Effects of Environmental Factors on Germination and Emergence of Swallowwort

Swallowwort, a twining perennial of the Asclepiadaceae family, has become increasingly invasive in cultivated fields, orchards, fence rows, natural areas, and roadsides of some provinces in Iran. The ability of this weed to establish and develop from seed was studied in laboratory and greenhouse experiments. Optimum germination temperature was 25 C. Germination did not occur at ≤ 15 C either in dark or light. In temperature fluctuation experiments, maximum germination occurred at 30/22 C, but light fluctuations had no effect on swallowwort seed germination. At pH 4 to 9 seed germination was 44 to 66%. Osmotic potential up to −0.2 MPa had little effect on germination. Seed germination was less than 5% at −0.8 Mpa. Swallowwort seeds were not able to germinate at 300 mM NaCl; however, there was 12% germination at the 200 mM concentration. Maximum emergence occurred when the seeds were planted at 1.5 cm depth. Seedlings did not emerge when planted at 6.5 cm depth. Germination percentage of the seeds kept under immersed (water) conditions was similar to those of nonimmersing periods; however, seedling growth was greater in treatments without immersing periods.Nomenclature: Swallowwort, Cynanchum acutum L.