Optimization of screening of native and naturalized plants from Minnesota for antimicrobial activity

The White Earth Tribe of Ojibwe and the University of Minnesota have partnered to identify antimicrobial properties in native plant species in the Upper Mississippi River and Red River Basins. Optimization of harvest time, tissue preparation, and extracting solvent methods was completed using extracts from two species with known antimicrobial activity, Betula papyriferaand Rhus typhina. Tissue was collected at three different times (July, August, and September) corresponding to different developmental states (juvenile, reproductive, post-reproductive) and extracts were prepared from fresh, frozen, or dried tissue using one of three solvents, acetone, ethanol, or methanol. Using optimized methods plant extracts from 265 above ground plant components (flower, leaves, stems, berries) of 130 species were tested against four microorganisms (Escherichia coli, Pseudomonas aeruginosa, Candida albicans,Staphylococcus aureus). Eighty extracts were found to inhibit at least one microorganism. Sixteen extracts inhibited two microorganisms, six extracts inhibited three microorganisms, and three extracts inhibited all four microorganisms. Extracts from R. typhina and B. papyrifera leaves were also tested against soil borne pathogens, Fusarium solani, Phytophthora sojae, Rhizoctonia solani, and Pythium spp, in order to assess potential uses as seed protectants. Rhus spp extracts inhibited F. solani and Pythium spp as well as a commercial fungicide seed treatment applied as a control. Key words: Antimicrobial, native plants, antifungal seed treatment.