PHYTOTOXICITY OF AAL-TOXIN AND OTHER COMPOUNDS PRODUCED BY ALTERNARIA-ALTERNATA TO JIMSONWEED (DATURA-STRAMONIUM)

Nine isolates of Alternaria alternata were obtained from infected tomato (cv. Beefsteak) plants. Each isolate was grown on autoclaved rice medium and com meal agar medium and evaluated for pathogenesis and phytotoxicity to jimsonweed plants. Only A. alternata SWSL 1 (NRRL 18822) caused lodging on 1-week-old jimsonweed plants when sprayed at a rate of 20 g of fungus-infested rice per 100 mL distilled water. The symptoms began within 24 to 48 h following inoculation, and all plants were dead after 96 h. Treatment of 2-week-old jimsonweed plants in the same manner affected growth only. No symptoms occurred when SWSL 1 spores from com meal agar were applied to jimsonweed at a rate of 2 x 10(7) spores/mL, with or without dew. The filtrates of fungus-infested rice of the SWSL 1 isolate were found to contain the following phytotoxins: AAL-toxin (100 mug/g), tenuazonic acid (10 mug/g), and alternariol monomethyl ether (580 mug/g). Crude and cell-free filtrates and AAL-toxin (concentration 200 mug/mL) caused similar damage on excised leaves, characterized by soft rot diffusing from the point of inoculation along the veins, adaxially or abaxially to leaves. Alternariol monomethyl ether (concentration 800 mug/mL) and tenuazonic acid (concentration 420 mug/mL) applied to excised jimsonweed leaves caused no visible damage. In intact plants, symptoms resulting from the crude filtrate, cell-free filtrate, and the AAL-toxin were identical. A dose-response study of AAL-toxin on excised jimsonweed and black nightshade (Solanum nigrum L.) leaves showed effects at concentrations of 1.56 mug/mL and 0.01 mug/mL, respectively. This is the first report of phytotoxicity of AAL-toxin to these two weeds and it may have potential as a weed control agent.