Germination of bur buttercup seeds.
Bur buttercup (Ranunculus testiculatus) is an annual weed that has spread rapidly through range and crop lands in western USA. It contains the toxic substance ranunculin and has been a particular problem in winter wheat fields. Germination experiments in the laboratory indicated that about 30% of the achenes germinated without pretreatment, but only at cool to cold temp. (max. germination at 28°C). Acid scarification for 25 min. enhanced germination, which was further stimulated by the addition of 0.289 mmol gibberellic acid/litre and 0.01 mol potassium nitrate/litre. Achenes treated in this way and incubated at constant or alternating temp. of 0-40°C gave a germination percentage of up to 70%. Germination was generally highest at cool temp., values >30°C greatly suppressing or inhibiting germination. At cool to cold temp., embryos dissected from the achene coats showed 60% germination without additional pretreatment. About 30% of the achenes appeared to be adapted for germination at cold seedbed temp., reflecting the pattern found for plants with ephemeral growth habits.