Survival of Sesame Seeds at the Temperature (−196°C) of Liquid Nitrogen1

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Abstract
Preserving valuable seed germplasm in liquid nitrogen (LN2) has the potential of extending the storage life of the sample almost indefinitely. However, during the cooling and rewarming process, temperature related stresses occur that can be lethal to many biological materials, including seeds. The capacity of seeds to withstand LN2 cooling is critical to long‐term cryopreservation of these germplasm samples. Seeds from six sesame (Sesamum indicum L.) selections were used to develop procedures to overcome cryogenic damage during the LN2 cooling/rewarming process. Seed moisture content and cooling rate were identified as controlling factors in the survival of sesame seeds exposed to LN2. As seed moisture content increased from 60 to 120 g kg−1 and cooling rate increased from 10 to 200°C min−1, mortality increased. Regardless of cooling rate, all seeds of all selections were killed at moisture content levels above 120 g kg−1. At seed moisture contents below 60 g kg−1 and cooling rates of 1, 10, and 30°C min−1, all seeds of all sesame selections tested survived. At a 200°C min−2 cooling rate and moisture contents below 60 g kg−1, four of the six selections were damaged. Results from this study suggest that sesame seeds can tolerate LN2 exposure if the seed moisture content is below 60 g kg−1 and the cooling rate is between 1 and 30°C min−1.