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Published in Issue No. 122, page 41 to 43 - (6548) characters

A comparative study on the seed germination of selected species at the Gatersleben genebank to test the effect of freezing and rewarming on germinability

C.E. Specht  A. Meister  A. Börner  Introduction

At present the Gatersleben genebank collection consists of 100 000 accessions, approximately 87% of which are stored at either 0°C or -15°C. The effect of long-term storage under the conditions at the Gatersleben genebank, on the germinability of certain species, has already been published (Specht et al. 1997, 1998).


Because of the lack of space, to date the whole collection has not been divided up into a base collection and an active one, as suggested in genebank standards (FAO/IPGRI 1994). Therefore, if there is a request for seeds of a certain accession, it is common practice to take seeds, particularly in the case of cereals and legumes, from lots that have been stored for up to five years after harvesting outside the cold-storage facilities at room temperature. In general, for seeds harvested more than five years ago samples are taken from corresponding lots stored since harvesting in cold-storage facilities at 0°C or -15°C. In such cases, the storage containers are taken out of the cold chambers and transferred to a climatic chamber for acclimatization. After 24 hours within this chamber, which has a controlled temperature of 10°C and a humidity of 60%, the containers are opened, the seeds taken out and the container returned to the cold-storage facilities.


The research described in this paper aimed to investigate whether the common practice of freezing and rewarming has a negative effect on the germinability of stored seeds, particularly since, in total, about 13 000 samples are requested annually (IPK Annual report 1999). For this study four species were chosen which are known to differ under long-term storage conditions (Specht et al. 1997): for cereals (Triticum aestivum and Secale cereale), for legumes (Pisum sativum) and for vegetables (Allium cepa). Triticum aestivum and P. sativum were found to maintain germinability for nearly two decades under the Gatersleben storage conditions. By contrast, S. cereale was found to lose germinability rapidly after one decade, whereas the percentage of germination for A. cepa was generally low from the beginning.



Material and methods


One accession each of T. aestivum, S. cereale, P. sativum and A. cepa was selected at random from the collection (Table 1). The initial germinability was determined and afterwards the seed samples were divided up into two lots, one kept in cold storage facilities at -15°C and the other rewarmed (10°C) and then frozen (-15°C), day after day for up to 200 times. During the whole investigation, the moisture content of the seeds was kept between 8-9%, similar to the moisture content during long-term conservation in the genebank. After having frozen/rewarmed seed lots 20, 40, 60, 80, 100, 120, 140, 160, 180 and 200 times the seeds were tested for germinability. As a control, germination tests were performed on the lots kept at -15°C throughout the experiment. All germination tests were conducted according to the international rules for seed testing (Anonymous 1996) in paper rolls for T. aestivum, S. cereale, P. sativum and on filter paper on a Jacobsen apparatus for A. cepa. For statistical analysis the exact 95% confidence intervals were calculated after Fagan (1996).



Results and discussion


The results presented in Figures 1 - 4 show only slight differences in germinability of seeds for the four species tested, even after 200 freezing-rewarming cycles. For T. aestivum the maximum loss in germinability detected within the test series was 5% (Fig. 1), while A. cepa had the highest loss at 24% (Fig. 4). However, the final result obtained after the seeds had been submitted to 200 freezing-rewarming cycles shows an insignificant difference in germinability of less than 5% for all four species. The absence of significant differences between the species tested was surprising, because from the results of long-term storage tests (Specht et al. 1997) differences in the response of these species had been expected.


For T. aestivum and P. sativum it has been demonstrated that a high germinability is maintained for a period of at least 15 years, while for S. cereale the percentage of germination declines after 12 years and it is generally low with A. cepa. There seems to be no difference between germination after long-term storage or after a high number of freezing-rewarming cycles. One explanation for this may be that the physiological processes responsible for the reduction in germinability do not commence until after 24 hours at a warmer temperature.


The results obtained in this study may influence practical genebank work as splitting collections into base and active collections may not be required. In the Gatersleben genebank, for example, approximately 10 000 seeds are stored in one single container per cereal accession. If 50 seeds per sample are distributed to users, the glass container will be empty after 200 samples have been taken out. At present, it is not known whether there is any interaction between long-term storage and a high number of frequent temperature changes that would influence germinability. To verify this, a comparable experiment needs to be designed, using seed samples stored for a longer time at the seed store than those investigated here.



Acknowledgements

The authors wish to thank Martina Egler and Sibylle Pistrick for carrying out the germination tests.



References


Anonymous. 1996. International rules for seed testing. Seed Sci. Technol. 24, Suppl. Rules.

FAO/IPGRI. 1994. Genebank Standards. Food and Agriculture Organization of the United Nations, Rome/International Plant Genetic Resources Institute, Rome, Italy.

Fagan, T. 1996. Quick basic program for exact and mid-P confidence intervals for a binomial proportion. Comput. Biol. Med. 26:263-267.

IPK. 1999. Annual Report - Report of the genebank department. IPK, Germany.

Specht, C.-E., E.R.J. Keller, U. Freytag, K. Hammer and A. Börner. 1997. Survey of seed germinability after long-term storage in the Gatersleben genebank. Plant Genet. Resour. Newsl. 111:64-68.

Specht, C.-E, U. Freytag, K. Hammer and A. Börner. 1998. Survey of seed germinability after long-term storage in the Gatersleben genebank (part 2). Plant Genet. Resour. Newsl. 115:39-43.

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