Assessment of real-time PCR based methods for quantification of pollen-mediated gene flow from GM to conventional maize in a field study

Application of the maximum threshold distances to reduce gene flow frequency in the coexistence between genetically modified (GM) and non-GM maize

On the coexistence of genetically modified (GM) and non-GM maize, the isolation distance plays an important role in controlling the transgenic flow. In this study, maize gene flow model was used to quantify the MTD0.1% and MTD1% in the main maize-planting regions of China; those were the maximum threshold distance for the gene flow frequency equal to or lower than 1% and 0.1%. The model showed that the extreme MTD1% and MTD0.1% were 187 and 548 m, respectively. The regions of northern China and the coastal plain, including Hainan crop winter-season multiplication base, showed a significantly high risk for maize gene flow, while the west-south of China was the largest low-risk areas. Except for a few sites, the isolation distance of 500 m could yield a seed purity of better than 0.1% and meet the production needs of breeder seeds. The parameters of genetic competitiveness (cp) were introduced to assess the effects of hybrid compatibility between the donor and recipient. The results showed that hybrid incompatibility could minimize the risk. When cp = 0.05, MTD1% and MTD0.1% could be greatly reduced within 19 m and 75 m. These data were helpful to provide scientific data to set the isolation distance between GM and non-GM maize and select the right place to produce the hybrid maize seeds.

Effectiveness of different sampling schemes in predicting adventitious genetically modified maize content in a smallholder farming system

When genetically modified (GM) maize is planted in an open field, it may cross-pollinate with the nearby non-GM maize under certain airflow conditions. Suitable sampling methods are crucial for tracing adventitious GM content. By using field data and bootstrap simulation, we evaluated the performance of common sampling schemes to determine the adventitious GM content in small maize fields in Taiwan. A pollen dispersal model that considered the effect of field borders, which are common in Asian agricultural landscapes, was used to predict the cross-pollination (CP) rate. For the 2009-1 field data, the six-transect (T_six), JM method for low expected flow (JM[L]), JM method for high expected flow (JM[H]), and V-shaped transect (T_V) methods performed comparably to simple random sampling (SRS). T_six, T_V, JM(L), and JM(H) required only 13% or less of the sample size required by SRS. After the simulation and verification of the 2009-2 and 2010-1 field data, we concluded that T_six, T_V, JM(L), and systematic random sampling methods performed equally as well as SRS in CP rate predictions. Our findings can serve as a reference for monitoring the pollen dispersal tendencies of maize in countries with smallholder farming systems.

A new isolation device for shortening gene flow distance in small-scale transgenic maize breeding

The transmission of pollen is the main cause of maize gene flow. Under the compulsory labeling system for genetically modified (GM) products in China, isolation measures are crucial. At present, there is no effective isolation device for preventing and controlling the short-range flow of GM maize pollen. The purposes of the present experiments were to overcome the deficiencies of existing technology and to demonstrate a new isolation device for decreasing the gene flow distance of GM maize. The isolation device we invented was shown to be more robust than traditional isolation methods, and it can be disassembled and repeatedly reused. The most important point was that the frequency of gene flow could be greatly reduced using this device. When the distance from the isolation device was more than 1 m, the gene flow rate could be decreased to less than 1%, and when the distance from the isolation device was more than 10 m, the gene flow rate could be reduced to less than 0.1%. When the isolation device was adopted to isolate GM maize in conjunction with bagging the tassels of GM maize at the pollination stage, the gene flow could be controlled to less than 0.1% when the distance from the isolation device was more than 1 m. This device was, however, only applicable for small plots and can shorten the isolation distance of GM maize planting and improve the purity of seeds, all while meeting the needs of close isolation breeding. The use of this device represents a feasible method for risk prevention and control of GM crops.

Increased pollen source area does not always enhance the risk of pollen dispersal and gene flow in Oryza sativa L

Pollen dispersal is one of the main ways of gene flow. In the past years, rice pollen dispersal and gene flow have been well studies. However, there is much dispute whether the risk of pollen dispersal and gene flow continuously increases with the source area. A Lagrangian stochastic model was used to simulate the pollen depositions at different distances from different pollen source areas. The field experiments showed a good fit in the pollen depositions. The larger the source area, the more the pollen grains were deposited at each distance, with the pollen dispersal distance increasing accordingly. However, this effect gradually leveled off as the source area increased. In the large-area of pollen source, we found a significantly higher saturation point for the amount of pollen deposition. Once the source area exceeded 1000 × 1000 m2, the pollen deposition no longer increased, even if the source area continued to increase, indicating the "critical source area" of rice pollen dispersal. However, a 100 × 100 m2 critical source area for conventional rice and hybrid rice was sufficient, while the critical source area for the sterile line was about 230 × 230 m2.

