Joel Allainguillaume

A direct regional scale estimate of transgene movement from genetically modified oilseed rape to its wild progenitors

One of the major environmental concerns over genetically modified (GM) crops relates to transgene movement into wild relatives. The pattern of hybridization ultimately affects the scale and rapidity of ecological change and the feasibility of containment. A new procedure for quantifying hybrid formation over large areas is described. Remote sensing was used to identify possible sites of sympatry between Brassica napus and its progenitor species across 15 000 km2 of south‐east England in 1998. Two sympatric populations with B. rapa and one with B. oleracea were found over the entire survey area. Every newly recruited plant in these populations in 1999 was screened for hybrid status using flow cytometry and molecular analyses. One hybrid was observed from the 505 plants screened in the B. rapa populations but none of the nine B. oleracea recruits were hybrids. Measures to minimize gene flow are suggested, and a procedure for the post‐release evaluation and containment of GM cultivars is proposed.

Fitness of hybrids between rapeseed (Brassica napus) and wild Brassica rapa in natural habitats

Fitness of hybrids between genetically modified (GM) crops and wild relatives influences the likelihood of ecological harm. We measured fitness components in spontaneous (non‐GM) rapeseed × Brassica rapa hybrids in natural populations. The F1 hybrids yielded 46.9% seed output of B. rapa, were 16.9% as effective as males on B. rapa and exhibited increased self‐pollination. Assuming 100% GM rapeseed cultivation, we conservatively predict < 7000 second‐generation transgenic hybrids annually in the United Kingdom (i.e. ∼20% of F1 hybrids). Conversely, whilst reduced hybrid fitness improves feasibility of bio‐containment, stage projection matrices suggests broad scope for some transgenes to offset this effect by enhancing fitness.

Spontaneous gene flow from rapeseed (Brassica napus) to wild Brassica oleracea

Research on the environmental risks of gene flow from genetically modified (GM) crops to wild relatives has traditionally emphasized recipients yielding most hybrids. For GM rapeseed (Brassica napus), interest has centred on the ‘frequently hybridizing’ Brassica rapa over relatives such as Brassica oleracea, where spontaneous hybrids are unreported in the wild. In two sites, where rapeseed and wild B. oleracea grow together, we used flow cytometry and crop-specific microsatellite markers to identify one triploid F1 hybrid, together with nine diploid and two near triploid introgressants. Given the newly discovered capacity for spontaneous introgression into B. oleracea, we then surveyed associated flora and fauna to evaluate the capacity of both recipients to harm cohabitant species with acknowledged conservational importance. Only B. oleracea occupies rich communities containing species afforded legislative protection; these include one rare micromoth species that feeds on B. oleracea and warrants further assessment. We conclude that increased attention should now focus on B. oleracea and similar species that yield few crop-hybrids, but possess scope to affect rare or endangered associates.

Rapeseed cytoplasm gives advantage in wild relatives and complicates genetically modified crop biocontainment

Biocontainment methods for genetically modified crops closest to commercial reality (chloroplast transformation, male sterility) would be compromised (in absolute terms) by seed-mediated gene flow leading to chloroplast capture. Even in these circumstances, however, it can be argued that biocontainment still represses transgene movement, with the efficacy depending on the relative frequency of seed- and pollen-mediated gene flow. In this study, we screened for crop-specific chloroplast markers from rapeseed (Brassica napus) amongst sympatric and allopatric populations of wild B. oleracea in natural cliff-top populations and B. rapa in riverside and weedy populations. We found only modest crop chloroplast presence in wild B. oleracea and in weedy B. rapa, but a surprisingly high incidence in sympatric (but not in allopatric) riverside B. rapa populations. Chloroplast inheritance models indicate that elevated crop chloroplast acquisition is best explained if crop cytoplasm confers selective advantage in riverside B. rapa populations. Our results therefore imply that chloroplast transformation may slow transgene recruitment in two settings, but actually accelerate transgene spread in a third. This finding suggests that the appropriateness of chloroplast transformation for biocontainment policy depends on both context and geographical location.

