately control bacterial spot. The combination of three resistance genes into one commercial pepper line, and two resistances into one commercial tomato line is being researched, but this is a very long-term path to a solution.

An integrated approach of control is being used to minimize economic losses to bacterial spot. A biological control strategy would be a welcome addition to the integrated approach.

Another race of X. campestris pv vesicatoria on tomato was detected for the first time at three locations in Florida in a survey of tomato crops in 1991. The new strains were designated as "T race 3". Strains of "T race 3" may have been introduced into Florida on tomato seeds. Since 1991, the incidence of strains of "T race 3" have increased each year. In the 1992-93 seasons, 24 of 283 cultures collected were "T race 3". Strains of "T race 3" from 11 different fields inhibited a strain of "T race 1", and 5 "T race 3" strains inhibited 10 "T race 1" strains. Strains of "T race 3" did not inhibit other "T race 3" strains. The "T race 3" strains are antagonistic to the pepper races in vitro.

The importance of active antagonistic substances in biological control has been well established in research, but many other possibilities exist for different mechanisms of antagonism than those already identified. This CBAG research project was directed toward establishing evidence based on genetics and the importance of the inhibitory compounds produced by "T race 3" strains in the competitive advantage of "T race 3" over "T race 1" strains.

Impacts

• The combination of genetic resistance and biocontrol activity of nonpathogenic strains of tomato race 3 may contribute greatly to control of bacterial spot of tomato. This would allow tomato farmers in Florida to be more competitive in the world market.
  
• During the 1994-95 seasons in Florida, 49,000 acres of tomato were planted and provided $461,000,000 to the growers. It is estimated bacterial spot averages 10 percent loss in yields of tomato in Florida through decreased fruit size resulting from defoliation, and through loss of quality resulting in culled fruit. This means the same amount of fruit for market could be produced on 10 percent less acreage, or about 5000 acres. The average cost per acre of production of tomatoes in Florida is about $9,000. Therefore, about $45,000,000 could be saved by the tomato industry in Florida if bacterial spot can be eliminated.
  
• It is estimated that the results of this research could reduce the incidence of bacterial spot by one half. By reducing the present 10 percent loss to 5 percent, a cost savings to Florida growers of about $22,500,000 could be achieved.