Use of Mixtures of Allelochemicals to Compare Bioassays Using Red Maple, Pin Cherry, and American Elm

Abstract

Toxicity threshold levels for five different bioassays (germination in combination with radicle length, seedling growth, callus growth, plating, and cell suspension growth) were determined on three invasive arborescent species [American elm (Ulmus americana), red maple (Acer rubrum), and pin cherry (Prunus pensylvanica)] using two different mixtures of allelochemicals. Thresholds for the duckweed (Lemna minor) bioassay and lettuce (Lactuca sativa) seed germination bioassay were also determined for comparison with the same mixtures. All five bioassays showed a sensitivity similar to those of duckweed and lettuce bioassays. The lowest sensitivity was in mixtures containing about 5000 μg/liter of each chemical, but the species tested and the mixture applied influenced 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 culture, whereas callus culture was the least sensitive. Cell suspension growth in multiwell culture plates should be favored in allelopathy studies because of its sensitivity and the need for relatively small volumes 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 the most conclusive evidence of allelopathic activity.