Control of bacterial spot of tomato and activation of enzymes related to resistance by chemicals under field conditions
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The control of tomato bacterial spot by the application of chemicals was evaluated on field condition during two trials. Thirty days after transplanting and every 14 days the tomato plants PA-529 hybrid were sprayed with acibenzolar-S-methyl (2.5 g·100 L-1), fluazinam (25 g·100 L-1), pyraclostrobin (8 g·100 L-1), pyraclostrobin + metiram (20 g·100 L-1 + 220 g·100 L-1), copper oxychloride (25.20 g·100 L-1), mancozeb + copper oxychloride (88 g·100 L-1 + 60 g·100 L-1), oxytetracycline (40 g·100 L-1) and water (control), totaling five applications during the crop cycle. Forty days after transplanting, the plants were inoculated with a Xanthomonas perforans isolate (107 UFC·mL-1), disease severity was assessed (10, 19, 29, and 36 days after inoculation), and the area under the disease progress curve was calculated. All chemicals controlled the disease, but better results for total mass and number of fruit was obtained for fluazinam, pyraclostrobin, pyraclostrobin + metiram, copper oxychloride, and mancozeb + copper oxychloride in the first trial, and pyraclostrobin and pyraclostrobin + metiram in the second trial. The average fruit weight, °Brix, pH and total acidity were not affected by the application of the chemicals. The enzymatic activity of the polyphenol oxidase and peroxidase was higher in the first trial, but in the second, only the polyphenoloxidase had the highest activity in the treatments with acibenzolar-S-methyl, pyraclostrobin, and pyraclostrobin + metiram on tomato leaves. Products containing pyraclostrobin increased the activity of some enzymes without reducing the productivity.