Intercrops can mitigate pollen-mediated gene flow from transgenic cotton while simultaneously reducing pest densities

Genetically modified (GM) cotton, engineered to express Bt toxins that protect it from insect damage, has become the most successfully commercialized GM crop in China since its authorization in 1997. In light of the potential ecological consequences of pollen-mediated gene flow (PGF) from GM plants, a two year field trial was conducted to test the effects on PGF of sunflower, Helianthus annuus, buckwheat, Fagopyrum esculentum, and soybean, Glycine max, as intercrops in non-GM cotton fields during 2017 and 2018. DNA tests for hybridized seed were used to estimate rates of PGF in intercrop treatments. PGF was the lowest in cotton intercropped with either buckwheat or sunflower, likely due to the trapping of pollen in these flowers, and/or the diversion of pollinators away from cotton flowers. PGF declined as an exponential function of distance from the GM cotton; Y = -lnx was the model of best fit for estimating pollen dispersal potential. A sunflower intercrop reduced the peak abundance of Aphis gossypii, (Hemiptera: Aphididae), Bemisia tabaci (Hemiptera: Aleyrodidae), and Nysius ericae (Hemiptera: Lygaeidae) on cotton plants, although densities of Tetranychus cinnabarinus (Acari: Tetranychidae), were increased. A buckwheat intercrop had very similar effects on these pests, likely due to attraction of their natural enemies. We conclude that sunflower and buckwheat are suitable intercrops for reducing PGF from GM cotton, and may be useful for reducing PGF from other insect-pollinated GM crops in the agricultural landscape, while simultaneously contributing to control of specific pests. This is the first demonstration, to our knowledge, that intercrops can be used to reduce PGF from transgenic plants.

Pollen-mediated gene flow from transgenic cotton is constrained by physical isolation measures

The public concern about pollen-mediated gene flow (PGF) from genetically modified (GM) crops to non-GM crops heats up in recent years over China. In the current study, we conducted greenhouse and field experiments to measure PGF with various physical isolation measures, including 90, 80, 60 and 40 holes/cm² separation nets and Sorghum bicolor, Zea mays and Lycopersicon esculentum separation crops between GM cotton and non-GM line (Shiyuan321) by seed DNA test during 2013 to 2015, and pollen grain dyeing was also conducted to assess the pollen flow in greenhouse during 2013. Our results revealed that (1) PGF varied depending on the physical isolation measures. PGF was the lowest with 90 holes/cm² separation net and S. bicolor separation crop, and the highest with 40 holes/cm² separation net and no isolation measure. (2) Similar to PGF results, 90 holes/cm² separation net and S. bicolor separation crop could minimize the pollen dispersal. (3) PGF declined exponentially with increasing distance between GM cotton and Shiyuan321. Because of the production mode of farm household (limited cultivated area) in China, our study is particularly important, which is not only benefit for constraining PGF, but also has potential application value in practical production and the scientific researches.

Quantification of concentrated Chinese medicine granules by quantitative polymerase chain reaction

Determination of the amount of constituent in a multi-herb product is important for quality control. In concentrated Chinese medicine granules (CCMG), no dregs are left after dissolution of the CCMG. This study is the first to examine the feasibility of using quantitative polymerase chain reaction (qPCR) to find the amount of CCMG in solution form. DNA was extracted from Hirudo and Zaocys CCMG mixed at different ratios and amplified in qPCR using species-specific primers. The threshold cycle (C_T) obtained was compared with the respective standard curves. Results showed that reproducible quantification results could be obtained (1) for 5-50mg CCMG using a modified DNA extraction protocol, (2) amongst DNA extracted from the same batch of CCMG and (3) amongst different batches of CCMG from the same company. This study demonstrated the constitute amount of CCMG in a mixture could be determined using qPCR. This work has extended the application of DNA techniques for the quantification of herbal products and this approach may be developed for quality assurance in the CCMG industry.

