Gene flow from herbicide-tolerant GM rice and the heterosis of GM rice-weed F2 progeny

Gene flow from genetically modified (GM) crops to non-GM cultivars or weedy relatives may lead to the development of more aggressive weeds. We quantified the amount of gene flow from herbicide-tolerant GM rice (Protox GM, derived from the cultivar Dongjin) to three cultivars (Dongjin, Aranghyangchal and Hwaseong) and a weedy rice line. Gene flow frequency generally decreased with increasing distance from the pollen donor. At the shortest distance (0.5 m), we observed a maximum frequency (0.039%) of gene flow. We found that the cultivar Dongjin received the greatest amount of gene flow, with the second being weedy rice. Heterosis of F2 inbred progeny was also examined between Protox GM and weedy rice. We compared growth and reproduction between F2 progeny (homozygous or hemizygous for the Protox gene) and parental rice lines (GM and weedy rice). Here, transgene-homozygous F2 progeny was significantly taller and produced more seeds than the transgene-hemizygous F2 progeny and parental lines. Although the gene flow frequency was generally low, our results suggest that F2 progeny between GM and weedy relatives may exhibit heterosis.     

Investigation of rice transgene flow in compass sectors by using male sterile line as a pollen detector

Rice is the most important staple food in the world. The rapid development of transgenic rice and its future commercialization have raised concerns regarding transgene flow and its potential environmental risk. It is known that rice is a self-pollinated crop; the outcrossing rate between common cultivars is generally less than 1%. In order to improve the detection sensitivity of rice transgene flow, a male sterile (ms) line BoA with a high outcrossing rate was used as a pollen detector in this study. A concentric circle design was adopted, in which the transgenic rice B2 containing bar gene as a pollen donor was planted in the center circle and the recipient BoA was planted in eight compass sectors. The frequency of transgene flow in compass sectors was analyzed by continuous sampling to generate cumulative data. The results of two years with sound reproducibility demonstrated that the rice gene flow was closely associated with the wind direction. According to the mean frequency of transgene flow, the eight sectors can be divided into two groups: a higher frequency group downstream of the prevailing wind (DPW) with a mean frequency ranging from 6.47 to 26.24%, and a lower frequency group lateral to or upstream of the prevailing wind (UPW) with a mean frequency of 0.39 to 3.03%. On the basis of the cumulative data, 90–96% of the cumulative gene flow events occurred in the four DPW sectors, while it was 4–10% in the four UPW sectors. By using these systematic data, simulation models and isograms of transgene flow in the eight compass sectors were calculated and drawn, respectively. Q. H. Yuan, L. Shi and S. R. Jia contributed equally to the work.     

Establishment of a rice transgene flow model for predicting maximum distances of gene flow in southern China

We aimed to establish a rice gene flow model based on (i) the Gaussian plume model, (ii) data from a three-location x 3-yr field experiment on transgene flow to common rice cultivars (Oryza sativa), male sterile (ms) lines (O. sativa) and common wild rice (Oryza rufipogon), and (iii) 32-yr historical meteorological data collected from 38 meteorological stations in southern China during the rice flowering period. The concept of the gene flow coefficient (GFC) is proposed; that is, the ratio of the transgene flow frequency (G%) obtained from field experiments to the aggregated pollen dispersal frequency (P%) calculated based on the pollen dispersal model. The maximum distances of gene flow (MDGF) to traditional rice cultivars, ms lines, and common wild rice at a threshold value of either 1.0 or 0.1% were determined. The MDGF and its spatial distribution in southern China show that the gene flow pattern is significantly affected by the monsoon climate, the topography, and the outcrossing ability of recipients. We believe that the information provided in this study will be useful for the risk assessment of transgenic rice in other rice-growing regions.     

