Response of lucerne (Medicago sativa L.) seedlots to different techniques for reducing hard seed content

Various hard seed reduction treatment were applied to machine-dressed (MD) and field-dressed (FD) seedlots of lucerne (Medicago sativa L.) with a high percentage of hard seeds. Mechanical scarification by brushing one through a Huller-scarifier machine (Westrup Type LAH) running at 200 rpm and through tumbling for 10 minutes in a concrete mixer running at 38 rpm increased percentage germination of both MD and FD seedlots, by reducing the hard seed content. In both treatments, the hard seed content was reduced more in MD seedlots than in FD seedlots. Scarifying seeds by sandpapering also increased germination percentage and reduced hard seed content. Stratification treatment (subjecting seeds to an alternating temperature regime of 15 deg C for 16 h/day and 50 deg C for 8 h/day) was also effective. Increasing stratification time increased germination and reduced hard seeds in all seedlots tested. Immersion of hard seeds in all treatments; germination was increased following immersion for 10 and 20 minutes, but for 30 minutes. Long immersion caused the production of a high percentage of abnormal seedlings. Seeds subject to freezing through immersion in liquid air (-195 deg C) had an increased germination and a significant hard seed reduction. However, the percentage of abnormal seedlings increased. Treatment in microwave radiation significantly reduced hard seed content in MD seedlots but only slightly reduced in FD seedlots. MD and FD seedlots were stored for 6 months (12 July 1988 to 12 January 1989) at 5 deg C and in ambient temperature to assess the effect on hard seed content. There was an increased germination and hard seed content in MD seedlots under both storage conditions along with FD seedlots stored in ambient temperature. Storage at 5 deg C for 6 months did not reduce hard seed content in FD seedlots.