PHYTOTOXIC SUBSTANCES IN TWELVE SUBTROPICAL GRASSES

Aqueous extracts of 12 subtropical grasses inhibited seed germination and radicle growth of Lactuca sativa var. Great Lakes at osmotic concentrations as low as 10 milliosmol. Acroceras macrum, Chloris gayana, Digitaria decumbens, and Panicum maximum exhibited the highest inhibition, while Cortaderia selloana revealed the least. Toxic spots were found on chromatograms of the ether fraction of aqueous extracts. Cynodon dactylon, Setaria sphacelata, and Tripsacum laxum showed more than six toxic spots, while Andropogon nodosum, Bracharia mutica, and Chloris gayana gave less than three toxic spots. The phytotoxins fexulic, syringic, p-coumaric, vanillic, p-hydroxybenzoic, and o-hydroxyphenylacvtic acids were identified. These compounds are differentially distributed in the 12 grasses studied. Additionally, most of these compounds were also found in the associated Soils; the control (nonherb-growth) soil provided the toxic compounds in significahtly loss amount than did the grass soils.