Baseline information on inducing germination of dormant leafy spurge seeds with growth regulators and chemicals is lacking. This study was conducted to survey the effect of various substances on germination of leafy spurge seeds. The nontreated control seeds in this population were nearly fully imbibed in 3 h and displayed approximately 35% germination in 21 d under the normal alternating temperature of 20/30 C (16/8 h). Gibberellic acid (GA₃, 10 mM) induced 65% germination at constant temperatures of 20 and 30 C. The alternating temperature increased the effectiveness of 10 mM GA₃ with 94% germination, a twofold increase over the control. Nontreated seeds did not germinate at the constant temperatures, suggesting that alternating temperature acts via a GA-independent pathway. Kinetin at 0.1 to 1 mM was no more effective than the control, but a saturated solution of kinetin induced 73% germination. Ethephon at 0.01 to 1 mM induced 58 to 66% germination, although there was little response to different concentrations. Ethylene gas at 1 ppm stimulated germination to 77%, a 1.8-fold increase over the control. Germination of seeds incubated continuously in 1 and 10 mM nitrate displayed 35 and 40% germination, respectively. Seeds pulsed for 24 h with 100 mM nitrate displayed 58% germination after 21 d. Potassium phosphate–citrate buffer (pH 3.4) and its individual components induced 60 to 70% germination. Fluridone (10 and 100 µM), 1-naphthaleneacetic acid (NAA, 0.1 to 10 mM), and ethanol (0.2 to 15%) had no effect on germination, but subsequent elongation in the presence of NAA was inhibited because of swelling of the radicle. This research reveals that GA₃ is the most effective growth regulator for germination of dormant leafy spurge seeds, and its effect is independent of temperature.

Nomenclature: Leafy spurge, Euphorbia esula L. EPHES.