A Comparison of Seed Germination Ability between Exotic and Indigenous Weeds in Taiwan

Abstract

The influence of environmental factors on seed germination ability between five exotic weeds, i.e., floss flower (Ageratum houstonianum Mill.), celosia (Celosia argentea L.), mile-a-minute (Mikania micrantha Kunth), beggarticks (Bidens pilosa L.) and passionflower (corkystemmed)(Passiflora suberose L.), and an indigenous weed flatsedge (Cyperus iria L.) in Taiwan was evaluated. While seeds of all six species germinated at temperatures between 20 and 36 C with the optimum for passionflower falling between 24 and 32 C, seeds of the two Compositae spp., floss flower and beggarticks, preferred lower temperature, with declining germination rate at increasing temperature. The germination of five weeds was inhibited with osmotic potentials increasing from -0.4 to -1.0 MPa, but that of passionflower was not affected by osmotic potential up to -1.0 MPa. Seed germination of all five exotic weeds was not altered much when pH of the moisture supply varied between 4.0 and 9.0, in contrast, that of the indigenous flatsedge was significantly reduced to 30% with pH increasing from 8.0 to 9.0. Although the seed germination of floss flower, mile-a-minute, beggarticks and flatsedge was light-dependent, that of celosia and passionflower was only slightly inhibited in dark. Under the climate conditions and soil environments in Taiwan, the five exotic weeds tested, especially passionflower, are expected to display higher seed germination ability than the indigenous weeds. Therefore, the invasion risk of exotic weeds should be closely monitored in both the field and non-farming lands.