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TECHNICAL SESSION: Population diversity of plant pathogenic bacteria

Distribution and Characteristics of Xanthomonas Species Causing Bacterial Spot in Midwestern Processing Tomatoes
Francesca Rotondo - The Ohio State University, Department of Plant Pathology. David Francis- The Ohio State University, Department of Horticulture and Crop Science, Eduardo Bernal- The Ohio State University, Department of Horticulture and Crop Science, Sally Miller- The Ohio State University, Department of Plant Pathology

Bacterial leaf spot of tomato (BLST) is a disease of both processing and fresh market varieties. Outbreaks cause defoliation and fruit lesions, decreasing yield and marketability. BLST is associated with four species of Xanthomonas (X. vesicatoria, X. euvesicatoria, X. gardneri and X. perforans). Typically outbreaks of BLST within a geographic location are dominated by one of these species. Temporal shifts of the predominant pathogen within geographic locations have been reported in Florida in 1998 (X. euvesicatoria to X. perforans) and in Ohio in 2010 (X. vesicatoria to X. gardneri). Surveys were conducted over six years (2010-2012, 2017- 2018) to determine the distribution of Xanthomonas spp. in Midwestern tomato fields and the sensitivity of 738 isolated strains to copper and streptomycin sulfate was assessed in vitro. Xanthomonas gardneri was the predominant species isolated in 2010, 2011, and 2012 (83%, 75%, and 65%, respectively). By 2017, X. perforans isolations had increased over previous years and was the predominant species isolated from symptomatic tomato fruits by 2018. Resistance to copper sulfate increased in all strains over the survey period. In 2010, all the recovered strains were sensitive to the highest concentration of copper sulfate (200mg/ml). By 2018, over 50% of the recovered strains were resistant. Despite the limited use of streptomycin products in Midwestern processing tomatoes, resistance to streptomycin sulfate was commonly observed.