The Effect of High Temperature Contact Treatment on Hard Seeds in Alfalfa

The presence of “hard seeds” or seeds which are covered with an impermeable seed coat has long been the topic of much study and interest in the processing, sale, and use of legume seeds. Hard seeds are seeds which fail to germinate or take up water when subjected to moisture and temperature conditions which are favorable to germination. These seeds are inherently viable and are capable of producing normal seedlings but do not initiate growth as rapidly as normal seeds. Hard seed content of samples of seed may be extremely variable and is often an important factor in determining the commercial value of any lot of legume seed. Lots of seed which contain an extremely large percentage of hard seed often meet with much disfavor in the eyes of those who wish to purchase the seed for planting. The difficulty of selling seed with high percentage of hard seeds and the reduced sale value of such seed has led to many attempts to devise a seed treatment which will overcome this undesirable quality. Proper seed treatment methods should render seed coasts of hard seeds permeable to water so they will produce normal growth in the seven days commonly allowed for the germination test. Many seed treatments effectively decrease hard seed content but either are not applicable for use with large amounts of seed or cause an undesirable increase in percentages of dead seeds and abnormal seedlings. The object of this study was to devise a method of seed treatment which might reduce the hard seed content of legume seeds by use of surface contact with high temperature. This method theoretically should cause slight burning of a small area of the seed cost without causing any damage to the embryo or the cotyledons. Surface heat would not increase the internal temperature of the seed to any large degree but should be able to increase seed coat permeability. It was hoped that a treatment might be devised which could be used in all legumes to decrease hard seed content with a corresponding increase in germination