Bacterial leaf spot of lettuce

Bacterial leaf spot of lettuce caused by ''Xanthomonas campestris pv. vitians'' was first described in the United States by Nellie Brown in 1918 from diseased lettuce in South Carolina and Virginia. The disease was first reported in California in 1964. It has since been reported from the major lettuce growing regions worldwide probably due to contamination of seed. In addition to survival on seed, the pathogen can survive in fields in plant debris and on leaves of symptomless weeds during fallow periods between lettuce crops.

Symptoms
There are two discrete symptoms associated with bacterial leaf spot and head rot. The first include watersoaked, brown lesions that later turn black about 1-2mm (⅛in) in diameter occur. These lesions become V-shaped, translucent, and collapse. Lesions may expand along the veins of the plant. The second type of symptom consists of small black spots scattered along the leaf surface.

Treatment
There are no recommended bactericides. Pesticides allowed on other vegetables for control of bacterial diseases may reduce disease severity by only 50% of that observed on non-treated plants. Moreover, the use of some copper bactericides can cause symptoms of phytotoxicity on lettuce plants.

Prevention
For controlling bacterial leaf spot of lettuce, différent approaches must be considered. An integrated disease management program should include the use of résistant cultivars of lettuce, seed treatments, an early detection of the bacterium on seedlings, and a biological and/or chemical control to reduce the pathogenic bacterial population in greenhouses.