Sampling Strategies for Evaluating the Rate of Adventitious Transgene Presence in Non-Genetically Modified Crop Fields

According to E.U. regulations, the maximum allowable rate of adventitious transgene presence in non-genetically modified (GM) crops is 0.9%. We compared four sampling methods for the detection of transgenic material in agricultural non-GM maize fields: random sampling, stratified sampling, random sampling + ratio reweighting, random sampling + regression reweighting. Random sampling involves simply sampling maize grains from different locations selected at random from the field concerned. The stratified and reweighting sampling methods make use of an auxiliary variable corresponding to the output of a gene-flow model (a zero-inflated Poisson model) simulating cross-pollination as a function of wind speed, wind direction, and distance to the closest GM maize field. With the stratified sampling method, an auxiliary variable is used to define several strata with contrasting transgene presence rates, and grains are then sampled at random from each stratum. With the two methods involving reweighting, grains are first sampled at random from various locations within the field, and the observations are then reweighted according to the auxiliary variable. Data collected from three maize fields were used to compare the four sampling methods, and the results were used to determine the extent to which transgene presence rate estimation was improved by the use of stratified and reweighting sampling methods. We found that transgene rate estimates were more accurate and that substantially smaller samples could be used with sampling strategies based on an auxiliary variable derived from a gene-flow model.

Modeling gene flow distribution within conventional fields and development of a simplified sampling method to quantify adventitious GM contents in maize

Genetically modified (GM) crops have been commercially grown for two decades. GM maize is one of 3 species with the highest acreage and specific events. Many countries established a mandatory labeling of products containing GM material, with thresholds for adventitious presence, to support consumers’ freedom of choice. In consequence, coexistence systems need to be introduced to facilitate commercial culture of GM and non-GM crops in the same agricultural area. On modeling adventitious GM cross-pollination distribution within maize fields, we deduced a simple equation to estimate overall GM contents (%GM) of conventional fields, irrespective of its shape and size, and with no previous information on possible GM pollen donor fields. A sampling strategy was designed and experimentally validated in 19 agricultural fields. With 9 samples, %GM quantification requires just one analytical GM determination while identification of the pollen source needs 9 additional analyses. A decision support tool is provided.

Pollen-mediated gene flow from transgenic cotton under greenhouse conditions is dependent on different pollinators

With the large-scale release of genetically modified (GM) crops, there are ecological concerns on transgene movement from GM crops to non-GM counterparts and wild relatives. In this research, we conducted greenhouse experiments to measure pollen-mediated gene flow (PGF) in the absence and presence of pollinators (Bombus ignitus, Apis mellifera and Pieris rapae) in one GM cotton (resistant to the insect Helicoverpa armigera and the herbicide glyphosate) and two non-GM lines (Shiyuan321 and Hai7124) during 2012 and 2013. Our results revealed that: (1) PGF varied depending on the pollinator species, and was highest with B. ignitus (10.83%) and lowest with P. rapae (2.71%); (2) PGF with B. ignitus depended on the distance between GM and non-GM cottons; (3) total PGF to Shiyuan321 (8.61%) was higher than to Hai7124 (4.10%). To confirm gene flow, we tested hybrids carrying transgenes for their resistance to glyphosate and H. armigera, and most hybrids showed strong resistance to the herbicide and insect. Our research confirmed that PGF depended on pollinator species, distance between plants and the receptor plant.

Pollen-Mediated Gene Flow in Maize: Implications for Isolation Requirements and Coexistence in Mexico, the Center of Origin of Maize