The EPSPS gene flow from glyphosate-resistant Brassica napus to untransgene B. napus and wild relative species Orychophragmus violaceus

Gene flow from transgenic plants to compatible wild relatives is one of the major impediments to the development of the culture of genetically engineered crop plants. In this work, the flow of EPSPS (conferring resistance to glyphosate) gene of transgene Brassica napus toward the untransgene B. napus and wild relative species Orychophragmus violaceus in an open field (1 ha) was studied. The data related to only the 2004 and 2005 autumn season on one location of southwest of China. Pollen dispersal and fertilization of the target plants were favored and a detailed analysis of the hybrid offspring was performed. In field, the data studied show that the gene flow frequency was 0.16% between GM and non-GM B. napus at a distance of 1 m from the transgenic donor area. The crosspollination frequency was 0.05% between GM and non-GM B. napus at a distance of 5 m from the transgenic donor area. At a distance of 10 m, no crosspollination was observed. According to the results of this study, B. napus transgene flow was low. However, the wild relative species O. violaceus could not be fertilized by the transgenic pollen of B. napus, no matter what the distance was.     

家蝇介导的水稻基因逃逸风险评估(英文)

【目的】对转基因作物进行生态风险评估是大面积种植前的一个必要步骤,水稻Oryza sativa访花昆虫有上百种,包括家蝇Musca domestica。本研究旨在明确访花昆虫家蝇介导转基因水稻外源基因逃逸的风险。【方法】2010年,我们使用转基因水稻B1, B6和G8-7作为父本(花粉供体),用同源非转基因水稻Jiazao 935和Wuyunjing 7作为母本（花粉受体）,并用家蝇作为授粉昆虫,在浙江大学华家池和长兴试验基地开展了田间种植试验,对收割的后代水稻种子进行室内种植培养,对种苗用潮霉素B和草甘膦处理进行转基因杂交种检测,对存活植株进行潮霉素和草甘膦抗性基因PCR检测,测试家蝇介导的转基因水稻外源基因逃逸频率。【结果】对浙江两个测试基地3个转基因水稻品种共计超过216 500粒后代水稻种子进行的检测及结果表明,在毗邻区域杂交种少,家蝇授粉区和无家蝇授粉区转基因水稻外源基因向非转基因水稻逃逸频率均较低(0~0.64%)。【结论】家蝇介导的转基因水稻外源基因逃逸频率较低,家蝇没有增加转基因水稻外源基因逃逸的风险。     

Rice transgene flow: its patterns,model and risk management

Progress has been made in a 12 year's systemic study on the rice transgene flow including (i) with experiments conducted at multiple locations and years using up to 21 pollen recipients, we have elucidated the patterns of transgene flow to different types of rice. The frequency to male sterile lines is 10¹ and 10³ higher than that to O. rufipogon and rice cultivars. Wind speed and direction are the key meteorological factors affecting rice transgene flow. (ii) A regional applicable rice gene flow model is established and used to predict the maximum threshold distances (MTDs) of gene flow during 30 years in 993 major rice producing counties of southern China. The MTD_0.1% for rice cultivars is basically ≤5 m in the whole region, despite climate differs significantly at diverse locations and years. This figure is particularly valuable for the commercialization and regulation of transgenic rice. (iii) The long‐term fate of transgene integrated into common wild rice was investigated. Results demonstrated that the F₁ hybrids of transgenic rice/O. rufipogon gradually disappeared within 3–5 years, and the Bt or bar gene was not detectable in the mixed population, suggesting the O. rufipogon may possess a strong mechanism of exclusiveness for self‐protection. (iv) The flowering time isolation and a 2‐m‐high cloth‐screen protection were proved to be effective in reducing transgene flow. We have proposed to use a principle of classification and threshold management for different types of rice.     

Detection of gene flow from GM to non-GM watermelon in a field trial

Gene flow from genetically modified (GM) crops to conventional non-GM crops is a serious concern for protection of conventional and organic farming. Gene flow from GM watermelon developed for rootstock use, containing cucumber green mottle mosaic virus (CGMMV)-coat protein (CP) gene, to a non-GM isogenic control variety “Clhalteok” and grafted watermelon “Keumcheon” was investigated in a small scale field trial as a pilot study. Hybrids between GM and non-GM watermelons were screened from 1304 “Chalteok” seeds and 856 “Keumcheon” seeds using the duplex PCR method targeting theCGMMV- CP gene as a marker. Hybrids were found in all pollen recipient plots. The gene flow frequencies were greater for “Chaiteok” than for “KeumcheonD; with 75% outcrossing in the “Chaiteok” plot at the closest distance (0.8 m) to the GM plot. A much larger scale field trial is necessary to identify the isolation distance between GM and non-GM watermelon, as the behaviors of insect pollinators needs to be clarified in Korea.     

