Sweetclover Methods
Seed Scarification
Sweetclover seeds can be scarified by rubbing the seeds with fine sandpaper to break the seed coat or by nicking the seed coat with a razor blade. Under the dissecting microscope, hold the seed with one hand while nicking the seed coat with the razor blade held in the other hand. Make the nick in the end of the seed away from the radicle.
An easy method of scarification has been developed by Brigham and Hoover (1956. Agron. J. 48:531-532); the scarifying cup design has been modified by Tom LaRue. For this method, you need to have a stainless steel canister with a detachable stainless steel cap machined. The advantage of stainless steel is that it can be sterilized with bleach and not corrode. The cap is perforated with small holes (diameter ca. 1 mm) to permit air to exit the canister, while keeping the seeds in. The original design had locking pins to close the scarifier, but with most laboratory air pressure lines, it is sufficient to hold the scarifier closed with one hand. There is a central hole in the cap (diameter ca. 6 mm) that serves as an entry port for a connecter which is joined to a vacuum hose. Our scarifying cup has an overall diameter of 5.5 cm and a height of 6.5 cm. The inside is roughened to make certain that the seed coats are broken. In the original design, the inside of the cup was lined with 60-grit emery cloth.
Put the seeds into the canister and cover it. Attach the vacuum hose to the lab air supply. Turn on the air supply for times ranging anywhere from 15 sec to 1.5 min. For example, a time of 15-30 seconds may be sufficient with an air pressure of 25 psi. The seeds will bounce around within the metal cup, and in the process, their seed coats will be broken.
