CGN lamb’s lettuce collection
The collection
In short- Established in 2010
- Cultivated and wild accessions
- one of the biggest lamb’s lettuce collections in the world
Lamb’s lettuce (or corn salad) is a relatively small crop assigned to the group of minor leafy vegetables. The lamb’s lettuce collection was established in 2010 and contains a diverse selection of cultivated and wild accessions of various Valerianella species.
History
CGN adopted a new policy in 2010 to specialise in vegetable crops which resulted in the development of several new crop collections. These new collections also included lamb’s lettuce, due to its relatively poor representation of genetic resources in existing collections and the importance of the crop to the Netherlands. Nowadays, the collection is one of the biggest lamb’s lettuce collections in the world.
Composition
Collection development started in 2011 with the acquisition of important Dutch varieties of cultivated lamb’s lettuce (Valerianella locusta). Some degree of overlap exists between CGN and the German collection since a selection of important Dutch varieties was obtained from the German genebank in Gatersleben. Subsequently, the collection was extended with cultivars and landraces originating from other European countries, in particular Germany and France, as far as the material was not yet properly conserved and distributed by other national gene banks.
In 2013, CGN started with sampling natural populations of V. locusta in the Netherlands, followed by collecting specimens of related species occurring in the Netherlands, including V. carinata, V. dentata and V. rimosa.
In 2024, CGN organised a collecting expedition together with INHORT, the Research Institute of Horticulture in Skierniewice, Poland. This expedition resulted in the addition of over 50 wild accessions from West and South Poland to the lamb’s lettuce collection.
Maintenance
Lamb’s lettuce accessions are regenerated in case of insufficient germination or depleted seed stocks. Lamb’s lettuce is sown in November and plants are overwintered under frost proof greenhouse conditions. Due to the selfing nature of lamb’s lettuce, regeneration can be carried out without specific protective measures to avoid pollination between accessions. A few meters distance is maintained between accessions to minimise the risk of contamination. Seed harvesting takes place in May or June.
Characterisation
Lamb’s lettuce accessions are described using the minimum descriptor list for Valerianella developed by the ECPGR Working Group on Leafy Vegetables. The minimum descriptor list for Valerianella and other leafy vegetables can be found at the ECPGR Leafy Vegetables webpage. The characterisation is further expanded upon using descriptors originating from the testing guidelines of UPOV.
Phenotypic data for cultivars that were described by the Netherlands Inspection Service for Horticulture (Naktuinbouw) are made available as downloadable files on CGN’s website. In 2019, the entire collection was grown in a field trial and described for various morphological traits. These data and pictures of the accessions are also available from CGN’s website.
Regeneration of lamb’s lettuce
Seed dormancy
Seeds of cultivated lamb’s lettuce (Valerianella locusta) sometimes display dormancy. Seed dormancy can be overcome through a cold treatment by placing the seeds at 5°C for 3 days after sowing.
Vernalization
Flowering is induced by overwintering the plants in a frost-proof greenhouse.
Sowing
Seeds of cultivated lamb’s lettuce are sown mid-November in seed trays. After the dormancy breaking treatment, the trays are placed at 20°C in the greenhouse for a period of 1 to 2 weeks. After full development of the cotyledons, seedlings are transplanted to small pots.
Planting
Plants are raised in the greenhouse at 16-18 °C for a period of 1 month. During this period, plants of sufficient size are transplanted to larger pots. Starting in January, overwintering takes place in a frost-proof greenhouse. Plants are supported by wooden stakes to prevent lodging. Homogeneous accessions are regenerated with 10 plants, while 20 plants are used for heterogeneous samples such as landraces and wild species.
Pest and disease control
During the regeneration, plants are checked for the presence of pests and diseases, in particular aphids and fungi, and treated when necessary. After planting in the greenhouse, the plants are visually inspected several times by the Dutch Plant Protection Service for the presence of viruses. Only healthy plants are maintained for seed production.
Harvesting
Soon after the seed colour changes from green to yellow/brown and the beginning of seed shattering, above-ground plant parts are cut off and placed on a piece of cloth or plastic in the greenhouse until majority of the seeds have ripened. After sufficient ripening, seeds are carefully removed from the inflorescences and plant parts are discarded as much as possible. Subsequently, the seeds are dispersed on the cloth/plastic for further ripening and drying. Seeds are then collected in paper bags and transferred to the drying and cleaning facility. Flowering and seed production usually take place during May and/or June.
Gene bank for plant resources
View the database or submit a request for genetic material.
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LJMJ (Lynn) Vorstenbosch
DLO HBO Onderzoeker
