CGN cucumber collection
The collection
In short- Support for breeding activities
- Maintaining genetic diversity
- Part of the fruit vegetables collection
Cucumber is part of the Cucurbitaceae family and is closely related to melon, watermelon and pumpkin. Cucumber is one of the top ranking vegetables in terms of global production.
Composition
The cucumber collection of CGN is mainly composed of cultivated cucumber (Cucumis sativus) and currently holds over a thousand accessions. A few accessions of the subspecies C. sativus var. hardwickii and C. sativus var. sikkimensis are present. CGN’s cucumber collection is one of the largest collections in Europe and comprises cultivars, landraces, and research material, as well as C. sativus var. hardwickii, which is considered to be the wild form of cucumber. 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 consists of cultivars originating from Europe. Unique landraces have been collected from countries such as Egypt, Pakistan, Kyrgyzstan, and Uzbekistan.
Maintenance
Cucumber accessions are regenerated in case of insufficient seed viability or nearly depleted seed stocks. Breeding companies assist in the regeneration of cucumber. Regeneration takes place in insect-free glasshouses on a substrate system where the stems are grown along ropes. Cucumber is a cross-fertilising species, so ten plants are used for regeneration. Fourteen plants are used in the case of heterogeneous samples. During the growing season, plants are monitored by the Dutch Plant Health Service for seed-borne diseases in order to prevent seed contamination.
Characterisation
The characterisation of fruit vegetables takes place during regeneration. Until 2006, about 30 descriptors were used for each crop. Since 2006, the fruit vegetables are characterised using minimum descriptors developed by the ECPGR Working Groups. The minimum descriptor list for cucumber consists of eleven descriptors and can be found at the ECPGR Cucurbits webpage. All characterisation data are made available online and in downloadable files on CGN’s website. The collections are well photo-documented, with many pictures of (un)ripe fruits, plants, and flowers available.
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 of this study have been shared with CGN and were used to improve the data and composition of the collection.
Evaluation
In the period 2001-2006, over 100 accessions were screened for resistance to powdery mildew (Sphaerotheca fuliginea) and downy mildew (Pseudoperonospora cubensis). The entire cucumber collection was screened for Cucumber Green Mottle Mosaic Virus (CGMMV) in 2008.
Regeneration of cucumber
Seed dormancy
Some cucumber accessions germinate irregularly. It is unknown whether this is caused by seed dormancy. Germination can sometimes be improved by cutting off the top of the seed.
Vernalization
No vernalization takes place during the regeneration of cucumber.
Sowing
Before sowing, seeds are given a heat treatment to avoid infection with seed-transmittable viruses like CGMMV.
Seeds are sown in seed trays with a soil mixture at 25°C, generally in February, but it is possible to sow between January and July. After 7 to 30 days, the seedlings are transplanted to Rockwool blocks and placed in a glasshouse nursery on tablets with a temperature of 23/20°C day/night and additional light.
Planting
About six weeks after sowing, the plants in the Rockwool blocks are placed on Rockwool bags at a distance of 50 cm in the row and 100 cm between the rows. The distance between rows can differ due to the substrate system used. The temperature in the greenhouse is keptat 23/20°C day/night. The plants are grown along wires. Per plant two stems are maintained since most cucumbers are indeterminate. Plants are pruned weekly.
The plants are grown in glasshouses free of pollinating insects so it is not necessary to take precautions for uncontrolled pollination. In case that a plant gives predominantly male flowers, it is possible to obtain female flowers by pruning. If pruning does not help, the plant can be sprayed with ethylene. Plants with only female flowers can produce male flowers after a treatment of the sprouts with 250 ppm silver nitrate. For seed production, a so-called chain pollination is carried out by hand. Per accession, plant no. 1 is crossed with plant no. 2, plant no. 2 with plant no. 3, and so on.
Generally 10 plants are used per accession for regeneration. In case of heterogeneous accessions or accessions with low seed production, more plants are used. The number of plants per accession is limited due to the high input in labour and capital.
Harvesting
Fruits are harvested about four months after sowing at the physiological ripe fruit stage. This is much later than the marketing stage. Per plant the aim is to produce two to four ripe fruits which can be harvested. Fruits are harvested in several rounds when they are ripe and stored for at least a week before seed extraction.
Pest and Disease Control
Biological control:
- Spider mites with Phytoseiulus persimilis
- Thrips with Phytoseiulus persimilis andOrius laevigatus
- White fly withAphidius colemani
- Aphids withEncarcia formosa
Non-preventive pesticide treatments:
- Spider mites, in case biological control is not effective
- Grey mould (Botrytis spp.)
- Gummy stem blight (Didymella spp.)
- Powdery mildew (Sphaerotheca fuliginea)
During regeneration, the plants are checked visually for diseases by the Dutch Plant Health Service. In case of doubt the plants are tested to determine the disease. Infected plants are removed.
Gene bank for plant resources
View the database or submit a request for genetic material.
Do you have a question?
Do you have a question about the cucumber collection? Ask our curator:
LJMJ (Lynn) Vorstenbosch
DLO HBO Onderzoeker
