Pollen-Mediated Movement of Herbicide Resistance Between Commercial Canola Fields (original) (raw)
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Predicting the Spread of Herbicide Resistance in Australian Canola Fields
Transgenic Research, 2003
A common concern expressed about the commercial release of transgenic canola into cropping systems is the risks of unwanted gene flow between varieties. Experimental data is emerging that answers some of the theoretical questions that have been posed when considering gene flow on a landscape scale. This study developed models that utilise some of this published data in an attempt to quantify the spread of transgenes in a commercial farming system. The models, which included bootstrapping the empirical data and three mathematical simulations, were compared with each other and the published data. One of the mathematical models estimated average resistance frequency by imposing a Poisson distribution around the published mean value for a single transgenic field surrounded by conventional canola fields and the other two were derived from the theory that pollen flow decreased with distance in the form of a log decay curve. The predictions of all models suggested that the average frequency of resistance occurring from pollen flow in neighbouring canola fields, even when multiple transgenic fields are adjacent to the conventional fields, are likely to be below the current internationally accepted thresholds for contamination.
The Establishment of Genetically Engineered Canola Populations in the U.S
PLoS ONE, 2011
Concerns regarding the commercial release of genetically engineered (GE) crops include naturalization, introgression to sexually compatible relatives and the transfer of beneficial traits to native and weedy species through hybridization. To date there have been few documented reports of escape leading some researchers to question the environmental risks of biotech products. In this study we conducted a systematic roadside survey of canola (Brassica napus) populations growing outside of cultivation in North Dakota, USA, the dominant canola growing region in the U.S. We document the presence of two escaped, transgenic genotypes, as well as non-GE canola, and provide evidence of novel combinations of transgenic forms in the wild. Our results demonstrate that feral populations are large and widespread. Moreover, flowering times of escaped populations, as well as the fertile condition of the majority of collections suggest that these populations are established and persistent outside of cultivation.
Field Crops Research, 2007
Australian canola breeders have successfully improved blackleg resistance, seed oil and meal quality and local adaptation of oilseed rape (Brassica napus) from 1970 to 2000 in five breeding cycles, averaging 6 years/cycle, in a closed population. The 18 ancestral varieties in 1970 included 16 B. napus from Canada, Europe and Asia and 2 B. juncea varieties. Introductions with improved seed quality were generally very susceptible to blackleg under Australian conditions. Of the varieties released from 1995 to 2002, 11 ancestral varieties contributed 98.7% of the pedigree composition, and 2 ancestors (Canadian low erucic spring variety Zephyr, and Polish low glucosinolate spring variety Bronowski) were present in the pedigrees of every variety. Approximately half of the ancestral contribution was from Asian B. napus or B. juncea, and half from European or Canadian B. napus. Assuming an effective population size of 11, the inbreeding coefficient of the population at the end of the fifth cycle was 0.21, which represents 21% cumulative loss of alleles through random genetic drift. The coefficients of ancestry among four varieties released from 1996 to 2002 ranged from 0.127 to 0.371. While the original parents were very diverse, the population is showing signs of loss of genetic diversity that will impact on future breeding progress. There has been a slow decay in polygenic blackleg resistance (average À0.15 resistance units per year) which, so far, has been countered by a net genetic improvement rate of approximately +0.13 resistance units per year over 30 years. New genetic diversity should be introduced to maintain a positive net improvement rate in blackleg resistance, or for adaptation to low rainfall environments. New technologies such as doubled haploidy may improve the efficiency of selection for earliness and other polygenic characters, and accelerate cycles of selection. Major challenges exist for Australian canola breeders to introgress new genetic diversity and increase effective population size, while retaining genetic gains made over the past 30 years. Similar challenges face most crop breeders who are attempting to improve their crop in the face of changing future environments. #
Review Gene flow from glyphosate-resistant crops
2008
Gene flow from transgenic glyphosate-resistant crops can result in the adventitious presence of the transgene, which may negatively impact markets. Gene flow can also produce glyphosate-resistant plants that may interfere with weed management systems. The objective of this article is to review the gene flow literature as it pertains to glyphosate-resistant crops. Gene flow is a natural phenomenon not unique to transgenic crops and can occur via pollen, seed and, in some cases, vegetative propagules. Gene flow via pollen can occur in all crops, even those that are considered to be self-pollinated, because all have low levels of outcrossing. Gene flow via seed or vegetative propagules occurs when they are moved naturally or by humans during crop production and commercialization. There are many factors that influence gene flow; therefore, it is difficult to prevent or predict. Gene flow via pollen and seed from glyphosate-resistant canola and creeping bentgrass fields has been document...
