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- Author or Editor: Phillip C. Stanwood x
- Journal of the American Society for Horticultural Science x
Seeds of 5 cultivars of lettuce (Lactuca sativa L.) were adjusted to moisture contents between 5 and 22% and subjected to temperatures of 5, -18, -70, and -196°C (liquid nitrogen) for 7 days. Seeds with moisture contents up to 18% were not damaged by either -18 or -196°C; however, the -70°C treatment resulted in loss of germination even with seeds containing as little as 16% moisture. Seeds held at 5°C showed no loss in viability. The loss in germination at -70°C appeared to be related to cooling rate. High moisture (18 to 20%) seeds were cooled to -196°C at different rates from 1 to 200°C/min. Germination was reduced in seeds cooled at rates slower than 25°C/min. At 200°C/min cooling rate and 18 to 20% seed moisture both germination and root growth occurred although at reduced levels compared with control seeds held at 5°C. Prolonged storage (33 days) in liquid nitrogen of rapidly frozen high moisture lettuce seeds did not result in further loss of germination after the initial freezing to -196°C.
Dehydration effects on freezing characteristics and survival in liquid nitrogen were studied in 11 species of tropical seeds and in silver maple (Acer saccharinum L.) seeds. Differential thermal analysis was used to determine the threshold moisture level below which seed tissue water was in an unfreezable state. Desiccation-sensitive seeds, areca palm [Chrysalidocarpus lutescens (Bory) Wendl.] and silver maple, did not survive dehydration below the threshold moisture level and did not survive exposure to liquid nitrogen. Nine of 10 desiccation-tolerant seeds [strawberry guava, Psidium cattleianum Sabine; passion fruit, Passiflora edulis f. flavicarpa Deg.; Ceara rubber, Manihot glaziovii Mull. Arg.; dwarf schefflera, Schefflera arboricola (Hayata) Merrill; common guava, Psidium guajava L.; papaya, Carica papaya L., apple of sodom, Solarium sodomeum L.; prickly poppy, Argemone glauca Pope; and seamberry, Sabalparviflora Becc.] survived dehydration to as low as 2% to 12% moisture content (below the threshold moisture levels determined) and in the dehydrated state survived exposure to liquid nitrogen. Coffee (Coffea arabica L. var. Bourbon) seeds tolerated dehydration to as low as 8% moisture content but did not survive exposure to liquid nitrogen. These results demonstrate the feasibility of cryopreserving seed germplasm of several tropical species.