Genetically modified plants, in the following referred to as genetically modified organisms or GMOs, have been commercially grown for almost two decades. In 2010 approximately 10% of the total global crop acreage was planted with GMOs (James, 2011). More than 30 countries have been growing commercial GMOs, and many more have performed field trials. Although the majority of commercial GMOs both in terms of acreage and specific events belong to the four species: soybean, maize, cotton and rapeseed, there are another 20+ species where GMOs are commercialized or in the pipeline for commercialization. The number of GMOs cultivated in field trials or for commercial production has constantly increased during this time period. So have the number of species, the number of countries involved, the diversity of novel (added) genetic elements and the global trade. All of these factors contribute to the increasing complexity of detecting and correctly identifying GMO derived material. Many jurisdictions, including the European Union (EU), legally distinguish between authorized (and therefore legal) and un-authorized (and therefore illegal) GMOs. Information about the developments, field trials, authorizations, cultivation, trade and observations made in the official GMO control laboratories in different countries around the world is often limited, despite several attempts such as the OECD BioTrack for voluntary dissemination of data. This lack of information inevitably makes it challenging to detect and identify GMOs, especially the un-authorized GMOs. The present paper reviews the state of the art technologies and approaches in light of coverage, practicability, sensitivity and limitations. Emphasis is put on exemplifying practical detection of un-authorized GMOs. Although this paper has a European (EU) bias when examples are given, the contents have global relevance.

Four real-time polymerase chain reaction systems aiming at the specific detection and quantification of maize DNA are described. They have been developed in four independent laboratories targeting different maize sequences, i.e., alcohol dehydrogenase (Adh1), high mobility group protein (hmga), invertase A (ivr1), and zein, respectively. They were all fully specific, showing a very similar quantification accuracy along a number of distantly related maize cultivars and being either single or low copy number genes. They were highly sensitive and exhibited limits of quantification below 100 maize genomic copies. In consequence, they are considered suitable for use as maize specific endogenous reference genes in DNA analyses, including GMO quantitative tests.

Using a sequenced pectate lyase-encoding gene (pel gene), we developed a PCR test for Erwinia carotovora. A set of primers allowed the amplification of a 434-bp fragment in E. carotovora strains. Among the 89 E. carotovora strains tested, only the Erwinia carotovora subsp. betavasculorum strains were not detected. A restriction fragment length polymorphism (RFLP) study was undertaken on the amplified fragment with seven endonucleases. The Sau3AI digestion pattern specifically identified the Erwinia carotovora subsp. atroseptica strains, and the whole set of data identified the Erwinia carotovora subsp. wasabiae strains. However, Erwinia carotovora subsp. carotovora and Erwinia carotovora subsp. odorifera could not be separated. Phenetic and phylogenic analyses of RFLP results showed E. carotovora subsp. atroseptica as a homogeneous group while E. carotovora subsp. carotovora and E. carotovora subsp. odorifera strains exhibited a genetic diversity that may result from a nonmonophyletic origin. The use of RFLP on amplified fragments in epidemiology and for diagnosis is discussed. Pectolytic erwinias cause diseases on a wide range of plants. The species Erwinia carotovora is divided into the four subspecies atroseptica, carotovora, betavasculorum, and wasabiae (13, 20). Erwinia carotovora subsp. betavasculorum and Erwinia carotovora subsp. wasabiae cause soft rot of sugar beet and Japanese horseradish, respectively (13, 37). Erwinia carotovora subsp. atroseptica is usually restricted to potato under cool temperate climate (27), while Erwinia carotovora subsp. carotovora seems to be more ubiquitous. Some strains, not isolated from potato, have been described as atypical E. carotovora subsp. atroseptica because they exhibit, for example, the ability to grow at 37°C (24, 29). A new subspecies called Erwinia carotovora subsp. odorifera was proposed for the atypical strains isolated from several hosts, including chicory, that produce odorous volatile metabolites (12). Because of their economic importance, we oriented our study on potato diseases. Symptoms on potato include blanking, blackleg, wilting, and soft rotting of aerial stem, tuber, and stolon end (28). E. carotovora subsp. atroseptica and E. carotovora subsp. carotovora cause these symptoms under certain