Antibacterial activity against Xanthomonas campestris pv. vitians and Pseudomonas cichorii of different plant extracts prepared from horticultural and forest species
Different aqueous-ethanolic extracts prepared from wastes of horticultural and forest species were tested in vitro for their antibacterial activity against Xanthomonas campestris pv. vitians and Pseudomonas cichorii causing bacterial leaf spot and varnish spot of lettuce, respectively. Among the 17 horticultural extracts, 13 show minimum bactericidal concentrations (MBCs) ≥ 50 mg ml-1 against X. campestris pv. vitians and P. cichorii. On the other hand, three of the 20 forest extracts show MBCs ≥ 50 mg ml-1 against both bacteria. Low MBCs (≤ 6.25 mg ml-1) against both bacteria were obtained with extract #3 from cranberry fruit, fruit extract from grey alder, bark extract from red oak, bark extract from red maple, and twig extract from balsam fir. Results obtained show that antibacterial activity varies according to species and structure used to prepare the extract; extracts from forest species exhibit stronger antibacterial activity. Antibacterial activity can also vary from batch to batch of a same extract. The extracts with strong antibacterial activity (MBC ≤ 6.25 mg ml-1) will be further investigated for their efficacy to repress the development of X. campestris pv. vitians and P. cichorii populations on lettuce plants and to control bacterial leaf spot and varnish spot.