Gene flow from glyphosate-resistant crops
Pest Management Science, 2008
Gene flow from transgenic glyphosate-resistant crops can result in the adventitious presence of the transgene, which may negatively impact markets. Gene flow can also produce glyphosate-resistant plants that may interfere with weed management systems. The objective of this article is to review the gene flow literature as it pertains to glyphosate-resistant crops. Gene flow is a natural phenomenon not unique to transgenic crops and can occur via pollen, seed and, in some cases, vegetative propagules. Gene flow via pollen can occur in all crops, even those that are considered to be self-pollinated, because all have low levels of outcrossing. Gene flow via seed or vegetative propagules occurs when they are moved naturally or by humans during crop production and commercialization. There are many factors that influence gene flow; therefore, it is difficult to prevent or predict. Gene flow via pollen and seed from glyphosate-resistant canola and creeping bentgrass fields has been documented. The adventitious presence of the transgene responsible for glyphosate resistance has been found in commercial seed lots of canola, corn and soybeans. In general, the glyphosate-resistant trait is not considered to provide an ecological advantage. However, regulators should consider the examples of gene flow from glyphosate-resistant crops when formulating rules for the release of crops with traits that could negatively impact the environment or human health.
A study of crop-to-crop gene flow using farm scale sites of fodder maize (Zea mays L.) in the UK
Transgenic Research, 2008
From 2000 to 2003 a range of Farm Scale Evaluation (FSE) trials were established in the UK to assess the effect of the release and management of herbicide tolerant (HT) crops on arable weeds and invertebrates. The FSE trials for maize were also used to investigate crop-to-crop gene flow and to develop a statistical model for the prediction of gene flow frequency that can be used to evaluate current separation distance guidelines for GM crops. Seed samples were collected from the non-GM half of 55 trial sites and 1,055 were tested for evidence of gene flow from the GM HT halves using a quantitative PCR assay specific to the HT (pat) gene. Rates of gene flow were found to decrease rapidly with increasing distance from the GM source. Gene flow was detected in 30% of the samples (40 out of 135) at 150 m from the GM source and events of GM to non-GM gene flow were detected at distances up to and including 200 m from the GM source. The quantitative data were subjected to statistical analysis and a two-step model was found to provide the best fit for the data. A dynamic whole field model predicted that a square field (150 m · 150 m in size) of grain maize would require a separation distance of 3 m for the adjacent crop to be below a 0.9% threshold (with < 2% probability of exceeding the threshold). The data and models presented here are discussed in the context of necessary separation distances to achieve various possible thresholds for adventitious presence of GM in maize.
