1 Contributions of the Department of Botany, University of Calcutta, Calcutta 700019.
Aqueous extract of leaves of Polygonum orientate L. retarded the germination of test species more than extracts of stem, root and flower of the same plant. In all cases, P. orientale leaf extract adversely affected the seedling growth of mustard and the inhibition was discernible more on the bypocotyl than on the root. Increasing the amount of leaf tissues augmented the inhibitory action and washing removed much of the activity, Phytotoxicity was conspicuous in the extract rather than in the leachate, with the five-day soaked leachate being more potent than ihe three-day one. Successive extractions of the same leaf material showed that the first extract contained most of the active principle (s). Very mature leaves seemed to produce more inhibitor (s) than young and mature leaves. Activity was higher when the bioassay was conducted at 20 or 30 C than at 25 C. Greater toxic effect appeared in the light than in the dark and more during the period ranging from the pre-monsoon to pou-monsoon than during the winter. Extract of dried foliage was less inhibitory than that of fresh foliage, but ash from dry leaves lacked activity. Treatment of aqueous solution of leaves with Norit eliminated much of the inhibitory factor (s) from the solution. The repressing power of the leaf extract was not lost after autoclaving or even after inoculation with a soil micro-organism. The compounds isolated, having inhibitory properties, were possibly luteolin and apigenin glycosides.
