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Germination of Forage Crop Seeds After 20 Years of Subfreezing Storage¹

There is little literature on the effect of long-term subfreezing storage of forage crop seeds. Furthermore, most seed storage studies include only one or two samples of a given kind of seed. In this study germination percentages for 260 forage crop seed lots were determined after 20 years of subfreezing storage. The study included alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), white clover (T. repens L.), alsike clover (T. hybridum L.), birdsfoot trefoil (Lotus corniculatus L.), smooth bromegrass (Bromus inermis Leyss.), orchardgrass (Dactylis glomerata L.), timothy (Phleum pratense L.), and perennial ryegrass (Lolium perenne L.) Seed from 26 cultivars of nine species produced at three locations (Prosser, Wash., Shafter and Tehachapi, Calif.) in 1961, was placed in cotton bags in a freezer at –15 C and 60% relative humidity soon after cleaning in the year of harvest. Each seed lot was tested for germination in 1961 and retested in 1981. Red clover, bromegrass, orchardgrass, and timothy retained germinability for 20 years in this study in sharp contrast to the significant losses in a previous study. Continuous subfreezing storage conditions in this study, as opposed to most seed lots in the earlier study being stored 1 to 2 years at 5 C before being placed in subfreezing storage, may account for these differences. Location of seed production was not important except for significant losses in germination of alfalfa seed produced at the two California locations. This was responsible for a significant loss in alfalfa seed germination when values from all three locations were pooled. There was evidence that the California alfalfa seed had been thresher-damaged which could account for this loss in germination. The 1981 germination values for timothy were significantly higher than in 1961 but this probably was due to testing procedures used in 1961. Excluding the timothy seed lots, the mean germination for the remaining 231 seed lots declined less than 2% after 20 years of subfreezing storage. High quality bromegrass seed is not limited to 12 years of subfreezing storage as earlier concluded.

Key Words: Seed germplasm preservation • Seed longevity

² Research agronomist, USDA, ARS, Prosser, WA 99350.

Received for publication April 26, 1982.