This study was carried out to evaluate the antibacterial activity of clove (Eugenia caryophylata) hexane extract, cinnamon (Cinnamomum zelanicum), and datura (Datura metel) ethanol extracts against the phytopathogenic Erwinia carotovora subsp. atrosepticagrowth, causative agent of black stem and soft rot on potato, in both cultured media and on plants in pots under natural conditions. Concentrations of 0.2, 0.5, 1, 3 and 5% of each extract were subjected for preliminary antibacterial assays against E. carotovora subsp.atroseptica in nutrient agar by pour plate method. The results of in vitro antibacterial activity showed that hexane extract (essential oil) of clove at 0.2% exhibits the highest inhibitory effect against the pathogenic bacteria, 100% compared to 80 and 90% with ethanol extracts of cinnamon and datura at the same concentration. The complete inhibition of E. carotovorasubsp. atroseptica growth by cinnamon and datura extracts was achieved at 0.5% concentration. Similar results of the antibacterial activity of the extracts on E. carotovorasubsp. atroseptica, on the plant in the pots under natural conditions, were obtained. The greatest suppression of potato black stem and soft rot disease was obtained on plants grown from extract-treated tubers sown in bacteria contaminated soil as well as on plants grown from bacteria-contaminated tubers sown in extract-treated soil (zero infection), compared with untreated tubers in contaminated soil, or contaminated tuber in untreated soil. The application of extracts on potato plant foliage grown from bacteria-contaminated tubers or in bacteria-contaminated soil had no effect on disease incidence, but the application of the extracts on the foliage before bacterial contamination highly inhibited the disease incidence.
Key words: Antibacterial, clove, cinnamon, datura, Erwinia carotovora, black stem, soft rot, potato disease, plant extracts.
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