Molecular and biological characterization of two potyviruses infecting lettuce in southeastern France

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.     

Cucumber mosaic virus populations in Tunisian pepper crops are mainly composed of virus reassortants with resistance‐breaking properties

Cucumber mosaic virus is one of the most prevalent viruses in Tunisian pepper crops, where it has been detected in 68% of plants developing mosaic symptoms, making it essential to characterize the molecular and biological properties of local CMV populations. Two hundred and seventy‐eight isolates collected in the late 1990s, 2006 and 2008–2010 were characterized genetically. Isolates belonging to the three phylogenetic subgroups of CMV (IA, IB and II) were detected, but surprisingly, 90% of the isolates were reassortants between subgroups IA and IB, with two predominant haplotypes, IB‐IA‐IA and IB‐IA‐IB (nomenclature according to the subgrouping of the three genomic RNAs). The IB‐IA‐IA haplotype was present in all regions surveyed, while IB‐IA‐IB was observed only in northern Tunisia. This situation was unexpected, because CMV reassortants were previously thought to be counterselected in nature, and this raises the questions of the origin of IB strains in Tunisia and of the widespread distribution of these two reassortant types. Phylogenetic studies revealed low diversity within haplotypes, whatever the locality or the year of sampling. However, analysis of haplotype frequencies revealed a high genetic differentiation between CMV populations, which was better explained by the localities of sampling than by years. Geographic distances affected the differentiation of CMV populations, mainly between north and central Tunisia. When tested against a polygenic resistance to CMV movement in pepper, 55 of 57 isolates tested were able to break the resistance, indicating that this resistance would not be useful for controlling CMV in Tunisian pepper fields.     

An overview of general features of risk assessments of genetically modified crops

The intentional introduction into the environment or market of genetically modified organisms (GMOs) is nearly always governed by a framework of science-based risk assessment and risk management measures. This is usually implemented through the integration of hazard identification and characterisation of all of the elements of risk associated with a new GM crop or derived product. Typical categories of hazards arising from the introduction of transgenic crops include: possible unintended negative health effects in a susceptible subgroup of the consumer (target) population; the evolution of resistance in the targeted pest/pathogen populations when the transgene confers resistance to a pest or pathogen; non-target hazards associated directly or indirectly with the transgenic plant or transgene product outside the plant; and those associated with the integration and subsequent expression of the transgene in a different organism or species following gene flow. The consequences of likely exposure to these and other hazards are considered in this introduction to the main issues raised when evaluating the possible risks arising from the importation or cultivation of genetically modified crops.     

The permeability of plant cell walls as measured by gel filtration chromatography

The permeability of plant cell walls to macromolecules may limit the ability of enzymes to alter the biochemical and physical properties of the wall. Proteins of molecular weight up to 60,000 can permeate a substantial portion of the cell wall. Measurements of wall permeability in which cells are exposed to hypertonic solutions of macromolecules may seriously underestimate wall permeability.