Pollen flow of cultivated rice measured under experimental conditions

The pollen flow pattern of a cultivated rice variety, Minghui-63, was studied at horizontal and vertical levels under experimental conditions. Data obtained from pollen traps for six designed populations (as pollen sources) at different intervals showed that the dispersal of rice pollen decreased with the increase of distance from pollen sources and that the rice pollen flow was significantly influenced by weather conditions, particularly by wind direction and speed. For a mean wind speed of 2.52 m/s in a downwind direction, the observed distance of rice pollen dispersal was 38.4 m, indicating that rice pollen grains normally disperse at a relatively small range. However, the maximum distance of rice pollen flow could be up to 110 m, using regression analysis of pollen flow and wind speed, when the wind speed reached 10 m/s in this study. The frequency of pollen flow was positively correlated with pollen source size within a given range, suggesting that pollen flow will occur effectively at a considerable rate in rice fields with sufficiently large pollen sources. In addition, many more pollen grains were detected at the height of 1.0–1.5 m than at 2.0 m, indicating that rice pollen mainly disperses at relatively low heights. Results from this study are useful both for minimizing transgene escape from transgenic rice and in situ conservation of wild relatives of rice, as well as for hybrid seed production, where an effective isolation buffer zone needs to be established.     

Assessment of Gene Flow from Genetically Modified Anthracnose-Resistant Chili Pepper (Capsicum annuum L.) to a Conventional Crop

We conducted a 2-year field assessment of the gene flow from genetically modified (GM) chili pepper (Capsicum annuum L.), containing the PepEST (pepper esterase) gene, to a non-GM control line “WT512” and two commercial hybrid cultivars, “Manidda” and “Cheongpung Myeongwol (CM).” After seeds were collected from the pollen-recipient non-GM plants, hybrids between them and the GM peppers were screened by a hygromycin assay. PCR with the targeting hpt gene was performed to confirm the presence of transgenes in hygromycin-resistant seedlings. Out of 7,071 “WT512” seeds and 6,854 “Manidda” seeds collected in 2006, eight and 12 hybrids, respectively, were detected. In 2007, 33 hybrids from 3,456 “WT512” seeds and 50 hybrids from 3,457 “CM” seeds were found. The highest frequency of gene flow, 6.19%, was observed in that 2007 trial. These results suggest that a limited isolation distance would be sufficient to prevent gene flow from GM to conventionally bred chili peppers.     

Utilization of the bar gene to develop an efficient method for detection of the pollen-mediated gene flow in Chinese cabbage (Brassica rapa spp. pekinensis)

To develop an efficient screening method for detection of the transgene in Chinese cabbage (Brassica rapa spp. pekinensis) utilizing Basta spray, optimal conditions for Basta application were examined in this study. Two transgenic Chinese cabbage lines were obtained through Agrobacterium-mediated transformation and used as transgenic positive controls in the Basta screening experiment. Differential concentrations of glufosinate-ammonium were sprayed into three different growth stages of 12 commercial Chinese cabbage cultivars. The results showed that no plants could survive higher than 0.05% glufosinate-ammonium, and plants at the 2–3 leaf stage were most vulnerable to glufosinate-ammonium. On the other hand, no damage was observed in the transgenic control plants. Reliability of the Basta spray method was proven by showing perfect co-segregation of the tolerance to glufosinate-ammonium and the presence of the bar gene in T₁ segregating populations of the transgenic lines, as revealed by both PCR and Southern blot analyses. Using the developed Basta screening method, we tried to investigate the transgene flow through pollen dispersal, but failed to detect any transgene-containing non-transgenic Chinese cabbages whose parents had been planted adjacent to transgenic Chinese cabbages in field conditions. However, the transgene was successfully detected using Basta spray from the non-transgenic plants bearing the transgene introduced by hand-pollination. Since the Basta spray method developed in this study is easy to apply and economical, it will be a valuable tool for understanding the mechanism of gene flow through pollen transfer and for establishing a biosafety test protocol for genetically modified (GM) Chinese cabbage cultivars.     