Environmental Costs and Benefits of Transgenic Crops, 2005
The public concern about the impact of genetically modified crops on the natural environment triggered a steady stream of research during the last decade. Among the possible impacts, the 'escape' of the transgene, either through dispersal of the crop plant outside the agricultural area or through hybridization with wild relatives, attracted a lot of attention, in particular in relation to the possibility of increasing 'weediness'. For gene flow through hybridization to occur, pollen grains must achieve fertilization and seeds must germinate and produce sexually mature plants. Subsequently, the first generation hybrids should be sufficiently fit to survive to sexual maturity and thus produce follow-up generations by which actual introgression into wild acceptor-species genomes could occur through repeated backcrossing. All these steps are reviewed in this paper. It will become evident that, in order to estimate a transgene's capacity to introgress and persist in wild relatives, all steps in the introgression process should be considered. Areas where still relatively little definite data has been published are i) assessing the extent to which genes, such as those conferring resistance to biotic as well as abiotic stresses, indeed enhance fitness in natural settings and the consequences of introgression of these for these environments; and ii) improving this assessment of fitness, e.g. by not only scoring relevant traits, such as those related to fecundity, but also monitoring them in realistic field situations. In this regard, more data on, for instance, the effects of the transgene insertion site on the introgression process and the importance of fitness of the intermediate stages (backcrosses) would be needed to reach a more general insight. In relation to co-existence of GMO and organic agriculture, crop-to-crop gene flow also needs to be controlled. Therefore, a wide variety of possible hybridization barriers, both physical and biological, are discussed. The technical limitations of assessing introgression from crop to wild avoiding the use of transgenic markers are discussed on the basis of work on lettuce.
Biology & Environment: Proceedings of the Royal Irish Academy, 2012
Although now we have had many years of research completed on assessing the potential environmental impact of GM crops, concern remains over their potential impact on biodiversity in the rural landscape. In particular, issues have arisen in regards to the modification of crops with traits that could introgress into sexually compatible wild relatives. In contrast to wheat, barley, potato and maize, Brassica napus (oilseed rape) is the only commercial crop grown in Ireland at present with the potential to successfully transfer its DNA, via pollen-mediated gene flow, into interrelated weed species. This review details the species in question and by examining the relevant literature that relates to Irish agronomic conditions, demonstrates that gene flow is likely to occur, especially to an earlier used cultivar, Brassica rapa. However, the critical factor remains not that GM traits will flow from the commercial source but what might the consequences of said gene flow events be. This review indicates that the conferred trait in question (in this case, herbicide tolerance) can only impact on weed diversity in the presence of selecting herbicide action. In the absence of the herbicide, the GM traits will be lost from the wild species over time and will not confer any selective advantage that could facilitate population growth.
Gene Flow from Herbicide-Resistant Crops: Itʼs Not Just for Transgenes
Journal of Agricultural and Food Chemistry, 2011
Gene flow was raised as one of the first issues related to the development and release of genetically engineered (GE) crops. Gene flow has remained a topic of discussion for more than 20 years and is still used as an argument against the release of transgenic crops. With respect to herbicide-resistant crops, gene flow does not differ whether the herbicide resistance trait is introduced via genetic engineering or via conventional breeding techniques. Conventional breeding and genetic engineering techniques have been used to produce herbicide resistance in many of the same crop species. In addition, conventional breeding has been used to produce a broader range of herbicide-resistant crops than have been genetically engineered for herbicide resistance. Economic, political, and social concerns center on the breeding technique, but the results of gene flow for weed management are the same irrespective of breeding technique. This paper will focus on gene flow from nonGE herbicide-resistant crops in North America.
Biology and Environment: Proceedings of the Royal Irish Academy, 2011
Although now we have had many years of research completed on assessing the potential environmental impact of GM crops, concern remains over their potential impact on biodiversity in the rural landscape. In particular, issues have arisen in regards to the modification of crops with traits that could introgress into sexually compatible wild relatives. In contrast to wheat, barley, potato and maize, Brassica napus (oilseed rape) is the only commercial crop grown in Ireland at present with the potential to successfully transfer its DNA, via pollen-mediated gene flow, into inter-related weed species. This review details the species in question and by examining the relevant literature that relates to Irish agronomic conditions, demonstrates that gene flow is likely to occur, especially to an earlier used cultivar, Brassica rapa. However, the critical factor remains not that GM traits will flow from the commercial source but what might the consequences of said gene flow events be. This review indicates that the conferred trait in question (in this case, herbicide tolerance) can only impact on weed diversity in the presence of selecting herbicide action. In the absence of the herbicide, the GM traits will be lost from the wild species over could facilitate population growth.