Dormancy breaking and germination of Alisma plantago-aquatica and Scirpus mucronatus

Various treatments were used to remove seed dormancy of Alisma plantago-aquatica and Scirpus mucronatus, two weeds infesting rice crops. Scarification of A. plantago-aquatica achenes with chloroform or ether and then with 80% sulphuric acid for 5 min gave the highest cumulative germination (c. 80%). Mechanical scarification also stimulated seed germination. These results, plus observations made with an SEM, suggest that A. plantago-aquatica dormancy is exogenous and related to the seed coat characteristics that mechanically constrain the embryo and impede germination. Stratification and vernalisation treatments were used on achenes of S. mucronatus. Chilling treatments increased both germination rate and the number of germinated seeds. The effects of vernalisation and "artificial" stratification on germinability was similar. S. mucronatus appears to possess an endogenous embryo-related dormancy, which is effectively removed by at least a month of achene chilling.