ALLELOPATHIC POTENTIAL OF Phormidium angustissimum

In a laboratory bioassay, the allelopathic effects of Phormidium angustissimum were investigated on seed germination, shoot length and root length of Chinese amaranth (Amaranthus tricolor L.) and barnyard grass (Echinochloa crus-galli [L] P. Beauv.). The seeds were germinated in Petri dishes with aqueous extract (1.25 to 10% concentrations) and crude organic extracts (500 to 4000 ppm concentrations) with distilled water used as control. The inhibitory effect on these test plants was directly proportional to the increasing concentration of aqueous extracts of P. angustissimum. At the highest concentration studied, the aqueous extract completely inhibited the germination of Chinese amaranth. In barnyard grass, the aqueous extract had a moderate effect on seed germination and seedling growth. To investigate the allelochemicals, P. angustissimum was extracted with organic solvents, hexane, ethyl acetate and methanol. The crude ethyl acetate was most inhibitory to Chinese amaranth, but all three crude organic extracts had lowinhibitory effect on barnyard grass. Bioactivity guided extraction and chromatographic techniques were used to isolate and purify the allelochemicals from the crude ethyl acetate extract of P. angustissimum. The pure compoundswerestudied by extensive GC-MS and NMR spectroscopic methods in order to determine their structures. The crude ethyl acetate extract of P. angustissimum yielded C11 norisoprenoid, dihydroactinidiolide and a mixture of long chain fatty acids. Dihydroactinidiolide displayed the highest inhibitory activity against seed germination and seedling growth of Chinese amaranth and barnyard grass.