Allelopathic effects ofEupatorium riparium on population regulation of two species ofGalinsoga and soil microbes

Summary Allelopathic effect ofEupatorium riparium Regel, a dominant ruderal weed at higher altitudes in Meghalaya state in north-eastern India, was studied on two common sympatric annual weeds,Galinsoga ciliata (Raf.) andG. parviflora Cav. and on soil microbes. Seed germination and radicle and plumule growth of both species ofGalinsoga were suppressed by the aqueous extract and leachate ofE. riparium. Although the leaf leachate, leaf and litter extracts and litter bed caused considerable reduction in leaf area and seed and dry matter production in both species ofGalinsoga, the effect was much more pronounced onG. parviflora. The inhibitory effect was directly correlated with the concentration of the extract and leachate. The soil microbial population and growth of theGalinsoga spp. declined considerably in the experimental pots where the soil had earlier received leachate of different plant parts ofE. riparium growing in it. The presence of the partly decomposed litter ofE. riparium in the pots reduced soil microbial population and growth of the two weeds much more strongly as compared to the litter in the advanced stages of decomposition. The study also revealed that the abundance and colony growth of the two test fungiviz. Trichoderma viride andAspergillus flavus were differentially affected by the allelopathy ofE. riparium; T. viride being favoured andA. flavus inhibited.