The influence of environmental factors on seed germination of Xanthium strumarium L.: Implications for management

Xanthium strumarium L. (Common cocklebur) is a noxious weed prevailing in different ecosystems around the world. It incurs significant yield and economic losses in different cropping systems globally. Successful management of any weed species depends on sound knowledge of seed germination biology. However, detailed knowledge on seed germination biology of the species is missing. Therefore, we investigated the impact of different environmental factors on seed germination and seed burial depths on seedling emergence of two X. strumarium populations. The impact of different sorghum mulch doses (0-10 t ha(-1)) on seedling emergence of the tested populations was also explored. Seed germination was evaluated under different photoperiods (0, 12 and 24), constant temperatures (0-50 degrees C with 5 degrees C stepwise rise), and different levels of pH (3-12), salinity (0-600 mM) and osmotic potential (0 to -1.6 MPa). Seedling emergence was observed for seeds buried at different depths (0-15 cm). Seeds of both populations proved non-photoblastic; however, higher germination was recorded under 12-hour photoperiod. The seeds germinated under a wide range of constant temperatures (10-45 degrees C), pH (4-10), osmotic potentials (0 to -0.8 MPa) and salinity levels (0-400 mM NaCl). However, the highest germination was observed under 30-31 degrees C temperature and neutral pH (7.51-7.52). Seeds were able to withstand 400 mM salinity and -1.00 MPa osmotic potential. Seedling emergence was initially improved with increasing burial depth and then a sharp decline was noted for the seeds buried >3 cm depth. Most of the seeds of both populations did not emerge from >8 cm depth. Different sorghum mulch doses linearly suppressed seedling emergence of tested populations, and 5.83-5.89 t ha(-1) mulch application suppressed 50% of seedling emergence. Seedling emergence was completely retarded with 8 t ha(-1) sorghum mulch. The tested populations germinated under diverse environmental circumstances indicating that the species can become troublesome in marginal habitats and cropped lands. Deep burial of seeds and application of sorghum mulches suppressed seedling emergence. Thus, deep burial followed by shallow tillage and application of sorghum mulches could be used as a successful strategy to manage the species in agricultural fields. Nonetheless, management strategies must be developed to control the species in other habitats.