ALLELOPATHIC EFFECTS OF LIVING QUACKGRASS (AGROPYRON-REPENS L) - IDENTIFICATION OF INHIBITORY ALLELOCHEMICALS EXUDED FROM RHIZOME BORNE ROOTS

A root exudate recirculating system was used to study effects of estab lished Agropyron repens (quackgrass) plants, grown from rhizome pieces , on cress seedlings as the acceptor plants. The biomass and shoot len gth of the cress seedlings was significantly reduced when quackgrass p lants were 54 days old, indicating that rhizome borne roots of living quackgrass exude phytotoxic compounds. This effect was diminished with increasing age of the donor plants. The constituents of root exudates of quackgrass were analyzed and the compounds identified. Besides DIB OA, whose concentration dropped with increasing age of the donor plant s, beta-hydroxybutyric-, 4-hydroxycinnamic-, ferulic-, vanillic-, syri ngic-protocatechuic acid and vanillin were found. Two of the compounds , DIBOA and ferulic acid were tested for their effects on Lepidium sat ivum, Amaranthus retroflexus, Brassica napus, Lolium perenne, Poa annu a, Hordeum vulgare, Secale cereale, and Triticum aestivum radical grow th. Generally, ferulic acid was less effective than DIBOA. A species a nd dose dependent response of the tested plants was observed. Very low concentrations were without effect or slightly stimulatory, whereas h igher ones resulted in growth inhibition. Dicot species were more sens itive than monocots. Hydroxamic acid containing cereals were affected only at the highest concentration used.