Using a zero-inflated model to assess gene flow risk and coexistence of Brassica napus L. and Brassica rapa L. on a field scale in Taiwan.

BACKGROUND: The cropping area of genetically modified (GM) crops has constantly increased since 1996. However, currently, cultivating GM crops is associated with many concerns. Transgenes are transferred to non-GM crops through pollen-mediated gene flow, which causes environmental problems such as superweeds and introgressive hybridization. Rapeseed (Brassica napus L.), which has many GM varieties, is one of the most crucial oil crops in the world. Hybridization between Brassica species occurs spontaneously. B. rapa grows in fields as a weed and is cultivated as a crop for various purposes. Both B. rapa weeds and crops participate in gene flow among rapeseed. Therefore, gene flow risk and the coexistence of these two species should be studied. RESULTS: In this study, field experiments were conducted at two sites for 4 years to evaluate gene flow risk. In addition, zero-inflated models were used to address the problem of excess zero values and data overdispersion. The difference in the number of cross-pollination (CP) events was nonsignificant between upwind and downwind plots. The CP rate decreased as the distance increased. The average CP rates at distances of 0.35 and 12.95 m were 2.78% and 0.028%, respectively. In our results, zero-inflated negative binomial models were comprehensively superior to zero-inflated Poisson models. The models predicted isolation distances of approximately 1.36 and 0.43 m for the 0.9% and 3% threshold labeling levels, respectively. CONCLUSIONS: Cultivating GM crops is prohibited in Taiwan; however, the study results can provide a reference for the assessment of gene flow risk and the coexistence of these two species in Asian countries establishing policies for GM crops.

Model-based calculating tool for pollen-mediated gene flow frequencies in plants.

The potential social-economic and environmental impacts caused by transgene flow from genetically engineered (GE) crops have stimulated worldwide biosafety concerns. To determine transgene flow frequencies resulted from pollination is the first critical step for assessing such impacts, in addition to the determination of transgene expression and fitness in crop-wild hybrid descendants. Two methods are commonly used to estimate pollen-mediated gene flow (PMGF) frequencies: field experimenting and mathematical modeling. Field experiments can provide relatively accurate results but are time/resource consuming. Modeling offers an effective complement for PMGF experimental assessment. However, many published models describe PMGF by mathematical equations and are practically not easy to use. To increase the application of PMGF modeling for the estimation of transgene flow, we established a tool to calculate PMGF frequencies based on a quasi-mechanistic PMGF model for wind-pollination species. This tool includes a calculating program displayed by an easy-operating interface. PMGF frequencies of different plant species can be quickly calculated under different environmental conditions by including a number of biological and wind speed parameters that can be measured in the fields/laboratories or obtained from published data. The tool is freely available in the public domain (http://ecology.fudan.edu.cn/userfiles/cn/files/Tool_Manual.zip). Case studies including rice, wheat, and maize demonstrated similar results between the calculated frequencies based on this tool and those from published PMGF data. This PMGF calculating tool will provide useful information for assessing and monitoring social-economic and environmental impacts caused by transgene flow from GE crops. This tool can also be applied to determine the isolation distances between GE and non-GE crops in a coexistence agro-ecosystem, and to ensure the purity of certified seeds by setting proper isolation distances among field production plots.

Gene flow from transgenic to nontransgenic soybean plants in the Cerrado region of Brazil

Evaluation of transgenic crops under field conditions is a fundamental step for the production of genetically engineered varieties. In order to determine if there is pollen dispersal from transgenic to nontransgenic soybean plants, a field release experiment was conducted in the Cerrado region of Brazil. Nontransgenic plants were cultivated in plots surrounding Roundup Ready transgenic plants carrying the cp4 epsps gene, which confers herbicide tolerance against glyphosate herbicide, and pollen dispersal was evaluated by checking for the dominant gene. The percentage of cross-pollination was calculated as a fraction of herbicide-tolerant and -nontolerant plants. The greatest amount of transgenic pollen dispersion was observed in the first row, located at one meter from the central (transgenic) plot, with a 0.52% average frequency. The frequency of pollen dispersion decreased to 0.12% in row 2, reaching 0% when the plants were up to 10 m distance from the central plot. Under these conditions pollen flow was higher for a short distance. This fact suggests that the management necessary to avoid cross-pollination from transgenic to nontransgenic plants in the seed production fields should be similar to the procedures currently utilized to produce commercial seeds.