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    Langzeitlagerung von Saatgutproben in „ultra dry seed storage“ zur Lagerung pflanzengenetischer Ressourcen in Genbanken
    (2011) Yang, Qi; Kruse, Michael
    The conservation of plant genetic resources through seed storage in gene banks is primarily restricted to relatively short lived plants with orthodox seeds, to which most agricultural and horticultural species belong. Their storage properties are influenced by two key factors, seed moisture content and storage temperature. Ultra-dry seed storage follows the theory that drying seeds to sufficiently low moisture contents could achieve successful long-term seed storage even at room temperature. The artificial freezing storage of seeds, which is usually used in modern gene banks, would not be required. This is very attractive for the gene banks in developing countries where energy supply is limited. The following questions are still remained to be answered for the realization of ultra-dry seed storage. - Will the seeds be damaged by drying close to 0 % moisture content? - Is there for ultra-dry seed storage optimal moisture content (OMC) or optimal relative humidity (ORH) as well as a respective upper and lower limit above 0%? - If such upper and lower limits exist, are they identical among species? - How good is the storability of the seeds under ultra-dry conditions? Does the improved seed viability equation of Ellis and Roberts (1980) also apply to the ultra-dry region? Seed samples of the four breed lines HR2203, HR2632,HR2660 and HR2693 of rape seeds (Brassica napus L.), the three cultivars Naturastor, Tomi and Triso of wheat (Triticum aestivum L.) and the two cultivars Giugenese and Sturo of onion (Allium cepa L.) were used. The moisture contents (MC) of onions, rape seed and wheat were adjusted separately to 39 different levels from near 0 % to 7 % in sealed desiccators with silica gel (r.H. close to 0 %) or in the fine-drying chamber (r.H. about 10 %) of the gene bank at IPK-Gatersleben. The dried seed samples were sealed individually in aluminum foil to keep the MC. The equilibrium relative humidity was determined after 14 days by using a metal thread sensor. Sorption isotherms were created according to these data. The wheat and the rape seed samples were then stored at 50 °C for about one year and eight months, respectively. The onion seeds were stored at room temperature for about one year and subsequently stored at 50 °C for up to three months. The germination and seed vigor tests were performed during storage. The experimental results reveal that the Henderson model fits the experimental moisture sorption data better than the modified GAB and Chung-Pfost equation and is therefore suggested for modeling the correlation between the equilibrium moisture content and the relative humidity in ultra dry region. The germination and seed vigor tests indicate that the seed storability increases along with decreasing seed moisture contents till an optimum is reached. There is clearly an optimum seed moisture content (OMC) for the ultra-dry seed storage, below which the storability decreases significantly. The OMC for storage at 50 °C are 4 % and 3.1 % for rape seeds breed lines HR2203 and HR2632, 2.3 % and 2.0 % for the wheat cultivars Naturastor and Triso, as well as 1.9 % and 1.5 % for the onions cultivars Giugenese and Sturo. The corresponding optimum relative humidity (ORH) in balance are 42 %, 22 %, 11 %, 6 %, 1 % and 3 %, respectively. The OMC for the storage of onion cultivars Giugenese and Sturo at about 20 °C are 2.7 % and 1.9 %, and the corresponding ORH are 2 % and 5 %, respectively. Thus, the OMC and ORH are not only species specific, but also cultivar- and possibly also seed lot-specific and temperature dependent. The improved seed viability equation can be used to describe the seed storage behavior above the OMC adequately. The seed storage behavior below the OMC could be described with polynomials. Based on the obtained data it is not possible to give a general recommendation for upper and lower limits of the seed moisture content or relative humidity for a successful ultra dry storage. The storage property of rape seed stored at OMC is better than those of wheat and onion seeds; although under normal conditions the storability of wheat is better than that of the other two species. Calculated from obtained data rape seed with 99 % initial germination lost only 0.14 % of germination during one-year storage at 50 °C. Contrary to the hitherto conventional evaluation of the storage behavior of seeds, the experimental results showed that the temperature and seed moisture content do not affect storage property of seed independently and their effects cannot be offset against each other in the ultra dry region. Extrapolated to the ultra-dry seed storage at ambient temperature in a gene bank it can be assumed that the seed can be stored safely for at least 3 years. Longer storage is possible, but it is required to keep the seed of different species, cultivars and even seed lots at their specific OMC. The separate determination of OMC for all accessions in a gene bank is practically difficult to carry out. Thus, it is recommended for long-term storage in gene banks to store seed samples at appropriate low seed moisture contents from 1.5 % to 4.0 % and under cool conditions as a precaution.