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Effect of alternate freezing and thawing on the impermeability of alfalfa and dodder seeds

Midgley, A.R.
Agronomy journal 1926 v.18 no.12 pp. 1087-1098
Medicago sativa, Cuscuta, seed germination, seeds, absorption, freezing, thawing, permeability
Alfalfa seed contains a high percentage of impermeable seeds. After the first freezing, subsequent freezing and thawing seem to have very little influence in reducing the number of impermeable alfalfa seeds. The first freezing is by far the most effective. It reduced the number of impermeable seeds about 23%, on the average. The intensity of freezing has no influence in reducing the impermeability. A temperature of 0 degrees C. is fully as effective as -20 degrees C. When kept in a moist condition for several months as many seeds will germinate without freezing as a similar sample frozen each week during the same length of time. This would indicate that freezing only expedites the process. The length of time the seeds are kept moist seems to be more important. Alfalfa seed becomes permeable with age even when left in a dry condition. However, the rate is very slow when the seeds are stored at room temperature with little or no variation in temperature. Freezing the seeds in a dry condition seems to be as effective as when the seeds are wet and frozen. This is especially true for the first freezing. It would seem from this that the warehouse that allows for seasonal changes in temperature would be beneficial in causing alfalfa seed to become permeable. The duration of freezing seems to have no influence on germination. As many seeds became permeable and germinated after one hour of freezing as when a similar sample was frozen for 60 days. The duration of thawing with subsequent freezing has very little influence in producing permeable seed, but it has a marked effect on the number of seeds that are killed. The longer the thaw, the greater the number of seeds that are killed with subsequent freezing. This strongly indicates that seeds which become permeable with one freezing are killed by the next. The number of impermeable seeds in alfalfa varies according to the color of the seeds. The nearer the seeds approached the true color of bright yellow the more impermeable seeds were found. Green seed had a higher percentage of impermeable seeds than brown. Alternate freezing and thawing has very little or no influence in reducing the number of impermeable dodder seeds. An average of only 8% germinated after 20 freezings, and of this number one-half germinated before freezing. The alfalfa seed used in these experiments proved to be almost 100% viable when a test was made with sulfuric acid or scarification. The dodder seed used was found to be at least 70% viable with the sulfuric acid treatment.