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.

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.

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.