Gene flow from genetically modified rice to its wild relatives: Assessing potential ecological consequences

Pollen-mediated gene flow is the major pathway for transgene escape from GM rice to its wild relatives. Transgene escape to wild Oryza species having AA-genome will occur if GM rice is released to environments with these wild Oryza species. Transgenes may persist to and spread in wild populations after gene flow, resulting unwanted ecological consequences. For assessing the potential consequences caused by transgene escape, it is important to understand the actual gene flow frequencies from GM rice to wild relatives, transgene expression and inheritance in the wild relatives, as well as fitness changes that brought to wild relatives by the transgenes. This article reviews studies on transgene escape from rice to its wild relatives via gene flow and its ecological consequences. A framework for assessing potential ecological consequences caused by transgene escape from GM rice to its wild relatives is discussed based on studies of gene flow and fitness changes.     

Apomixis and ploidy barrier suppress pollen-mediated gene flow in field grown transgenic turf and forage grass (Paspalum notatum Flüggé)

Bahiagrass (Paspalum notatum Flüggé) is the predominant forage grass in the southeastern US. The commercially important bahiagrass cultivar ‘Argentine’ is preferred for genetic transformation over sexual diploid cytotypes, since it produces uniform seed progeny through apomixis. Pseudogamous apomictic seed production in Argentine bahiagrass may contribute to transgene confinement. It is characterized by embryo development which is independent of fertilization of the egg cell, but requires fertilization with compatible pollen to produce the endosperm. Pollen-mediated gene transfer from transgenic, glufosinate-resistant apomictic bahiagrass as pollen donor at close proximity (0.5–3.5 m) with non-transgenic sexual or apomictic bahiagrass cultivars as pollen receptors was evaluated under field conditions. Hybridization frequency was evaluated by glufosinate herbicide resistance in >23,300 seedlings derived from open-pollinated (OP) pollen receptor plants. Average gene transfer between transgenic apomictic, tetraploid and sexual diploid bahiagrass was 0.03%. Herbicide-resistant hybrids confirmed by immuno-chromatographic detection of the PAT protein displayed a single copy bar gene identical to the pollen parent. Hybrids resulting from diploid pollen receptors were confirmed as triploids or aneu-triploids with significantly reduced vigor and seed set as compared to the parents. Transmission of transgenes to sexual bahiagrass is severely restricted by the ploidy difference between tetraploid apomicts and diploid sexual bahiagrass. Average gene transfer between transgenic apomictic tetraploid and non-transgenic, apomictic tetraploid bahiagrass was 0.17%, confirming a very low frequency of amphimixis in apomictic bahiagrass cultivars. While not providing complete transgene containment, gene transfer between transgenic apomictic and non-transgenic bahiagrass occurs at a much lower frequency than reported for other cross-pollinating or facultative apomictic grasses.     

A large-scale field study of transgene flow from cultivated rice (Oryza sativa) to common wild rice (O. rufipogon) and barnyard grass (Echinochloa crusgalli)

The introgression of transgenes into wild relatives or weeds through pollen-mediated gene flow is a major concern in environmental risk assessment of transgenic crops. A large-scale (1.3–1.8 ha) rice gene flow study was conducted using transgenic rice containing the bar gene as a pollen donor and Oryza rufipogon as a recipient. There was a high frequency of transgene flow (11%−18%) at 0–1 m, with a steep decline with increasing distance to a detection limit of 0.01% by 250 m. To our knowledge, this is the highest frequency and longest distance of gene flow from transgenic rice to O. rufipogon reported so far. On the basis of these data, an adequate isolation distance from both conventional and transgenic rice should be taken for in situ conservation of common wild rice. Meanwhile, there is no evidence of transgene introgression into barnyard grass, even when it has coexisted with transgenic rice containing the bar gene for five successive years. Thus, the environmental risk of gene flow to this weedy species is of little concern.     

