The French National Research Institute for Agriculture, Food and the Environment (INRAE) conserves and distributes five vegetable collections as seeds: the aubergine* (in this article the word aubergine refers to eggplant), pepper, tomato, melon and lettuce collections, together with their wild or cultivated relatives, are conserved in Avignon, France. Accessions from the collections have geographically diverse origins, are generally well-described and fixed for traits of agronomic or scientific interest and have available passport data. In addition to currently conserving over 10,000 accessions (between 900 and 3000 accessions per crop), the centre maintains scientific collections such as core collections and bi- or multi-parental populations, which have also been genotyped with SNP markers. Each collection has its own merits and highlights, which are discussed in this review: the aubergine collection is a rich source of crop wild relatives of Solanum; the pepper, melon and lettuce collections have been screened for resistance to plant pathogens, including viruses, fungi, oomycetes and insects; and the tomato collection has been at the heart of genome-wide association studies for fruit quality traits and environmental stress tolerance.

Pathogens that infect plants and animals use a diverse arsenal of effector proteins to suppress the host immune system and promote infection. Identification of effectors in pathogen genomes is foundational to understanding mechanisms of pathogenesis, for monitoring field pathogen populations, and for breeding disease resistance. We identified candidate effectors from the lettuce downy mildew pathogen Bremia lactucae by searching the predicted proteome for the WY domain, a structural fold found in effectors that has been implicated in immune suppression as well as effector recognition by host resistance proteins. We predicted 55 WY domain containing proteins in the genome of B . lactucae and found substantial variation in both sequence and domain architecture. These candidate effectors exhibit several characteristics of pathogen effectors, including an N-terminal signal peptide, lineage specificity, and expression during infection. Unexpectedly, only a minority of B . lactucae WY effectors contain the canonical N-terminal RXLR motif, which is a conserved feature in the majority of cytoplasmic effectors reported in Phytophthora spp. Functional analysis of 21 effectors containing WY domains revealed 11 that elicited cell death on wild accessions and domesticated lettuce lines containing resistance genes, indicative of recognition of these effectors by the host immune system. Only two of the 11 recognized effectors contained the canonical RXLR motif, suggesting that there has been an evolutionary divergence in sequence motifs between genera; this has major consequences for robust effector prediction in oomycete pathogens.

This work characterized mechanisms controlling cadmium (Cd) tolerance and accumulation in lettuce at both the physiological and genetic levels. These traits were evaluated in 18 Lactuca accessions representing a large genetic diversity. Cd tolerance and accumulation in roots and shoots as well as Cd translocation from roots to the shoot varied independently, and with a significant range of variation. Analyses of F1 progenies of crosses between cultivars with contrasted phenotypes showed that high tolerance to Cd, low Cd accumulation and low Cd root-shoot translocation were recessive traits. Results of analyses of F2 progenies of different crosses suggest that root Cd concentration and root-shoot Cd translocation were under a complex genetic determinism involving at least two loci. This work thus revealed that limiting both Cd accumulation and Cd root-shoot translocation in lettuce is possible and depends on recessive loci. Differences in the ability to accumulate Cd in roots in the long term could not be linked to differences in short-term 109Cd uptake into, or efflux from, roots. In contrast, the cultivar with the highest root-shoot Cd translocation was the same in the long term and in the short term, which suggests that this trait relies on processes that are implemented quickly (i.e. in less than three days) after the start of Cd exposure.

Bacterial leaf spot (BLS) is a disease that affects lettuce (Lactuca sativa L.) worldwide. The disease is caused by the bacterium Xanthomonas campestris pathovar vitians (Xcv), which exclusively infects lettuce and is particularly devastating in warm humid climates. Reine des Glaces (RG), an old Batavia-type cultivar, exhibited an uninvestigated partial resistance to Xcv. Quantitative trait loci (QTLs) were analyzed using two recombinant inbred line (RIL) populations derived from RG × Eruption and RG × Delsay using three isolates collected in California and Canada, each representing a different race, and an isolate collected in France. A major QTL was identified in linkage group 2 in both populations; additional, minor QTLs were also detected in other linkage groups. The major QTL collocates with the Xanthomonas resistance 1 (Xar1) and Xanthomonas campestris vitians resistance (Xcvr) genes that had previously been identified using RIL populations derived from Salinas 88 × La Brillante and PI 358001-1 × Tall Guzmaine. RG provides another resistance resource for combating BLS using data provided by this study for marker-assisted selection.

La lutte chimique preventive est encore aujourd’hui le principal moyen de lutte contre les bioagresseurs en culture de laitue d’hiver sous abri. Des strategies alternatives ont ete explorees dans le projet LILLA, visant soit a fournir des references experimentales manquantes sur des techniques non chimiques de protection des plantes, soit a tester des conduites de cultures basees sur des strategies integrees de protection, limitant le recours aux pesticides. Des leviers innovants, comme une resistance genetique accrue aux agents de la pourriture du collet, ou la conduite de l’irrigation en goutte a goutte au lieu de l’aspersion, ont pu etre identifies. En considerant un ensemble de 23 essais comparatifs de conduite des cultures, une diminution de moitie du nombre de traitements fongicides en association avec des techniques alternatives ne montre pas une augmentation statistique du risque de perte de recolte. Contre les pucerons, les strategies de controle biologique testees restent a ameliorer. Le cout de mise en oeuvre des techniques alternatives est significatif mais, pour la plupart d’entre elles, reste modere. Les plus efficaces de ces techniques pourraient plus facilement etre mises en oeuvre dans les exploitations si les incertitudes sur les revenus de la recolte etaient moins grandes.

