GERMINATION ECOPHYSIOLOGY OF BUR BEGGARTICKS (BIDENS TRIPARTITA) AS AFFECTED BY LIGHT AND OXYGEN

Laboratory experiments were conducted to determine the effect of light , oxygen, and submergence on bur beggarticks seed germination. Fresh a nd dry stored seeds exhibited dormancy, requiring thiourea and light f or germination. Red light was more effective than far-red or blue ligh t in breaking dormancy. Both an oxygen-saturated and anoxic atmosphere completely inhibit ed germination. Hypoxic conditions (5 and 10% oxyg en) led to an increase in germination compared to normoxia (21% oxygen ). Primary dormancy was eliminated by 1 yr of soil burial. Seeds exhum ed after soil burial had greater germination percentage than fresh or lab-stored seeds after a brief far-rad irradiation, bur did not germin ate in tile dark. The induction of secondary dormancy increased with i ncreasing durations of submergence. Finally, sowing at different soil depths (0 to 8 cm) showed that germination and emergence occurred main ly with shallow burial (0.5 to 1.0 cm).