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

Abstract

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 (GA₃) 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 GA₃, 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.

Keywords: Burial depth; Cutting time; Growth hormone; Osmotic potential; Salinity.

Fig. 1

Effect of gibberellic acid (GA₃) on seed germination of Urospermum picroides at 12 and 24 h seed soaking times. Vertical bars represent the mean standard error.

Fig. 2

Effect of constant temperatures (light/dark) on seed germination of Urospermun picroides. Vertical bars represent the standard error of the mean.

Fig. 3

Effect of cutting time on seed germination of Urospermum picroides. Vertical bars represent the mean standard error.

Fig. 4

Seed maturation stages of Urospermum picroides: Closed capitule with white achene (A), closed capitule with yellow achene (B), closed capitule with greenish-brown achene (C), closed capitule with brown achene (D) and open capitule with brown achene (E).

Fig. 5

Effect of osmotic potentials on germination of Urospermum picroides. Vertical bars represent the mean standard error.

Fig. 6

Effect of NaCl concentration on germination of Urospermum picroides. Vertical bars represent the mean standard error.

Fig. 7

Effect of seed burial depth in the soil on seedling emergence of Urospermum picroides 21 days after sowing. Vertical bars represent the mean standard error.