The single dominant gene Mo3 from accession PIVT1398 of Lactuca virosa was shown previously to confer resistance to all tested isolates of Lettuce mosaic virus (LMV; genus Potyvirus), including mo1‐resistance‐breaking isolates. Because accession PIVT1398 is also resistant to the recently described potyvirus lettuce Italian necrotic virus (LINV), this study checked whether the Mo3 resistance locus could be involved in resistance to LINV. Introgression lines of Mo3 into two different L. sativa genetic backgrounds (Girelle and Mantilia) were resistant to isolates LMV‐9, LMV‐13 and LINV‐Fr (a French isolate of LINV), whereas Girelle and Mantilia were susceptible to these virus isolates. The resistance reaction in inoculated leaves of the introgression lines varied from absence of symptoms and absence of virus detection for LMV‐9, to hypersensitive‐like necrotic lesions and low virus titres for LINV‐Fr and large necrotic lesions and relatively abundant virus detection for LMV‐13. At the systemic level, the resistance phenotype was growth stage‐dependent for LINV‐Fr and LMV‐13. Inoculation of ≥28‐days‐old plants led to absence of symptoms and no virus with the three tested potyvirus isolates in almost all plants. Inoculation of younger plants (≤22‐days‐old) led to chlorotic/necrotic lesions on some apical leaves with low virus titre in a varying proportion of plants with LINV‐Fr and on all plants with efficient virus detection with LMV‐13. These results show that the Mo3 gene, or a tightly linked locus, in L. virosa PIVT1398 controls resistance to LINV in addition to LMV and could be used to breed L. sativa cultivars with broad‐spectrum potyvirus resistance.

Several potyviruses affect lettuce (Lactuca sativa) and chicory (Cichorium spp.) crops worldwide and are important constraints for production because of the direct losses that they induce and/or because of their seed transmission. Here, the molecular and biological properties are described of two potyviruses that were recently isolated from lettuce plants showing mosaic or strong necrotic symptoms in an experimental field in southeastern France. The first potyvirus belongs to the species Endive necrotic mosaic virus and is present in a large number of wild plant species, especially Tragopogon pratensis. It is unable to infect lettuce cultivars with a resistance to Turnip mosaic virus that is present in many European cultivars and probably conferred by the Tu gene. The second potyvirus belongs to the tentative species lettuce Italian necrotic virus and was not observed in wild plants. It infected all tested lettuce cultivars. Wild accessions of Lactuca serriola, Lactuca saligna, Lactuca virosa and Lactuca perennis were identified as resistant to one or the other potyvirus and could be used for resistance breeding in lettuce. No resistance against these two potyviruses was observed in the tested Cichorium endivia cultivars. In contrast, all tested Cichorium intybus cultivars or accessions were resistant.

Lettuce downy mildew caused by Bremia lactucae is the most important disease of lettuce worldwide. Breeding for resistance to this disease is a major priority for most lettuce breeding programs. Many genes and factors for resistance to B. lactucae have been reported by multiple researchers over the past ~50 years. Their nomenclature has not been coordinated, resulting in duplications and gaps in nominations. We have reviewed the available information and rationalized it into 51 resistance genes and factors and 15 quantitative trait loci along with supporting documentation as well as genetic and molecular information. This involved multiple rounds of consultation with many of the original authors. This paper provides the foundation for naming additional genes for resistance to B. lactucae in the future as well as for deploying genes to provide more durable resistance.

Agricultural intensification has increased crop productivity but decreased agroecosystem services. Agricultural intensification is occurring notably for horticultural crops such as lettuce. In conventional agriculture, lettuce protection is achieved mostly by preventive applications of pesticides with about eight treatments for a 60–90-day-long cycle in the Mediterranean region. However, new sustainable control strategies are needed due to pesticide impact on environment and human health, emerging pesticide resistance, and stricter policies on levels of pesticide residues in food. Here, we review knowledge and methods allowing to grow lettuce with less pesticides. Advances shown are based on pest ecology and pathogen control by the agroecosystem. The major points are as follows: (1) pest and pathogen community composition depends partly on climatic conditions. The identification of pests and pathogens that can threaten the crop is the first step to design innovative lettuce cropping systems less dependent on pesticides. (2) The numerous alternative techniques currently available should be combined to control lettuce pests and pathogens. The effects of alternative techniques on non-target organisms including non-target pests are poorly known so far. (3) Designing sustainable systems requires taking into account ecological interactions and suitability of different management techniques of low impact.

L'adaptation, a la laitue, de la mutagenese par exposition aux UV de protoplastes a permis de selectionner des colonies cellulaires resistantes au chlorsulfuron, puis de regenerer des plantes resistantes. L'analyse genetique des plantes a montre que les trois mutants regeneres possedent la meme mutation

La conservation et la connaissance des ressources genetiques d'especes vegetales cultivees : un enjeu pour l'agriculture et un defi pour les acteurs