Mexico, the center of origin of maize (Zea mays L.), has taken actions to preserve the identity and diversity of maize landraces and wild relatives. Historically, spatial isolation has been used in seed production to maintain seed purity. Spatial isolation can also be a key component for a strategy to minimize pollen-mediated gene flow in Mexico between transgenic maize and sexually compatible plants of maize conventional hybrids, landraces, and wild relatives. The objective of this research was to generate field maize-to-maize outcrossing data to help guide coexistence discussions in Mexico. In this study, outcrossing rates were determined and modeled from eight locations in six northern states, which represent the most economically important areas for the cultivation of hybrid maize in Mexico. At each site, pollen source plots were planted with a yellow-kernel maize hybrid and surrounded by plots with a white-kernel conventional maize hybrid (pollen recipient) of the same maturity. Outcrossing rates were then quantified by assessing the number of yellow kernels harvested from white-kernel hybrid plots. The highest outcrossing values were observed near the pollen source (12.9% at 1 m distance). The outcrossing levels declined sharply to 4.6, 2.7, 1.4, 1.0, 0.9, 0.5, and 0.5% as the distance from the pollen source increased to 2, 4, 8, 12, 16, 20, and 25 m, respectively. At distances beyond 20 m outcrossing values at all locations were below 1%. These trends are consistent with studies conducted in other world regions. The results suggest that coexistence measures that have been implemented in other geographies, such as spatial isolation, would be successful in Mexico to minimize transgenic maize pollen flow to conventional maize hybrids, landraces and wild relatives.

Establishment and optimization of a regionally applicable maize gene-flow model

Because of the rapid development of transgenic maize, the potential effect of transgene flow on seed purity has become a major concern in public and scientific communities. Setting a proper isolation distance in field experiments and seed production is a possible solution to meet seed-quality standards and ensure adventitious contamination of products is below a specific threshold. By using a Gaussian plume model as basis and data recorded by meteorological stations as input, we have established a simple regionally applicable maize gene-flow model for prediction of the maximum threshold distances (MTD) at which gene-flow frequency is equal to or lower than a threshold value of 1 or 0.1 % (MTD1%, MTD0.1%). After optimization of the model variables, simulated outcrossing rate was a good fit to data obtained from field experiments (y = 1.156x, R (2) = 0.8913, n = 30, P < P 0.01). In the process of model calibration, it was found that only 15.82 % of the total amount of the pollen released by each plant participated in the dispersal process. The variable "a" for genetic pollen competitiveness between donor and recipient was introduced into our model, for the "Zinuo18" and "Su608" used, "a" was 17.47. Finally, the model was successfully used in the spring maize-growing region of Northeast China. The range of MTD1% and MTD0.1% in this region varied from 10 m to 49 m and from 17 m to 125 m, respectively.

Sensitivity of a real-time PCR method for the detection of transgenes in a mixture of transgenic and non-transgenic seeds of papaya (Carica papaya L.)

BACKGROUND

Genetically engineered (GE) ringspot virus-resistant papaya cultivars 'Rainbow' and 'SunUp' have been grown in Hawai'i for over 10 years. In Hawai'i, the introduction of GE papayas into regions where non-GE cultivars are grown and where feral non-GE papayas exist have been accompanied with concerns associated with transgene flow. Of particular concern is the possibility of transgenic seeds being found in non-GE papaya fruits via cross-pollination. Development of high-throughput methods to reliably detect the adventitious presence of such transgenic material would benefit both the scientific and regulatory communities.

RESULTS

We assessed the accuracy of using conventional qualitative polymerase chain reaction (PCR) as well as real-time PCR-based assays to quantify the presence of transgenic DNA from bulk samples of non-GE papaya seeds. In this study, an optimized method of extracting high quality DNA from dry seeds of papaya was standardized. A reliable, sensitive real-time PCR method for detecting and quantifying viral coat protein (cp) transgenes in bulk seed samples utilizing the endogenous papain gene is presented. Quantification range was from 0.01 to 100 ng/μl of GE-papaya DNA template with a detection limit as low as 0.01% (10 pg). To test this system, we simulated transgene flow using known quantities of GE and non-GE DNA and determined that 0.038% (38 pg) GE papaya DNA could be detected using real-time PCR. We also validated this system by extracting DNA from known ratios of GE seeds to non-GE seeds of papaya followed by real-time PCR detection and observed a reliable detection limit of 0.4%.

CONCLUSIONS

This method for the quick and sensitive detection of transgenes in bulked papaya seed lots using conventional as well as real-time PCR-based methods will benefit numerous stakeholders. In particular, this method could be utilized to screen selected fruits from maternal non-GE papaya trees in Hawai'i for the presence of transgenic seed at typical regulatory threshold levels. Incorporation of subtle differences in primers and probes for variations in cp worldwide should allow this method to be utilized elsewhere when and if deregulation of transgenic papaya occurs.

