Germination ecology and environmental influences on prickly golden fleece (Urospermum picroides) and implications for weed management.

Knowledge of the germination ecology of weed species provides information about their potential aggressiveness and helps develop effective weed management strategies. Therefore, the influence of gibberellic acid (GA) and environmental factors (temperature, light, osmotic stress, salinity, cutting times, and seed burial depth) was evaluated on seed germination and seedling emergence of Urospermum picroides a winter annual weed. The results indicated that maximum seed germination was 94% and 83% when seeds were soaked for 12 and 24 h with 1000 and 800 ppm of GA, respectively. Seed germination was not influenced by light conditions but was influenced by temperature. The highest germination percentages (95% and 93%) occurred at a constant temperature of 30 °C and an alternating temperature of 20/10°C, respectively. In response to light, the results showed that U. picroides is non-photoblastic and can germinate in darkness. Seed germination in response to different cutting times demonstrated that maximum germination was observed in brown achenes (81%), while minimum germination was obtained in white (0%) and yellow (4%) achene stages. Seed germination decreased from 92.5 to 12.5% as water potentials decreased from 0 to -0.4 MPa, and germination was completely inhibited at -0.5 MPa. The salt concentration required for a 50% reduction in maximum germination was estimated at 170 mM NaCl. Maximum seedling emergence occurred at an optimal burial depth of 1.18 cm. In conclusion, this study indicated that at lower soil depths, U. picroides is likely more fit than other species under conditions of low to moderate water and saline stress.