Effect of Ecological Factors on Seed Germination of Alien Weed Tridax procumbens (Asteraceae)

Aims: To determine the effects of light, temperature, pH, salt stress, moisture content, depth of seed burial, and storage periods on its seed germination of Tridax procumbens seeds.
Study Design: The seeds of T. procumbens were collected in October - December 2012 from several paddy fields along Thailand. Seeds collected from many randomly selected plants were unsoiled and stored at room temperature until used in the experiments.
Place and Duration of Study: The experiment was conducted in Faculty of Science and Technology, Phranakhon Rajabhat University, between January 2013 and May 2014.
Methodology: To increase understanding of its rapid spread, the influences of light, temperature, pH, salt stress, moisture content, depth of seed burial, and storage periods on its seed germination have been evaluated.
Results: The seeds were obviously stimulated germination by light in T. procumbens, with highest germination rate at an alternating under the 12 h light/12 h dark regime, but a few seeds still germinated in the dark. The seeds germinated at a constant temperature in the range of 5–45ºC and reached a maximum at 25ºC. The seeds germinated over a wide pH range (4–10), with the highest germination rate at 7. The optimum soil moisture content for germination was around 5- 40%. The species was moderately tolerant of salt stress, with NaCl solution concentration > 0.15 mol L-1. The highest seedling emergence occurred for seeds placed from 0 to 2 cm deep, and no seedlings emerged from a 3-cm burial depth. The seeds of T. procumbens have no apparent dormancy and retain a high viability after room storage for 450 days.
Conclusion: This study has demonstrated that T. procumbens are adapted to a wide range of environmental conditions.