Detection of airborne genetically modified maize pollen by real-time PCR

The cultivation of genetically modified (GM) crops has raised numerous concerns in the European Union and other parts of the world about their environmental and economic impact. Especially outcrossing of genetically modified organisms (GMO) was from the beginning a critical issue as airborne pollen has been considered an important way of GMO dispersal. Here, we investigate the use of airborne pollen sampling combined with microscopic analysis and molecular PCR analysis as an approach to monitor GM maize cultivations in a specific area. Field trial experiments in the European Union and South America demonstrated the applicability of the approach under different climate conditions, in rural and semi-urban environment, even at very low levels of airborne pollen. The study documents in detail the sampling of GM pollen, sample DNA extraction and real-time PCR analysis. Our results suggest that this 'GM pollen monitoring by bioaerosol sampling and PCR screening' approach might represent an useful aid in the surveillance of GM-free areas, centres of origin and natural reserves.

Gene flow in genetically modified wheat

Understanding gene flow in genetically modified (GM) crops is critical to answering questions regarding risk-assessment and the coexistence of GM and non-GM crops. In two field experiments, we tested whether rates of cross-pollination differed between GM and non-GM lines of the predominantly self-pollinating wheat Triticum aestivum. In the first experiment, outcrossing was studied within the field by planting "phytometers" of one line into stands of another line. In the second experiment, outcrossing was studied over distances of 0.5-2.5 m from a central patch of pollen donors to adjacent patches of pollen recipients. Cross-pollination and outcrossing was detected when offspring of a pollen recipient without a particular transgene contained this transgene in heterozygous condition. The GM lines had been produced from the varieties Bobwhite or Frisal and contained Pm3b or chitinase/glucanase transgenes, respectively, in homozygous condition. These transgenes increase plant resistance against pathogenic fungi. Although the overall outcrossing rate in the first experiment was only 3.4%, Bobwhite GM lines containing the Pm3b transgene were six times more likely than non-GM control lines to produce outcrossed offspring. There was additional variation in outcrossing rate among the four GM-lines, presumably due to the different transgene insertion events. Among the pollen donors, the Frisal GM line expressing a chitinase transgene caused more outcrossing than the GM line expressing both a chitinase and a glucanase transgene. In the second experiment, outcrossing after cross-pollination declined from 0.7-0.03% over the test distances of 0.5-2.5 m. Our results suggest that pollen-mediated gene flow between GM and non-GM wheat might only be a concern if it occurs within fields, e.g. due to seed contamination. Methodologically our study demonstrates that outcrossing rates between transgenic and other lines within crops can be assessed using a phytometer approach and that gene-flow distances can be efficiently estimated with population-level PCR analyses.

Assessment of the influence of field size on maize gene flow using SSR analysis

One of the factors that may influence the rate of cross-fertilization is the relative size of the pollen donor and receptor fields. We designed a spatial distribution with four varieties of genetically-modified (GM) yellow maize to generate different sized fields while maintaining a constant distance to neighbouring fields of conventional white kernel maize. Samples of cross-fertilized, yellow kernels in white cobs were collected from all of the adjacent fields at different distances. A special series of samples was collected at distances of 0, 2, 5, 10, 20, 40, 80 and 120 m following a transect traced in the dominant down-wind direction in order to identify the origin of the pollen through SSR analysis. The size of the receptor fields should be taken into account, especially when they extend in the same direction than the GM pollen flow is coming. From collected data, we then validated a function that takes into account the gene flow found in the field border and that is very useful for estimating the % of GM that can be found in any point of the field. It also serves to predict the total GM content of the field due to cross fertilization. Using SSR analysis to identify the origin of pollen showed that while changes in the size of the donor field clearly influence the percentage of GMO detected, this effect is moderate. This study demonstrates that doubling the donor field size resulted in an approximate increase of GM content in the receptor field of 7%. This indicates that variations in the size of the donor field have a smaller influence on GM content than variations in the size of the receptor field.

A flexible quantitative methodology for the analysis of gene-flow between conventionally bred maize populations using microsatellite markers

Previous studies of gene-flow in agriculture have used a range of physical and biochemical markers, including transgenes. However, physical and biochemical markers are not available for all commercial varieties, and transgenes are difficult to use when trying to estimate gene flow in the field where the use of transgenes is often restricted. Here, we demonstrate the use of simple sequence repeat microsatellite markers (SSRs) to study gene flow in maize. Developing the first quantitative analysis of pooled SSR samples resulted in a high sampling efficiency which minimised the use of resources and greatly enhanced the possibility of hybrid detection. We were able to quantitatively distinguish hybrids in pools of ten samples from non-hybrid parental lines in all of the 24 pair-wise combinations of commercial varieties tested. The technique was used to determine gene flow in field studies, from which a simple model describing gene flow in maize was developed.

