CGN cucumber collection
The history of the cucumber collection is analog to the CGN collections of tomato, pepper, eggplant and melon and described in the general page of the fruit vegetables.
The cucumber collection of CGN is only composed of the cultivated Cucumis sativus and holds currently 925 accessions. A few accessions of the subspecies C. sativus var. hardwickii and C. sativus var. sikkimensis are present. It is one of the largest collections in Europe and comprises of 371 cultivars, 137 landraces, 16 accessions of research material, 4 accessions of C. sativus var. hardwickii which is considered to be the wild form and 397 accessions of unknown population type which will be improved when more information is available. A diversity study with molecular markers revealed that the landraces are genetically clustering apart from the rest of the collection (Ly et al. 2012). A quarter of the collection are cultivars originating from Europe of which 154 Dutch accessions. Unique landraces have been collected in Egypt, Pakistan, Kyrgyzstan and Uzbekistan.
To be incorporated in the collection, accessions need to have a minimum seed viability of 80% for cultivated material and 60% for accessions of wild species. Regeneration is carried out when seed viability is to low or when the remaining seed quantity has dropped below 12.5 g. Regeneration/multiplication takes place in insect-free glasshouses on a substrate system where the stems are grown along ropes.
For cucumber, which is a cross-fertilizing species, ten plants are used. When samples are heterogeneous, fourteen plants are used. Breeding companies, organized in Plantum NL, assist in the regeneration of cucumber. Accessions which are difficult to regenerate are placed in isolation cages with bumble bees for pollination. During the growing season plants are monitored by the Dutch Plant Health Service for seed borne diseases in order to prevent seed contamination.
Characterization of fruit vegetables takes place during regeneration. Almost all accessions have been morphologically described. Until 2006 about 30 descriptors were used for each crop. Since 2006 the fruit vegetables are characterized by minimum descriptors developed by the ECPGR Working Groups. The minimum descriptor lists consist of about ten descriptors per crop and can be found at the ECPGR Cucurbits webpage. All characterization data are made available on-line and in downloadable files. The collections are well photo-documented, many pictures of (un)ripe fruits, plants and flowers are available. When necessary new pictures will be taken during regeneration and added to the CGN website.
In 2009 the Institute of Vegetables and Flowers of the Chinese Academy of Agricultural Sciences in Beijing, China used 80% of the CGN cucumber collection in a diversity study with SSR markers in order to develop a core collection (Ly et al. 2012) The results have been shared with CGN and were used to improve the data and composition of the collection.
In the period 2001-2006 a total of 134 accessions were screened for resistance to powdery mildew (Sphaerotheca fuliginea), and downy mildew (Pseudoperonospora cubensis). The entire cucumber collection has been screened for Cucumber Green Mottle Mosaic Virus (CGMMV) in 2008.