Chemical control of bacteria Xanthomonas hortorum pv. gardneri and Xanthomonas euvesicatoria pv. perforans in vitro

Abstract

Tomato bacterial leaf spot is a worldwide disease that causes high losses in processed and fresh tomatoes. This disease is caused by four species of bacteria (Xanthomonas hortorum pv. gardneri, Xanthomonas euvesicatoria pv. perforans, Xanthomonas euvesicatoria pv. euvesicatoria and Xanthomonas euvesicatoria pv. vesicatoria). Xanthomonas hortorum pv. gardneri and Xanthomonas euvesicatoria pv. perforans are the phytopathogenic bacteria most frequently found in tomato crops. The objectives of this work were to identify potential bactericides and to study the mancozeb and copper oxychloride in the management of bacterial spot caused by Xanthomonas hortorum pv. gardneri and Xanthomonas euvesicatoria pv. perforans. Forty-four active ingredients were tested at 1% of the commercial product (1000g c.p./100L H2O) as first screening. Posteriorly, those that inhibited bacterial multiplication were tested at their recommended doses. When used at a dose of 1000g c.p./100L H2O, the products that inhibited the multiplication of X. hortorum pv. gardneri and X. euvesicatoria pv. perforans were benzalkonium chloride, acetic acid, cuprous oxide, mancozeb, copper hydroxide, mancozeb + famoxadone, copper oxychloride, metiram + pyraclostrobin, Bordeaux mixture and Viçosa mixture. At the doses recommended in the package insert, the products that inhibited the multiplication of X. hortorum pv. gardneri and X. euvesicatoria pv. perforans were benzalkonium chloride, acetic acid, mancozeb, mancozeb + famoxadone and metiram + pyraclostrobin. Copper oxychloride at the recommended dose of 0.2% (200g c.p./100L H2O – 168g a.i./100L H2O) did not inhibit the multiplication of X. hortorum pv. gardneri. It has been estimated that 0.004% is resistant to the recommended dose of copper oxychloride. At doses higher than 0.4% (400g c.p./100L H2O – 336g a.i./100L H2O) there was no bacterial growth. However, once the bacteria grow in a culture medium containing 0.2% copper oxychloride of commercial product (200g c.p./100L H2O – 168g a.i./100L H2O), it can be multiplied in a culture media even at a dose of 1000g c.p./100L H2O (840g a.i./100L H2O), which would be equivalent to a dose of 10kg c.p./ha. Mancozeb inhibited bacterial growth from the dose of 0.1% (100g c.p./100L H2O – 80g a.i./100L H2O). However, when X. hortorum pv. gardneri resistant to copper oxychloride 1% (1000g c.p./100L H2O – 840g a.i./100L H2O) is striated in a culture medium containing mancozeb, the bacteria multiply up to a dose of 0.5% mancozeb (500g c.p./100L H2O – 400g a.i./100L H2O). The in vitro results indicate that doses equal to or less than 0.2% copper oxychloride (200g c.p./100L H2O – 168g a.i./100L H2O) select colonies resistant to high doses of copper oxychloride and also decrease the efficiency of mancozeb.