Pollen-mediated gene flow in flax (Linum usitatissimum L.): can genetically engineered and organic flax coexist?

Coexistence allows growers and consumers the choice of producing or purchasing conventional or organic crops with known standards for adventitious presence of genetically engineered (GE) seed. Flax (Linum usitatissimum L.) is multipurpose oilseed crop in which product diversity and utility could be enhanced for industrial, nutraceutical and pharmaceutical markets through genetic engineering. If GE flax were released commercially, pollen-mediated gene flow will determine in part whether GE flax could coexist without compromising other markets. As a part of pre-commercialization risk assessment, we quantified pollen-mediated gene flow between two cultivars of flax. Field experiments were conducted at four locations during 2006 and 2007 in western Canada using a concentric donor (20 × 20 m) receptor (120 × 120 m) design. Gene flow was detected through the xenia effect of dominant alleles of high α-linolenic acid (ALA; 18:3(cisΔ9,12,15)) to the low ALA trait. Seeds were harvested from the pollen recipient plots up to a distance of 50 m in eight directions from the pollen donor. High ALA seeds were identified using a thiobarbituric acid test and served as a marker for gene flow. Binomial distribution and power analysis were used to predict the minimum number of seeds statistically required to detect the frequency of gene flow at specific α (confidence interval) and power (1-β) values. As a result of the low frequency of gene flow, approximately 4 million seeds were screened to derive accurate quantification. Frequency of gene flow was highest near the source: averaging 0.0185 at 0.1 m but declined rapidly with distance, 0.0013 and 0.00003 at 3 and 35 m, respectively. Gene flow was reduced to 50% (O₅₀) and 90% (O₉₀) between 0.85 to 2.64 m, and 5.68 to 17.56 m, respectively. No gene flow was detected at any site or year > 35 m distance from the pollen source, suggesting that frequency of gene flow was ≤ 0.00003 (P = 0.95). Although it is not possible to eliminate all adventitious presence caused by pollen-mediated gene flow, through harvest blending and the use of buffer zones between GE and conventional flax fields, it could be minimized. Managing other sources of adventitious presence including seed mixing and volunteer populations may be more problematic.

Development of sampling approaches for the determination of the presence of genetically modified organisms at the field level

In order to comply with the European Union regulatory threshold for the adventitious presence of genetically modified organisms (GMOs) in food and feed, it is important to trace GMOs from the field. Appropriate sampling methods are needed to accurately predict the presence of GMOs at the field level. A 2-year field experiment with two maize varieties differing in kernel colour was conducted in Slovenia. Based on the results of data mining analyses and modelling, it was concluded that spatial relations between the donor and receptor field were the most important factors influencing the distribution of outcrossing rate (OCR) in the field. The approach for estimation fitting function parameters in the receptor (non-GM) field at two distances from the donor (GM) field (10 and 25 m) for estimation of the OCR (GMO content) in the whole receptor field was developed. Different sampling schemes were tested; a systematic random scheme in rows was proposed to be applied for sampling at the two distances for the estimation of fitting function parameters for determination of OCR. The sampling approach had already been validated with some other OCR data and was practically applied in the 2009 harvest in Poland. The developed approach can be used for determination of the GMO presence at the field level and for making appropriate labelling decisions. The importance of this approach lies in its possibility to also address other threshold levels beside the currently prescribed labelling threshold of 0.9% for food and feed.

Fuzzy-logic based strategy for validation of multiplex methods: example with qualitative GMO assays

This paper illustrates the advantages that a fuzzy-based aggregation method could bring into the validation of a multiplex method for GMO detection (DualChip GMO kit, Eppendorf). Guidelines for validation of chemical, bio-chemical, pharmaceutical and genetic methods have been developed and ad hoc validation statistics are available and routinely used, for in-house and inter-laboratory testing, and decision-making. Fuzzy logic allows summarising the information obtained by independent validation statistics into one synthetic indicator of overall method performance. The microarray technology, introduced for simultaneous identification of multiple GMOs, poses specific validation issues (patterns of performance for a variety of GMOs at different concentrations). A fuzzy-based indicator for overall evaluation is illustrated in this paper, and applied to validation data for different genetically modified elements. Remarks were drawn on the analytical results. The fuzzy-logic based rules were shown to be applicable to improve interpretation of results and facilitate overall evaluation of the multiplex method.