Quantifying gene movement from oilseed rape to its wild relatives using remote sensing

The potential environmental risks due to gene flow from genetically modified (GM) crops into wild plant populations are currently of great concern. Of particular interest is gene flow from GM oilseed rape (Brassica napus) into its wild parental species B. rapa and B. oleracea, with which it forms spontaneous hybrids. The rate of hybridization is best determined empirically under a wide variety of field conditions. A procedure for quantifying hybrid formation using remote sensing over a large area of southern England is described. Satellite sensor images were used to identify localities where gene flow was most likely by searching for oilseed rape fields adjacent to regions where the parent plants occur, namely rivers and cliff-tops. These sites were visited and screened for hybrids. A single hybrid was observed in an area of over 16 000 km2. We use these data to suggest a strategy to minimise gene flow following commercial scale release of GM B. napus across Europe and propose a procedure that may allow post-release containment.

Use of airborne remote sensing to detect riverside Brassica rapa to aid in risk assessment of transgenic crops

High resolution descriptions of plant distribution have utility for many ecological applications but are especially useful for predictive modeling of gene flow from transgenic crops. Difficulty lies in the extrapolation errors that occur when limited ground survey data are scaled up to the landscape or national level. This problem is epitomized by the wide confidence limits generated in a previous attempt to describe the national abundance of riverside Brassica rapa (a wild relative of cultivated rapeseed) across the United Kingdom. Here, we assess the value of airborne remote sensing to locate B. rapa over large areas and so reduce the need for extrapolation. We describe results from flights over the river Nene in England acquired using Airborne Thematic Mapper (ATM) and Compact Airborne Spectrographic Imager (CASI) imagery, together with ground truth data. It proved possible to detect 97% of flowering B. rapa on the basis of spectral profiles. This included all stands of plants that occupied >2m square (>5 plants), which were detected using single-pixel classification. It also included very small populations (<5 flowering plants, 1-2m square) that generated mixed pixels, which were detected using spectral unmixing. The high detection accuracy for flowering B. rapa was coupled with a rather large false positive rate (43%). The latter could be reduced by using the image detections to target fieldwork to confirm species identity, or by acquiring additional remote sensing data such as laser altimetry or multitemporal imagery.

Genome engineering for pest resistance in potato

The potato (Solanum tuberosum L.) is susceptible to many pests and diseases. There are over 200 wild relatives, many of which contain useful resistance genes. These species have been poorly utilised in potato breeding, largely because of hybridization barriers and the need for extensive backcrossing to restore agronomic performance. Two strategies to overcome these difficulties are explored. The first uses a mechanism apparently unique to the Solanaceae. Pollination of tetraploid Solanum tuberosum using pollen from diploid Solanum species (usually S. phureja) occasionally produce offspring with a diploid chromosome number (2n = 2x = 24). These plants are known as dihaploids. Dihaploids are largely maternal in origin but also contain a small amount of genetic material from the male (dihaploid inducer) parent. There are several species capable of producing dihaploid offspring. Many of these also contain desirable resistance genes. Successful exploitation of this natural introgression event partly depends on the amount of DNA transferred from the male parent. Markers generated by ISSR-PCR, RAPD and RFLP analyses are used to estimate the genetic contribution made by the male parent. Variation is observed between female (S. tuberosum) clones but most dihaploids were found to possess fewer than 8% of markers specific to the male parent. It is suggested that the production of resistant dihaploid inducers from several wild species could be incorporated into a dihaploid-based breeding programme. The second strategy seeks to exploit chromosome instability in callus culture. Hexaploid and aneuploid somatic hybrids between S. tuberosum and S. sanctae-rosae were compared on the basis of ISSR band profiles and morphology. It is inferred that the aneuploid had probably lost chromosomes from both parents but predominantly from S. sanctaerosae. Both somatic hybrids were subjected to further regeneration through callus culture and some were found to lose ISSR bands. Principal Component Analysis of tuber characters suggested that secondary regenerants formed a continuum of variation connecting the two parents. Some individuals were found to possess tubers within the range of variation of each parent although all ISSR-PCR profiles examined differed from those of the parents. The limitations and commercial potential of each strategy are discussed.