Changes in Trifolium arvense Seed Quality Following Alternating Temperature Treatment using Liquid Nitrogen

Abstract

The effects of alternating temperatures, using liquid nitrogen(−196 °C) as the low temperature phase, on Trifolium arvense L. seed quality was investigated. Treatment reduced hardseededness with the seeds exhibiting a linear increase in the probit of germination with the logarithm of the number of alternating temperature cycles. Germination levels equal to ‘chipped’ controls were achieved after four cycles or more, depending on the initial depth of hardseededness, and the response was unaffected by either the rate of cooling or the rate of warming. Imbibition time was reduced with increasing alternating temperature cycles. Resealing experiments identified the main area of water uptake as the lens, and SEM showed that deepening of already present cracks may be important in removing hardseededness. Pre-treatment of seeds with alternating temperatures predisposes the seeds to subsequent damage by sulphuric acid treatment, but not by impaction. Stress effects were not restricted to the seed coat surface as between 10 and 20 % of seeds treated for 3–15 cycles developed into abnormal seedlings with detached cotyledons. Seed vigour is also reduced as treatment leads to contraction of the temperature response curve for germination. The results have implications for the cryopreservation of papilionoid legume seeds as a means of genetic conservation.