Seed extracts impede germination in Brassica rapa plants

Allelopathy is an important mechanism of interference competition in some plants, but little is known about whether compounds exuded from seeds influence the germination of neighbors. We treated seeds of multiple lines of Brassica rapa (field mustard) with aqueous extracts of Brassica rapa Fast Plant seeds and extracts of seeds of the invasive, allelopathic plant Alliaria petiolata (garlic mustard). Germination patterns differed significantly among populations, with Fast Plants germinating earliest. As predicted, Alliaria seed extracts significantly delayed germination compared to controls. Surprisingly, Fast Plant extracts reduced germination probability and delayed germination more than both controls and Alliaria extract-treated seeds. These results suggest that compounds in the seeds of both species appear to be allelopathic, and indicate a potentially important and unrecognized role for allelopathy in intra- and inter- specific competition at the seed stage.