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

Nine isolates of Alternaria alternata were obtained from infected toma to (cv. Beefsteak) plants. Each isolate was grown on autoclaved rice m edium and com meal agar medium and evaluated for pathogenesis and phyt otoxicity 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 sympto ms 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) s pores/mL, with or without dew. The filtrates of fungus-infested rice o f the SWSL 1 isolate were found to contain the following phytotoxins: AAL-toxin (100 mug/g), tenuazonic acid (10 mug/g), and alternariol mon omethyl ether (580 mug/g). Crude and cell-free filtrates and AAL-toxin (concentration 200 mug/mL) caused similar damage on excised leaves, c haracterized by soft rot diffusing from the point of inoculation along the veins, adaxially or abaxially to leaves. Alternariol monomethyl e ther (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-f ree filtrate, and the AAL-toxin were identical. A dose-response study of AAL-toxin on excised jimsonweed and black nightshade (Solanum nigru m 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.