EFFECTS OF ENVIRONMENTAL FACTORS ON SEED GERMINATION AND EMERGENCE OF VELVETLEAF (Abutilon theophrasti)

Velvetleaf. an annual broadleaf weed. is a common and troublesome weed of cropping systems worldwide. Laboratory and field experiments were conducted to determine the effects of environmental factors on germination and emergence of velvetleaf. Seeds germinated over a range of constant temperatures from 10 to 40 degrees C regardless of light conditions, but no germination occurred at temperature below 5 degrees C and beyond 50 degrees C. Seeds germinated at alternating temperature regimes of 15/5 to 40/30 degrees C, with maximum germination (>90%) at alternating temperatures of 40/30 degrees C. Germination was sensitive to water stress, and only 0.4% of the seeds geminated at the osmotic potential of -0.4 MPa. There was no germination at 0.6 MPa. Moreover, germination was reduced by saline and alkaline stresses and no germination occurred at >= 150 mM NaCl or >= 200 mM NaHCO3 concentrations. However, pH values from 5 to 9 had no effect on seed germination. Seedling emergence was significantly affected by burial depth and maximum emergence (78.1-85.6%) occurred at the 1-4 cm depth. The results of this study have contributed to our understanding of the germination and emergence of velvetleaf and should enhance our ability to improve control strategies in cropping systems in central China.