Seed germination and dormancy of Sida rhombifolia L

The effects of seed scarification, temperature, light, salt, osmotic stress, and pH on seed germination, as well as the impacts of seed burial depth on Sida rhombifolia seedling emergence, were assessed by experiments. Sulfuric acid scarification caused seeds to come out of dormancy and accelerated germination; however, light had no effect on the germination of scarified seeds. Compared to non-scarified seeds, which germinated at a rate of 5%, seeds treated with sulfuric acid for 120 minutes produced 65% of the seeds. The response to scarification indicates that a hard seed coat is the primary mechanism restricting germination. In two separate experiments, a concentration of 111 mM sodium chloride and an osmotic potential of -0.49 MPa reduced maximum germination (64 to 65%) of S. rhombifolia by 50%. Germination was not influenced by the pH of buffered solutions ranging from 5 to 9, and it varied from 60 to 65% over this range. Seedling emergence was greater than 60% at burial depths of 0.5 to 2 cm, but decreased thereafter, and and no seedlings emerged from the seeds buried at 8 cm. The results of this study identify some of the factors enabling S. rhombifolia to be a widespread and problematic weed in the humid tropics and provide information that may contribute to its control.