Sampling and modeling for the quantification of adventitious genetically modified presence in maize

The coexistence of genetically modified (GM) and non-GM crops is an important economic and political issue in the European Union. We examined the GM content in non-GM maize crops in Spain in 2005. Both the standing crop and the harvest were tested, and the %GM DNA was quantified by real-time polymerase chain reaction. We compared the level of GM as a function of distance from known GM source fields in a 1.2 km2 landscape. The distribution of GM was compared to predictions from previous studies, and good agreement was found. Control and monitoring of adventitious GM presence in non-GM crops can only be achieved by fit-for-purpose sampling and testing schemes. We used a GM dispersal function to simulate non-GM crops in the studied zone and tested the accuracy of five different sampling schemes. Random sampling was found to be the most accurate and least susceptible to bias by GM spatial structure or gradients. Simulations showed that to achieve greater than 95% confidence in a GM labeling decision of a harvest (when treated as a single marketed lot), 34 samples would be needed when the harvest was outside 50% of the GM threshold value. The number of samples required increased rapidly as the harvest approached the GM threshold, implying that accurate labeling when the harvest is within +/-17% of the threshold may not be possible with high confidence.

Regulating coexistence of GM and non-GM crops without jeopardizing economic incentives

The ongoing debate about the coexistence of genetically modified (GM) and non-GM crops in the European Union (EU) mainly focuses on preventive measures needed to keep the adventitious presence of GM material in non-GM products below established tolerance thresholds, as well as on issues covering questions of liability and the duty to redress the incurred economic harm once adventitious mixing in non-GM products has occurred. By contrast, the interplay between the economic incentives and costs of coexistence has attracted little attention. The current overemphasis on the technical aspects and cost of coexistence over its economic incentives might lead EU policy-makers to adopt too stringent and rigid regulations on coexistence. Therefore, we argue for flexible coexistence regulations that explicitly take into account the economic incentives for coexistence. Our arguments provide a timely and important framework for EU policy-makers, who are currently struggling to implement coherent coexistence regulations in all member states.

Outcrossed cottonseed and adventitious Bt plants in Arizona refuges

Outcrossing of non-Bt cotton (Gossypium hirsutum (L.)) in refuges by transgenic Bt cultivars could reduce the efficacy of refuges for delaying resistance in seed-feeding pests. Based on reports that outcrossing decreased as distance from Bt cotton increased in small-scale studies, we hypothesized that increasing refuge width or distance from Bt fields would reduce outcrossing. In a large-scale study in Arizona, we quantified Bt seed in refuges of experimental and commercial fields, comparing outcrossing between in-field (narrow) and external (wide) refuges and among rows of refuges at various distances from Bt fields. Some refuges, including those in tightly controlled experimental plots, contained up to 8% adventitious Bt plants. Some, but not all, Bt plants likely resulted from Bt seed in the non-Bt seed bags. We did not detect a difference in outcrossing between in-field and external refuges. However, statistical power was low because outcrossing was low (< 0.4% of seeds) in both treatments. Higher outcrossing levels (< or = 4.6% of seeds) were observed in the studies measuring outcrossing at various distances from Bt fields, yet outcrossing did not decrease as the distance from Bt fields increased. We hypothesize that Bt plants in refuges cross-pollinated surrounding non-Bt plants, overshadowing the expected association between distance from Bt fields and outcrossing.

