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Title: While they were asleep: Do seeds after-ripen in cold storage? Experiences with Calendula

Author
item Widrlechner, Mark

Submitted to: International Plant Propagators Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/8/2007
Publication Date: 11/13/2007
Citation: Widrlechner, M.P. 2007. While they were asleep: Do seeds after-ripen in cold storage? Experiences with Calendula. International Plant Propagators Proceedings. 56:377-382.

Interpretive Summary: Methods to break seed dormancy are of great value to plant propagators, who typically want quick methods that consistently result in high germination rates without large labor inputs. But if time is not crucial, some seeds may eliminate their internal dormancy mechanisms during storage. This progressive loss of dormancy after seed maturity is known as after-ripening. Although after-ripening is well understood in seeds stored at relatively high temperatures, little is known about this process at lower temperatures (e.g. 40 degrees F) generally used for seed storage. This paper presents an example using historical germination data from the USDA-ARS North Central Regional Plant Introduction Station (NCRPIS), Ames, Iowa, to help determine whether stored Calendula seeds are just at rest or are also slowly losing dormancy. Germination data from all seed lots of Calendula accessions regenerated and stored at the NCRPIS were downloaded from the Germplasm Resources Information Network. Data were retained for analysis only when a seed lot was tested on three or more occasions over at least 9 years of storage. On that basis, I analyzed 81 germination tests from 24 stored seed lots, representing three Calendula species. These lots could be divided into two general groups. Those with high initial germination rates (greater than 50% normal seedlings) exhibited only minor increases in germination over time in cold storage. But lots with low initial germination rates (less than 50% normal seedlings) exhibited marked increases in germination percentage during storage for the first 6.5 years, followed by a decline, expected as a result of seed aging. The following practical recommendations were made to propagators. First, seeds that have spent many years in cold storage may not require typical dormancy-breaking techniques. Second, if new seeds with unknown dormancy requirements need to be germinated, it might be wise to retain a subset in cold, dry storage for at least a few years. And finally, seeds in cold storage may after-ripen more effectively if they are first held at room temperature before transfer to cold storage.

Technical Abstract: The progressive loss of seed dormancy after maturity is known as after-ripening. Although after-ripening is generally well understood in seeds stored at relatively high temperatures, little is known about this phenomenon at lower temperatures (e.g. 4 degrees C) generally used for medium-term seed storage. This paper presents a retrospective analysis of historical germination data from the USDA-ARS North Central Regional Plant Introduction Station (NCRPIS), Ames, Iowa, to help determine whether stored Calendula seeds are truly quiescent or are also slowly losing dormancy. Germination data from all seed lots of Calendula accessions regenerated and stored at the NCRPIS were downloaded from the Germplasm Resources Information Network. Data were retained for analysis only when a seed lot was tested on three or more occasions over at least 9 years of storage. On that basis, 81 tests from 24 stored seed lots, representing three Calendula species, were analyzed. These lots could be divided into two general groups. Those with high initial germination rates (greater than 50% normal seedlings) exhibited only minor increases in germination over time in cold storage. But lots with low initial germination rates (less than 50% normal seedlings) exhibited marked increases in germination percentage during storage for the first 6.5 years, followed by a decline, expected as a result of seed aging. The study produced the following practical recommendations. First, seeds that have been held for many years in cold storage may not require typical dormancy-breaking techniques. Second, if new seeds with unknown dormancy requirements need to be germinated, it might be wise to retain a subset in cold, dry storage for at least a few years. And finally, seeds in cold storage may after-ripen more effectively if they are first held at room temperature before transfer to cold storage.