USE OF MIXTURES OF ALLELOCHEMICALS TO COMPARE BIOASSAYS USING RED MAPLE, PIN CHERRY, AND AMERICAN ELM

Toxicity threshold levels for five different bioassays (germination in combination with radicle length, seedling growth, callus growth, plat ing, and cell suspension growth) were determined on three invasive arb orescent species [American elm (Ulmus americana), red maple (Acer rubr um), and pin cherry (Prunus pensylvanica)] using two different mixture s of allelochemicals. Thresholds for the duckweed (Lemna minor) bioass ay and lettuce (Lactuca sativa) seed germination bioassay were also de termined for comparison with the same mixtures. All five bioassays sho wed a sensitivity similar to those of duckweed and lettuce bioassays. The lowest sensitivity was in mixtures containing about 5000 mu g/lite r of each chemical, but the species tested and the mixture applied inf luenced the outcome. Some bioassays could not be used with red maple ( plating and cell suspension) and pin cherry (germination and seedling growth). Cell suspension growth was the most sensitive in in vitro cul ture, whereas callus culture was the least sensitive. Cell suspension growth in multiwell culture plates should be favored in allelopathy st udies because of its sensitivity and the need for relatively small vol umes of sample. Detection of phytotoxicity using whole plant systems ( germination and seedling growth) and tissue culture appeared not to be directly correlated. We conclude that using many bioassays produces t he most conclusive evidence of allelopathic activity.