Antibacterial Activity of Plant Extracts against Bacterial Pathogens of Tomato

Tomato plants of all ages are susceptible to Clavibacter michiganensis subsp. michiganensis, Xanthomonas sp. and Pseudomonas syringae pv. tomato. Control is based mainly on copper-containing chemicalsand is often unsatisfactory. The object of this study was to test the effect of extracts from different, common for Bulgaria, medicinal and weed plants against referent strainsin vitro. Fresh plant aerial parts were oven-dried or freezed before extraction. Methanol and nhexane were used as solvents. Extractions were prepared in Soxhlet extractor at 80С/4h. Methanol and hexane were recovered in a vacuum evaporator. The fractions were diluted in water (%, w/v) with dimethylsulfoxide as dilution agent for some extracts. The in vitro test was completed by the agar diffusion method in triplicate with 50µl of each substance. The antimicrobial activity was assessed by measuring the diameter of the inhibition zone. A total of 25 plants and 47 methanol and n-hexane extracts were tested against the pathogenic bacteria of tomato. Extracts from seven plants have potential to be used against C. michiganensis subsp. michiganensis. Methanol extract from C. majus has the biggest potential for control of Xanthomonas of tomato and also has some effect against C. michiganensis subsp. michiganensis. H. spectabile has the potential to control all four bacteria but higher concentrations need to be tested. Methanol extract from Chaenomeles sp. has a good potential for control of all pathogens in concentrations of 5%.