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NFREC Extension Report No: 2005-7 October 2005
Recommended Management Strategies for Bacterial Spot on Tomato Caused by Xanthomonas species and Current Reclassification of the Associated Pathogens
Tim Momol, Jeff Jones*, and Steve Olson, University of Florida, IFAS, NFREC, Quincy and *Plant Pathology Department, Gainesville, FL
Introduction Bacterial spot is present wherever tomatoes are grown. This disease thrives during hot, humid, and rainy periods (tropical, sub-tropical, and temperate climates). Causal agent of this disease is previously know as Xanthomonas campestris pv. vesicatoria. Symptoms (Fig 1) and signs ( Fig. 2) can be used to do tentative diagnosis.
Reclassification of the Xanthomonas species associated with bacterial spot Causal agent of this disease is previously know as Xanthomonas campestris pv. vesicatoria. Currently, four distinct Xanthomonas species have been identified which cause bacterial spot on tomatoes and peppers (Jones et al., 2004). Prior to last year, only two species were recognized and included X. vesicatoria (northern U.S.) and X. axonopodis pv. vesicatoria (Race T1 and T3). Extensive analysis of strains from around the world revealed that two more species exist (Jones et al., 2004). As a result of the genetic analyses, two new species have been identified as X. gardneri and X. perforans. Another change was to reclassify X. axonopodis pv. vesicatoria as X. euvesicatoria.
In Florida prior to 1991 the common bacterium associated with tomato for many years was X. euvesicatoria (previously race T1). However, X. perforans (previously race T3) was introduced into Florida and within a short time became the prevalent strain on tomato. In fact in field studies, Jones et al. demonstrated that X. perforans became the dominant strain and displaced X. euvesicatoria. Furthermore, X. perforans produces three bacteriocin-like compounds that are inhibitory to X. euvesicatoria. The other two species, X. vesicatoria and X. gardneri, have not been identified in Florida, but have caused significant problems in South America and in the northern United States. These two species cause significant problems in locations where they exist and potentially could be a concern in Florida.
Bacterial Spot Management Recommendations
Preplant • Consider control of volunteers and solanaceaous weeds (i.e., ground cherry, nightshade) in and around tomato fields • Rotate fields in an attempt to avoid carryover on volunteers and crop residues
Production • Exclude the pathogen by applying strict sanitation practices (pathogen free, seed, transplants, stakes, machinery, etc.). • Do not spray, tie, harvest, or handle plants while they are wet. • Apply Actigard (Syngenta) every 14 days, start early (Label rates). Actigard is a plant activator and induces natural resistance mechanisms (similar to immunization) of host plants. • Apply Agri-phage (OmniLytics) twice a week, start early (Label rates) Bacteriophages (i.e., Agri-phage) are viruses that infect bacteria. Bacteriophages (phages) are providing a biological control method to reduce bacterial spot severity during growing season. Phage populations are negatively impacted by sunlight (UV), and other environmental conditions. These are recommended practices for Agri-phage applications: - use non-chlorinated water in the spray tank - apply just before or after sunset - use powdered-skim milk ( 4 lbs/100 gal) and sugar (2lbs/100 gal) formulation to reduce the effect of UV. Thank mix these with Agri-phage. - Use phages specific to the bacteria in your production area: send bacterial spot samples to OmniLytics every 15-20 days during the growing season to determine the most efficacious phages against the bacteria in your production area and to avoid resistance development to phages. - Phages need to be store in a refrigerator (4 C). - Do not use phages stored from previous season.
• Use copper compounds plus mancozeb mixture (3:1 ai ratio) (Label rates). Copper tolerant strains of the bacteria might be present in your area. Actigard and bacteriophage uses will provide a significant reduction in copper applications. • Application of Tanos (Dupont) (Label rates) alternated with copper +mancozeb help provide bacterial spot suppression. • Another option for biological control is the application of Serenade (AgraQuest) (Label rates) combined with copper compounds to provide bacterial spot reduction.
After harvest • Plow under crop residue immediately. • Start with suitable rotation and cover crops (i.e., rye for winter, sudan-sorghum for summer in north Florida) to avoid volunteers and weeds that support pathogen populations.
Fig. 1. Bacterial spot symptoms on tomato. (Photo Credit, Hank Dankers, University of Florida).
Fig. 2 . Sign of the bacteria: Bacterial ooze (millions of bacterial cells, white cloudy appearance on the image) coming out from bacterial spots. (Photo Credit, Hank Dankers, University of Florida). |
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