Assessment of gene flow from a herbicide-resistant indica rice (Oryza sativa L.) to the Costa Rican weedy rice (Oryza sativa) in Tropical America: factors affecting hybridization rates and characterization of F1 hybrids

Herbicide-resistant rice cultivars allow selective weed control. A glufosinate indica rice has been developed locally. However, there is concern about weedy rice becoming herbicide resistant through gene flow. Therefore, assessment of gene flow from indica rice cultivars to weedy rice is crucial in Tropical America. A field trial mimicking crop–weed growing patterns was established to assess the rate of hybridization between a Costa Rican glufosinate-resistant rice line (PPT-R) and 58 weedy rice accessions belonging to six weedy rice morphotypes. The effects of overlapping anthesis, morphotype, weedy accession/PPT-R percentage, and the particular weedy accession on hybridization rates were evaluated. Weedy rice accessions with short overlapping anthesis (4–9 days) had lower average hybridization rates (0.1%) than long anthesis overlapping (10–14 days) accessions (0.3%). Hybridization also varied according to weedy rice morphotype and accession. Sativa-like morphotypes (WM-020, WM-120) hybridized more readily than intermediate (WM-023, WM-073, WM-121) and rufipogon-like (WM-329) morphotypes. No hybrids were identified in 11 of the 58 accessions analyzed, 21 accessions had hybridization rates from 0.01% to 0.09%, 21 had rates from 0.1% to 0.9%, and 5 had frequencies from 1% to 2.3%. Another field trial was established to compare the weedy rice-PPT-R F₁ hybrids with their parental lines under noncompetitive conditions. F₁ hybrids had a greater phenotypic variation. They had positive heterosis for vegetative trait and reproductive potential (number of spikelets and panicle length) traits, but negative heterosis for seed set. This study demonstrated the complexity of factors affecting hybridization rates in Tropical America and suggested that the phenotype of F₁ hybrids facilitate their identification in the rice fields.     

Risk assessment of transgenic apomictic tetraploid bahiagrass,cytogenetics, breeding behavior and performance of intra-specific hybrids

Pollen-mediated gene transfer from stress tolerant or herbicide-resistant transgenic plants may cause environmental or agronomic problems. Apomictic seed production found in some bahiagrass cultivars may serve as a natural transgene containment system. Under greenhouse conditions, the average gene transfer frequency from an herbicide-resistant apomictic tetraploid to a population of sexual diploid bahiagrass genotypes or apomictic tetraploid bahiagrass was 0.16% when the transgenic pollen donor was placed at 0.5–1.5 m distance from the non-transgenic pollen receptors. The herbicide-resistant hybrids were characterized for transgene integration, expression and ploidy, by Southern blot analysis, immuno-chromatography and flow cytometry, respectively. Hybrids resulting from open pollination of non-transgenic diploid female plants with transgenic tetraploid male plants were triploids or near-triploids, with 2n = 26–34. These hybrids displayed a wide range of phenotypic variability, including some non-persistent or non-flowering dwarf-type hybrids with good vigor, or hybrids with vegetative growth similar to non-transgenic plants, but with significantly reduced seed set. Non-flowering aneu-triploids with good vigor/field performance will provide the highest level of transgene containment. Embryo sac analysis of pollinated spikelets confirmed a high proportion of aborted ovules. An apospory-linked RFLP marker was detected in 13 of the 15 near-triploid hybrids. All flowering aneuploid hybrids displayed significantly reduced seed set, and none of the sexual near-triploid hybrids produced any seeds. All tetraploid gene transfer events carried the apospory-linked RFLP marker, suggesting that despite the presence of the aposporus locus, a low degree of sexuality co-exists in apomictic tetraploid cultivars. Thus, tetraploid apomictic bahiagrass does not provide complete transgene containment, although intra-specific gene transfer is drastically reduced compared to sexually reproducing perennial grasses.     

