Germination of bur buttercup seeds.

Abstract

Bur buttercup (Ranunculus testiculatus Crantz) is an alien annual species that has spread rapidly through range and croplands in the western United States. This species is potentially poisonous and is currently a weed in cereal grain fields. We investigated the germination of the achenes (seeds). About 30% of the seeds of bur buttercup germinated without pretreatment, but only at cool to cold temperatures (maximum germination 28% at 5 degrees C). Germination was not enhanced by light, washing, or prechilling of seeds. Acid scarification for 25 minutes increased germination. Enrichment of the germination substrate with 0.289 mmol L-1 gibberellic acid (GA(3)) and 0.01 mol L-1 potassium nitrate (KNO3) synergistically enhanced the germination of acid scarified seeds. Incubation of seeds pretreated in this manner at 55 constant or alternating temperatures resulted in maximum germination of 70%. All temperature regimes with optimum germination (defined as not lower than the maximum observed and one-half its confidence interval at 0.01 level of probability) occurred at relatively cool temperatures. Temperatures above 30 degrees C greatly suppressed or inhibited germination. Embryonic plants dissected from the achene costs had 60% germination without additional pretreatment, but only at cool to cold incubation temperatures. The germination-dormancy requirements of bur buttercup seeds are obviously complex, but about 30% of the seeds appear adapted for germination at cold seedbed temperatures, which fits with the extreme ephemeral growth habit of the species.