Bactericidal potential of Agrochemicals against bacterial leaf spot pathogen Xanthomonas campestris pv. Vesicatoria of tomato prevalent in Nashik region, Maharashtra and ability of bacteria to form pesticide resistant mutant

Selection of suitable agrochemicals/pesticides plays an important role in the management of bacterial plant pathogen prevalent in a given area, may be due to the presence of pesticide resistance available in the pathogen. In this scenario, the assessment of bactericidal potential of agrochemical to be used in the management of bacterial plant pathogen is very necessary. To manage the bacterial leaf spot and blight pathogen Xanthomonas campestris pv. Vesicatoria on tomato prevalent in Nashik region, the bactericidal potential of various agrochemicals were assayed. The bacterial potential of antibiotic Streptomycin sulphate, and Streptocycline; the bactericide Bactericin-100, and the Bordeaux mixture; the copper fungicide Copper-ox chloride and the dithiocarbamate group of fungicide Mancozeb; the combination of Copper ox chloride + Streptocycline were against the tomato leaf spot and blight pathogen Xanthomonas campestris pv. Vesicatoria under in vitro condition. The minimum inhibitory concentration of these agrochemicals against Xanthomonas campestris pv. Vesicatoria varies indicating the variable bactericidal potential of these agrochemicals against the said bacterium prevalent in Nashik areas. The bacterial population of Xanthomonas campestris pv. Vesicatoria was resistant to the antibiotic Terramycin, Streptomycin sulphate and to the fungicide Copper ox chloride, Mancozeb and a combination of Copper ox chloride + Streptomycin sulphate and induced the pesticide resistant mutant in the bacterium with various mutation frequencies. The mutation rate for Terramycin and Streptomycin sulphate was 3.5 x 10-4 and 2 x 10-4 respectively, whereas, for Dithane Z-78, Mancozeb and a combination of Copper ox chloride+ Streptomycin sulphate was 2.6 x 10-4, 8 x 10-5 and 5 x 10-5.respectively. The agrochemicals which were completely inhibitory to the bacterium and did not allow the formation of antibiotic or antibiotic + fungicide resistance mutant were Streptocycline, Streptocycline+ Copper ox chloride and Streptocycline + Bordeaux mixture. Keywords: Antibiotics; Bactericides; Fungicides; Mutant