Induction of male sterility in transgenic chrysanthemums (Chrysanthemum morifolium Ramat.) by expression of a mutated ethylene receptor gene, Cm-ETR1/H69A, and the stability of this sterility at varying growth temperatures

Chrysanthemum (Chrysanthemum morifolium Ramat.) is one of the most popular ornamental flowers in the world, and many agronomic traits have recently been introduced to chrysanthemum cultivars by gene transformation. Concerns have been raised, however, regarding transgene flow from transgenic plants to wild plants. In early studies, ethylene receptor genes have been used for genetic modification in plants, such as flower longevity and fruit ripening. Recently, overexpression of ethylene receptor genes from melon (CmETR1/H69A) caused delayed tapetum degradation of the anther sac and a reduction in pollen grains. We therefore introduced the ethylene receptor gene into chrysanthemums to induce male sterility and prevent transgene flow via pollen. The chrysanthemum cultivar Yamate shiro was transformed using a disarmed strain of Agrobacterium tumefaciens, EHA105, carrying the binary vector pBIK102H69A, which contains the CmETR1/H69A gene. A total of 335 shoots were regenerated from 1,282 leaf discs on regeneration medium (26.1%). The presence of the Cm-ETR1/H69A gene was confirmed in all of the regenerated plantlets by Southern blot analysis. These genetically modified (GM) plants and their non-GM counterparts were grown in a closed greenhouse and flowered at temperatures between 10 and 35°C. In 15 of the 335 GM chrysanthemum lines, the number of mature pollen grains was significantly reduced, particularly in three of the lines (Nos. 91, 191 and 324). In these three lines, pollen grains were not observed at temperatures between 20 and 35°C but were observed at 10 and 15°C, and mature pollen grains were formed only at 15°C. In northern blot analyses, expression of the CmETR1/H69A gene was suppressed at low temperatures. This phenomenon was observed as a result of both the suppression of CmETR1/H69A expression at low temperatures and the optimal growth temperature of chrysanthemums (15–20°C). Furthermore, the female fertility of these three GM lines was significantly lower than that of the non-GM plants. Thus, the mutated ethylene receptor is able to reduce both male and female fertility significantly in transgenic chrysanthemums, although the stability of male and/or female sterility at varying growth temperatures is a matter of concern for its practical use.     

Pollen flow in Eucalyptus grandis determined by paternity analysis using microsatellite markers

Gene flow by pollen dispersal from forestry plantations containing introduced species, provenances or selected elite breeding material may impact on local native forest by changing the genetic diversity, introducing new genes or gene combinations, or causing the extinction of rare genotypes in adjacent native forest areas. Patterns of pollen flow can be used to assess the risk of genetic pollution of native forest areas from nearby plantations. Pollen flow in an artificial population of Eucalyptus grandis was estimated using molecular markers and paternity analysis. Microsatellite genotyping was used to identify pollen parents of progeny arrays from six mother trees. Of 329 progeny analysed, 178 (54%) were assigned to pollen parents within the population. Pollen parents located within the population were between 0–192 m from the respective mother trees, with an average pollination distance of 57.96 m. Pollination of mother trees was outcrossed, not by nearest neighbours, and displayed a preference for inter-provenance matings within the population. Progeny that could not be assigned pollen parents within the population (46%) were assumed to have resulted from pollen immigration from external sources. These pollen flow parameters provide useful information about the dynamics of pollen movement within E. grandis populations and may be used in risk assessment of gene flow from plantations to adjacent areas of native forest.     

