CGN lettuce collection

The lettuce collection originates from the former Institute for Horticultural Plant Breeding (IVT), whose working collection was adopted by CGN in 1985. Afterwards, the taxonomic status of the accessions was verified through analysis of seed characteristics, the variety names were checked for synonyms, and the passport data were complemented as much as possible. Subsequent collection management focuses on improving the composition of the collection in order to represent the genetic variation found in cultivated lettuce (Lactuca sativa) and its wild relatives.

The collection is regularly improved by uptake of a selection of the most important cultivars released during a five-year time period in the Netherlands and abroad, based on feedback from crop experts. The collection is also expanded through expeditions in order to collect wild relatives of lettuce. The exchange of wild Lactuca samples from other genebanks and institutes is another way to enhance the composition of the collection. The collection also frequently undergoes rationalisation to help remove redundant germplasm and non-authentic varieties based on analysis of passport, molecular, and morphological data.

Nowadays, the collection comprises over 2,500 accessions consisting of cultivars, landraces, research material, and samples of wild species. The cultivated lettuce accessions are classified as one of seven generally recognised horticultural types, i.e. butterhead, cos, crisp, cutting, latin, stalk, and oilseed lettuce. These accessions mainly originate from Europe, except for crisp lettuce (USA), stalk lettuce (China), and oilseed lettuce (Egypt). Wild species are predominantly represented by L. serriola, L. saligna, and L. virosa, which mainly originate from Europe and Asia.

Some collecting expeditions were specifically organized to collect wild relatives of lettuce, but these species have also frequently been collected opportunistically during other collecting activities. The earliest collecting expedition for lettuce took place in Israel in 1977. Afterwards, many other expeditions followed, such as IPGRI-funded expeditions to Egypt, collecting missions to Turkey, Daghestan (Russia), Armenia, and Georgia in the framework of the German-Dutch cooperation in Plant Genetic Resources, and collecting expeditions to Uzbekistan in cooperation with the Uzbekistan Research Institute of Plant Industry and the Vavilov Institute in Russia. More recently, collecting expeditions for wild relatives were organised in Armenia and Azerbaijan (2013), Jordan (2017), and Uzbekistan (2019).

More information regarding the collecting expeditions can be found here.

Lettuce accessions are regenerated in case of insufficient seed viability or nearly depleted seed stocks. Most lettuce accessions are regenerated under controlled greenhouse conditions. Cultivated lettuce and most wild relatives are self-fertilising, hence no protective measures are used to avoid cross-pollination, with the exception of a few outcrossing species. Regenerations are carried out in close cooperation with lettuce breeding companies affiliated with the Dutch association for the plant reproduction material sector (Plantum NL). More detailed information about regeneration procedures can be accessed through the link provided in the right margin of this page.

The lettuce collection is characterized both morphologically and molecularly. Accessions of cultivated material are described for over 20 morphological features, including seed traits and plant characteristics recorded during field trials. Accessions of wild species are described for nine morphological characters during greenhouse regeneration. All characterisation data are made available online and in downloadable files on CGN’s website.

Within the framework of the European Union project ‘Molecular markers for gene banks’, CGN’s entire lettuce collection, which at the time of tissue sampling in 1997 consisted of 2,323 accessions, was characterised with microsatellites and AFLPs (van Hintum, 2003; Jansen et al., 2006). The obtained molecular data have been used for various purposes, including studies on core collection strategies, acquisition protocol improvement for modern varieties, molecular biogeography of L. serriola (van de Wiel et al., 2010), collection redundancy reduction, and cultivar authenticity.

In addition to microsatellites and AFLPs, molecular data were also generated with SSAP, SRAP, TRAP, and NBS-DP markers for a selected set of 80 accessions in order to compare the ability of the marker technologies to describe genetic diversity in the collection (van Treuren & van Hintum, 2009). More recently, plants from 150 accessions were described for over 2,000 secondary metabolites (van Treuren et al., 2018). DNA resequencing data are currently being generated for the entire collection in cooperation with BGI (Shenzhen, China).

Users of CGN material are requested to donate their evaluation data to CGN after finalisation of the experiments, as part of the standard material transfer agreement. These data are processed by CGN, included in their information systems, and made publicly available on CGN’s website.

Evaluation programs are also carried out in close collaboration with lettuce breeding companies affiliated to the Dutch association for the plant reproduction material sector (Plantum NL). Data from such joint experiments can be exploited exclusively by the involved parties for an agreed time period (usually five years) before they are made publicly available by CGN. Most of the available evaluation data relate to resistances to pests and diseases, such as downy mildew (Bremia lactucae), powdery mildew (Erysiphe cichoracearum), leaf aphids (Macrosiphum euphorbiae, Nasonovia ribisnigri, and Uroleucon sonchi), root aphids (Pemphigus bursarius), lettuce drop (Sclerotinia sclerotiorum), and tomato spotted wilt virus (TSWV). Data are also available on chemical compounds such as nitrate, iron, and β-carotene.