Impact of genetic structures on haploid genome-based quantification of genetically modified DNA: theoretical considerations, experimental data in MON 810 maize kernels (Zea mays L.) and some practical applications

Real-time Polymerase Chain Reaction (PCR) based assays are widely used to estimate the content of genetically modified (GM) materials in food, feed and seed. It has been known that the genetic structures of the analyte can significantly influence the GM content expressed by the haploid genome (HG) % estimated using real-time PCR assays; this kind of influence is also understood as the impact of biological factors. The influence was first simulated at theoretical level using maize as a model. We then experimentally assessed the impact of biological factors on quantitative results, analysing by quantitative real-time PCR six maize MON 810 hybrid kernels with different genetic structures: (1) hemizygous from transgenic male parent, (2) hemizygous from transgenic female parent and (3) homozygous at the transgenic locus. The results obtained in the present study showed clear influences of biological factors on GM DNA quantification: 1% of GM materials by weight (wt) for the three genetic structures contained 0.39, 0.55 and 1.0% of GM DNA by HG respectively, from quantitative real-time PCR analyses. The relationships between GM wt% and GM HG% can be empirically established as: (1) in the case of the presence of a single GM trait: GM HG% = GM wt% x (0.5 +/- 0.167Y), where Y is the endosperm DNA content (%) in the total DNA of a maize kernel, (2) in the case of the presence of multiple GM traits: GM HG% = N x GM wt% x (0.5 +/- 0.167Y), where N is the number of GM traits (stacked or not) present in an unknown sample. This finding can be used by stakeholders related to GMO for empirical prediction from one unit of expression to another in the monitoring of seed and grain production chains. Practical equations have also been suggested for haploid copy number calculations, using hemizygous GM materials for calibration curves.

Definition and feasibility of isolation distances for transgenic maize cultivation

A major concern related to the adoption of genetically modified (GM) crops in agricultural systems is the possibility of unwanted GM inputs into non-GM crop production systems. Given the increasing commercial cultivation of GM crops in the European Union (EU), there is an urgent need to define measures to prevent mixing of GM with non-GM products during crop production. Cross-fertilization is one of the various mechanisms that could lead to GM-inputs into non-GM crop systems. Isolation distances between GM and non-GM fields are widely accepted to be an effective measure to reduce these inputs. However, the question of adequate isolation distances between GM and non-GM maize is still subject of controversy both amongst scientists and regulators. As several European countries have proposed largely differing isolation distances for maize ranging from 25 to 800 m, there is a need for scientific criteria when using cross-fertilization data of maize to define isolation distances between GM and non-GM maize. We have reviewed existing cross-fertilization studies in maize, established relevant criteria for the evaluation of these studies and applied these criteria to define science-based isolation distances. To keep GM-inputs in the final product well below the 0.9% threshold defined by the EU, isolation distances of 20 m for silage and 50 m for grain maize, respectively, are proposed. An evaluation using statistical data on maize acreage and an aerial photographs assessment of a typical agricultural landscape by means of Geographic Information Systems (GIS) showed that spatial resources would allow applying the defined isolation distances for the cultivation of GM maize in the majority of the cases under actual Swiss agricultural conditions. The here developed approach, using defined criteria to consider the agricultural context of maize cultivation, may be of assistance for the analysis of cross-fertilization data in other countries.

A study of crop-to-crop gene flow using farm scale sites of fodder maize (Zea mays L.) in the UK

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 x 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.

A new PCR-CGE (size and color) method for simultaneous detection of genetically modified maize events

We present a novel multiplex PCR assay for simultaneous detection of multiple transgenic events in maize. Initially, five PCR primers pairs specific to events Bt11, GA21, MON810, and NK603, and Zea mays L. (alcohol dehydrogenase) were included. The event specificity was based on amplification of transgene/plant genome flanking regions, i.e., the same targets as for validated real-time PCR assays. These short and similarly sized amplicons were selected to achieve high and similar amplification efficiency for all targets; however, its unambiguous identification was a technical challenge. We achieved a clear distinction by a novel CGE approach that combined the identification by size and color (CGE-SC). In one single step, all five targets were amplified and specifically labeled with three different fluorescent dyes. The assay was specific and displayed an LOD of 0.1% of each genetically modified organism (GMO). Therefore, it was adequate to fulfill legal thresholds established, e.g., in the European Union. Our CGE-SC based strategy in combination with an adequate labeling design has the potential to simultaneously detect higher numbers of targets. As an example, we present the detection of up to eight targets in a single run. Multiplex PCR-CGE-SC only requires a conventional sequencer device and enables automation and high throughput. In addition, it proved to be transferable to a different laboratory. The number of authorized GMO events is rapidly growing; and the acreage of genetically modified (GM) varieties cultivated and commercialized worldwide is rapidly increasing. In this context, our multiplex PCR-CGE-SC can be suitable for screening GM contents in food.