Effects of Environmental Factors on Germination and Emergence of Siam Weed (Chromolaena odorata)

Abstract

Abstract Laboratory and greenhouse studies were conducted to determine the effect of several environmental factors on seed germination and seedling emergence of Siam weed (Chromolaena odorata). Seeds germinated over a range of 10 to 35 with optimum germination at 25. Low temperature markedly restricted germination, with no germination occurring at 5. Siam weed was moderately photoblastic, with 38% germination occurring in the dark. Germination decreased with increasing water potential, and germination was totally inhibited at osmotic stress higher than -0.8 MPa. Germination was greater than 65% at less than 50 mM NaCl and greater than 20% at 200 mM NaCl, with no germination at 300 mM NaCl. Maximum emergence occurred when seeds were planted on the soil surface. No seedlings emerged when planted 3.5 cm deep. These results suggest that the future range of Siam weed in China will be restricted largely to the Southern China.