Effect of environmental factors on wild poinsettia (Euphorbia heterophylla L.) germination- a new introduced weed in soybean field

Wild poinsettia (Euphorbia heterophylla L.) is a summer annual herb, belonging to the Euphorbiaceae family that has recently introduced in Iran and became a troublesome weed in soybean field in Golestan province. Experiments were conducted under laboratory and greenhouse conditions to evaluate the effects of various environmental factors (temperature, light, salinity and drought stress, pH) and planting depth on its germination. The results indicated that seeds germinated at constant temperature range of 15-45 C both in 14 h photoperiod and in darkness. However, germination was greater in the light/dark regime than in darkness, as maximum germination percentage (83%) and germination rate (11.34 seed day-1) was observed at 35 C with the 14 h photoperiod. At alternating day/night temperatures, the highest germination percentage (95%) and germination rate (12.99 seed day-1) occurred at 40/30 C. Germination was reduced with increasing draught stress and no germination was observed at -1.0 MPa. Wild poinsettia seeds germinated >80% at salt concentrations of 0-40 mM. Germination declined with increasing salinity stress. Germination was 13% at salt concentrations of 160 mM. Germination was not affected by pH levels. Maximum emergence was (88-95%) when seeds were sown at 0.2-3 cm depth in soil, with no emergence occurring at a planting depth of 6 cm. It is concluded that several environmental factors affecting the germination of wild poinsettia, and this information could help to predict the spread of wild poinsettia in new areas.