Bacterial Leaf Spot of Lettuce: Relationship of Temperature to Infection and Potential Host Range of Xanthomonas campestris pv. vitians

Abstract

Epidemiological aspects, including optimum temperature for infection and host range of Xanthomonas campestris pv. vitians, causal organism of bacterial leaf spot (BLS) of lettuce, were investigated. The optimum temperature for infection was determined to be 22.7°C based on growth chamber studies. Internal populations were monitored over time in lettuce, tomato, pepper, parsley, cilantro, and beet. Each plant species was infiltrated with the bacterium at 105CFU/ml. Highest populations developed in lettuce (108CFU/cm2) followed by pepper with 106CFU/cm2, whereas the other plant species harbored much lower populations (105 to 103CFU/cm2). Infectivity titration endpoints were similar in pepper and lettuce (103 to 104CFU/ml). For other plant species tested, infectivity titration endpoints were 106 to 107 CFU/ml. Electrolyte leakage data and corresponding internal population data support the conclusion that fresh-market tomato is not a host of X. campestris pv. vitians but, instead, interacts in an incompatible response. Electrolyte leakage from cells of tomato plants inoculated with X. campestris pv. vitians or a pepper strain of X. axonopodis pv. vesicatoria peaked at 48 h, suggesting that tomato is not a host for the BLS pathogen. Both electrolyte leakage and population dynamics results point to pepper as a potential host of X. campestris pv. vitians.