Physiological Basis of Achene Dormancy in Polygonum convolvulus (Polygonaceae)

Abstract

Germination of dormant achenes of wild buckwheat (Polygonum convolvulus L.) was promoted at 25 C if they were stratified at low temperatures. Preincubation at either 2 C or 10 C promoted subsequent germination at 25 C equally, although the period of time to reach maximum germination was shorter for the 2 C treatment. Moreover, a preincubation treatment of a daily alternating cycle 2 C for 20 hr and 10 C for 4 hr promoted germination at 25 C more than either temperature alone. Removing portions of the hard pericarp and testa did not promote germination of dormant achenes at 25 C except when the portion of those structures covering the tip of the radicle was removed. This suggests that the structures covering the embryo do not prevent germination by restricting the movement of water or gases but rather restrict growth mechanically. Complete removal of the pericarp promoted germination, but much higher germination was obtained when the testa was also removed, indicating that the pericarp may not be the main factor in dormancy. Thus the role of low temperature in the loss of dormancy in wild buckwheat achenes may be to promote the production of hydrolytic enzymes that lower the mechanical resistance of pericarp and testa and/or increase the embryo growth potential beyond some threshold level and thereby enable the radicle to overcome the resistance to growth imposed by the structures covering the embryo.