Antibacterial activity of Alternanthera philoxeroides (Mart.) Griseb. against bacterial phytopathogens: Erwinia carotovora, Ralstonia solanacearum and Xanthomonas axonopodis

We investigated the antibacterial activity of alligator weed (Alternanthera philoxeroides) organic extracts against three bacterial phytopathogens (Erwinia carotovora, Ralstonia solanacearum and Xanthomonas axonopodis). The extracts were prepared by soaking the dry powder of leaf, stem and root of A. philoxeroides into methanol, n-hexane, chloroform and ethyl acetate. The disk diffusion method was used to determine the antibacterial activity at 100 mg/mL extract concentration. The n-hexane extract of A. philoxeroides leaves showed the maximum inhibition zone diameter (IZD) = 28.1 mm against R. solanacearum, while, the corresponding value for the positive control (Penicillin) was 48 mm IZD. There was no antibacterial activity of negative control, dimethyl sulfoxide (DMSO). Gas Chromatography Mass-Spectrometry (GC-MS) analysis revealed the presence of acetic acid, 2-(2-methoxycarbonylamino-5-nitrophenylthio)-, methyl ester, at the highest concentration (31.9 %), followed by 1, 4-benzenediol, 2, 5-bis (1,1-dimethylethyl)- (15.06 %),. It was concluded that the observed biological activity in this study may be due to the presence of these compounds.