With increasing concerns of the environmental problems associated with current fungicide application, investigation of alternative, environmentally compatible biopesticides for plant disease management is needed. A total of 113 strains associated with Acanthus ilicifolius Linn in the Maipo Reserve, Hong Kong, were isolated and identified. In vitro assay with crude extracts of bacterial fermentation cultures identified ∼26% of the isolates producing antimicrobial compounds against a variety of agriculturally important phytopathogens. Selected crude extracts with inhibition to Colletotrichum fructicola and Magnaporthe oryzae growth significantly suppressed anthracnose and rice blast development in pear fruits and rice plants, respectively, when applied at 50 μg ml-1. Furthermore, 10 of 14 selected crude extracts with good antimicrobial activities had no significant differences in toxicity to the genus Chlorella compared with the control when used at 25 μg ml-1, whereas Amistar Top and Mancozeb completely killed the alga under the same concentration. These data illustrate the potential of natural products from mangrove rhizosphere bacteria in future agricultural application.
Keywords: cereals and grains; field crops; fungi; prokaryotes; vegetables.