E. R. Joachim Keller

Potato Shoot Tip Cryopreservation. A Review

Potato is one of the most important crops worldwide. Genetic resources of potato (Solanum tuberosum L. ssp. tuberosum) and related cultivated species are conserved through storage of tubers, in vitro plants and in cryopreservation. Cryopreservation, storage in or above liquid nitrogen, is the best option to maintain vegetatively propagated plants in the long term. The present review gives comprehensive information about various cryopreservation techniques for potato published from 1977 until the present. It discusses factors that affect the process and success of cryopreservation, such as donor culture conditions, preculture, cooling, warming and post-culture treatments. Studies are presented that analyse the histological and ultrastructural changes after different cryopreservation steps and the morphological pathways during regeneration of plants after rewarming. The maintenance of genetic stability in potato after cryopreservation has also been demonstrated by various phenotypic and molecular methods. The first thermal analyses on potato shoot tips are presented using differential scanning calorimetry to analyse the state of water during cooling and warming. Biochemical analyses of different compounds, such as soluble sugars and proteins, have been performed to understand and improve existing cryogenic methods. Potato is an example where successful virus elimination has been obtained via cryopreservation of shoot tips (cryotherapy). There are already cryopreserved collections of potato shoot tips in Germany, Peru, Czech Republic, South Korea and USA, but additional experiments on fundamental aspects of potato cryopreservation will help to improve understanding of the different cryopreservation methods, start new collections in other countries and also build up existing cryocollections of potato.

Genetic identity of three mint accessions stored by different conservation procedures: field collection, in vitro and cryopreservation

At the genebank of IPK (Leibniz Institute of Plant Genetics and Crop Plant Research) in Gatersleben, Germany, three long-term conservation methods (field genebank, in vitro slow-growth and cryopreservation) are used for mint germplasm. The plant material of the field genebank was the source to establish the slow-growth in vitro culture collection, from which the cryopreserved collection was set up, using a droplet-vitrification protocol. The genetic identity of 161 samples of three mint accessions (MEN 198, MEN 166 and MEN 186), stored for several years using those three methods, was studied using RAPD markers. Accession ‘MEN 198’ was the only one with a unique RAPD fragment pattern for all its samples, independently of the conservation procedure employed. The field collections of accessions ‘MEN 166’ and ‘MEN 186’ were made up of different genotypes. None of the genotypes detected in the plots of these accessions was represented in the in vitro and cryopreserved samples analyzed, which showed a unique genotype for each accession. From this work we conclude that, for an appropriate management of a germplasm collection of vegetatively propagated species, the determination of the genetic composition of the donor material and a periodical assessment of the preserved material should be carried out.

The Garlic and Shallot Core Collection image database of IPK presenting two vegetatively maintained crops in the Federal ex situ genebank for agricultural and horticultural crops at Gatersleben, Germany

Garlic and shallot are important vegetable and spice plants, garlic is also a medicinal crop widely used throughout the world. Both belong to the genus Allium, which has been a main target of the taxonomical research at the IPK for many years. Therefore, the IPK’s living collection of Allium is one of the world’s largest special collections of this genus with garlic and shallot being essential parts of this collection. Furthermore, they are subject to special activities to preserve the material in vitro and in cryopreservation. Both methods help protecting valuable germplasm from abiotic and biotic threats and reduce the maintenance costs in the long term. At present, the garlic collection maintained at the IPK incorporates germplasm of 509 accessions in total including all safety duplicates not offered for exchange. Of shallot, 114 accessions are present as well. Passport data as well as phenotypic data of 159 accessions of garlic, one of great headed garlic and 16 of shallot are included in the Garlic and Shallot Core Collection Database (GSCC). An additional part of the database is a comprehensive collection of images illustrating morphological characteristics of the accessions. Exploration of the information is supported by a web-based application. The GSCC is available at http://www.ipk-gatersleben.de/databases/gscc.

Allium Genetic Resources

An overview of the developments in Allium genetic resources during the past 25 years is presented in this chapter. A first important development has been the introduction and further development of web-based genebanking information systems (e.g. GENESYS, PLANTSEARCH), which facilitated the exchange of data to a large extent between Allium collection holders worldwide. These information systems made it possible to obtain an overview of the Allium genetic resources managed worldwide and identify the gaps in collections which still need to be filled, especially in the face of the ongoing genetic erosion. A second important area of progress has been the development of new methods for the maintenance of Allium germplasm, especially cryopreservation. This method has made it possible to maintain Allium accessions in a cheap and effective way. The method is especially important for the conservation of vegetatively maintained germplasm. Other developments in Allium genebanking are the improvement of the health status of the germplasm kept in the collections and the continuing characterization and evaluation of germplasm, which stimulates the utilization of the Allium genetic resources held in genebanks. Significant changes could also be observed with respect to acquisition and exchange of plant genetic resources due to many and complex new regulations on the legal and organizational levels due to the adoption of the CBD and IT-PGRFA by many countries. It makes the handling of the plant accessions safer and more consistent but also more circumstantial. Finally, we need to underline that in an increasingly changing world with all the threats of genetic erosion and extinction due to disappearance of traditional cultivation methods, devastation of our environment and climatic change, the conservation of genetic resources is of prime importance for agriculture. Especially for breeders, a highly diverse genepool of a crop plant is an invaluable treasure. The importance to keep this treasure will no doubt become even more important in the future.

The changes in the reproductive barrier between hexaploid wheat (Triticum aestivum L.) and rye (Secale cereale L.): different states lead to different fates

AbstractMain conclusionThe changes in the reproductive barrier between hexaploid wheat (Triticum aestivumL.) and rye (Secale cerealeL.) can be induced using in situ embryo rescue of abnormal embryos, yielding stable fertile amphidiploid plants. In intergeneric crosses between hexaploid wheat (Triticum aestivum L.) and rye (Secale cereale L.), postzygotic barriers may occur at different stages of hybrid development. One such mechanism is embryo lethality, which is genetically determined by the interaction and expression of two incompatible genes in wheat (Eml-A1) and rye (Eml-R1). Using in vitro culture methods as stressors, we overcame this hybrid lethality. Normal and abnormal embryos were observed to build embryogenic calli and produce regenerated plantlets in a similar manner. The high regenerative capacity of the abnormal embryos led us to conclude that the reproductive barrier in these intergeneric hybrids may have an epigenetic origin that can be easily overcome by culturing immature embryos via callus induction. After colchicine treatment during callus culture, amphidiploid plants were obtained. However, most of these plants did not produce seeds, due mainly to sterility of the pollen but also of the embryo sacs. These findings demonstrate that hybrid sterility affects both male and female gametophytes in plants obtained from abnormal embryos. The key roles of double fertilization and stress factors in the implementation of the apical meristem formation program in embryos from incompatible intergeneric crosses between hexaploid wheat and rye during in vitro culture are discussed. We also propose a hypothetical model for a wheat–rye lethality system involving differential expression of incompatible wheat Eml-A1 and rye Eml-R1b alleles in an identical genetic background.