Cultivar and storage effects on germination and hard seed content of alfalfa

Abstract

The impermeable coat of alfalfa (Medicago sativa L.) seed can reduce germination to an extent unacceptable for commercial use. The usual method of increasing germination of lots with high proportion of impermeable or hard seeds, mechanical scarification, can damage seeds. Experiments were conducted to determine the effect of cultivar, year of production and storage conditions on germination and hard seed content in alfalfa. Experiments with four Canadian cultivars indicated a significant effect of cultivar on seed weight, germination and hard seed content in freshly harvested seed. Year of production had a greater influence on these seed traits than cultivar. Under uncontrolled storage conditions, germination of 35 alfalfa synthetics increased and hard seed content decreased with time, although not at the same rate for all synthetics. Storage at 20 °C for up to 64 mo did not significantly decrease hard seed content. At 35 °C, hard seed content decreased continuously for all cultivars (for one cultivar to <5%) after 64 mo. Over 80.5 mo storage at room temperature (22 ± 2 °C), germination increased in a nonlinear fashion. Storing seed in sealed plastic bags at 35 °C delayed seed dehydration and the loss of hard seeds. Levels of nonviable seed were low (<10%), even after storage at 35 °C for 64 mo. Brief (1 min) exposure to liquid nitrogen increased germination of freshly harvested alfalfa seed to >90%. The results indicate that the germination percent of alfalfa can be increased and hard seed content reduced by short exposure to liquid nitrogen or storage at nonlethal high temperatures (35 °C) such that mechanical scarification may be unnecessary. Key words: Medicago sativa, hard seed, stored seed, seed dehydration, high temperature treatment, liquid nitrogen treatment