Dormancy breaking in Digitaria sanguinalis seeds: the role of the caryopsis covering structures

After shedding, most propagules of large crabgrass (Digitaria sanguinalis (L.) Scop.) are dormant. The objective of this study was to test several dormancy-breaking treatments in D. sanguinalis spikelets (dispersal units). The methods evaluated were: (1) pre-soaking in water, (2) chemical scarification, (3) rubbing with sand. (4) surgical cuts in the seed covering structures, and (5) removal of covering structures. All germination trials were carried out with two-month-old spikelets at 20 degrees C (12h darkness)/30 degrees C (12h light). The mean germination percentage of intact spikelets was 4%. Removal of the glumes and the lemma of the sterile floret increased the percentage to 19%. If the lemma of the perfect floret was also removed germination reached 80%. Nevertheless, the most successful dormancy-breaking treatment was to dehull the caryopses using emery paper (>95%). These results indicated that dormancy is caused mainly by the caryopsis covering structures, especially the lemma of the perfect floret. However, the caryopsis coal was also noted to have an effect. Chemical scarification did not significantly increase the germination of intact spikelets. In contrast, pre-soaking spikelets in water for four days increased then cumulative germination by 20% The weakening of coverings by rubbing spikelets with moist sand stimulated spikelet germination to near 30%.