An assessment of gene transfer by pollen from field-grown transgenic potatoes to non-transgenic potatoes and related species

Information on the extent of transgene dispersal by pollen to adjacent potato plots and to related weed species is an important requisite for risk assessment; a procedure followed before novel transgenic plants are evaluated under field conditions. The purpose of the investigation was to determine the frequency of cross-pollination between potato (Solanum tuberosum) plants at different distances, using a kanamycin resistnace transgene (nptII) as a selectable marker. All potato plants were from the variety Désirée. Non-transgenic potato plants, used as potential recipients of transgene-containing pollen, were planted in 12 sub-plots, at distances of 0–20 m from the nearest transgenic potato plants. Seeds harvested from the non-transgenic plants were screened for resistance to kanamycin, and molecular methods were used to confirm that resistant progeny contained thenptII gene. Where transgenic and non-transgenic potato plants were in alternate rows (leaves touching), 24% of seedlings from the non-transgenic parent plants were kanamycin-resistant. Comparable seedlings from plants at up to 3 m distance had a resistance frequency of 2%, at 10 m the frequency was 0.017% and at 20 m no resistant progeny were observed. Plants of the weed speciesS. dulcamara andS. nigrum were also planted close to the transgenic potatoes to test for evidence of hybridization, and no kanamycin-resistant seedlings were observed among progeny fromS. dulcamara andS. nigrum. This investigation provided evidence that the extent of gene dispersal from transgenic potatoes to non-transgenic potatoes falls markedly with increasing distance, and is negligible at 10 m. There was, also, no evidence of transgene movement from potato toS. dulcamara andS. nigrum under field conditions. These data will be valuable in defining genetic isolation procedures for the early field evaluation and the use of novel transgenic potato genotypes.     

Low frequency of transgene flow from Bt/CpTI rice to its non-transgenic counterparts planted at close spacing

Crop-to-crop transgene flow will affect seed purity of non-GM rice varieties, leading to unwanted consequences. To assess the maximum probability of transgene outflow in rice (Oryza sativa), gene flow experiments were conducted with three cultivation patterns with different mixed-planting proportions of adjacent GM and non-GM rice at two sites in Fujian and Hainan Provinces of China. Three GM rice lines containing two insect-resistance genes (Bt/CpTI) and their non-GM counterparts were used in the experiments to allow natural hybridization to occur. A hygromycin resistance gene was used as a selective marker for identifying hybrids. Based on the examination of > 645 700 geminated seeds, the result showed low frequencies (0.05-0.79%) of transgene flow from GM to non-GM rice at close spacing, although with significant variation among mixed-planting proportions. It is concluded that rice transgene flow will occur at a very low frequency (< 1.0%), even if the GM rice is planted at close spacing with non-GM rice, and high densities of GM rice cultivated in the neighborhood of non-GM rice will increase the probability of outcrossing with the non-GM rice.     

Investigating Pollen and Gene Flow of WYMV-Resistant Transgenic Wheat N12-1 Using a Dwarf Male-Sterile Line as the Pollen Receptor

Pollen-mediated gene flow (PMGF) is the main mode of transgene flow in flowering plants. The study of pollen and gene flow of transgenic wheat can help to establish the corresponding strategy for preventing transgene escape and contamination between compatible genotypes in wheat. To investigate the pollen dispersal and gene flow frequency in various directions and distances around the pollen source and detect the association between frequency of transgene flow and pollen density from transgenic wheat, a concentric circle design was adopted to conduct a field experiment using transgenic wheat with resistance to wheat yellow mosaic virus (WYMV) as the pollen donor and dwarf male-sterile wheat as the pollen receptor. The results showed that the pollen and gene flow of transgenic wheat varied significantly among the different compass sectors. A higher pollen density and gene flow frequency was observed in the downwind SW and W sectors, with average frequencies of transgene flow of 26.37 and 23.69% respectively. The pollen and gene flow of transgenic wheat declined dramatically with increasing distance from its source. Most of the pollen grains concentrated within 5 m and only a few pollen grains were detected beyond 30 m. The percentage of transgene flow was the highest where adjacent to the pollen source, with an average of 48.24% for all eight compass directions at 0 m distance. Transgene flow was reduced to 50% and 95% between 1.61 to 3.15 m, and 10.71 to 20.93 m, respectively. Our results suggest that climate conditions, especially wind direction, may significantly affect pollen dispersal and gene flow of wheat. The isolation-by-distance model is one of the most effective methods for achieving stringent transgene confinement in wheat. The frequency of transgene flow is directly correlated with the relative density of GM pollen grains in air currents, and pollen competition may be a major factor influencing transgene flow.