A pollen-dispersal experiment with transgenic oilseed rape. Estimation of the average pollen dispersal of an individual plant within a field

In order to help establish a basis for the assessment of gene flow associated with the large-scale release of transgenic oilseed rape, we previously designed a method which makes it possible to retrieve the average pollen dispersal of a single plant from that of a large source plot. The ‘individual’ pollen distribution thus obtained is less dependent on the experimental design than pollen distributions usually published and could therefore be used to model the possible escape of a transgene from commercial transgenic crops. In this study we report on a field experiment set up to study the pollen dispersal from an herbicide-resistant transgenic variety of oilseed rape and to test the applicability of the method on the experimental data. Two techniques were used to determine the individual pollen dispersal, and their outcomes are compared. The results suggest that approximately half of the pollen produced by an individual plant fell within 3 m and that the probability of fertilisation afterwards decreased slowly along a negative exponential of the distance. Comparison with the global pollen distribution from the source plot indicates that pollen-dispersal distributions based on dispersal from whole plots instead of individual plants would have underestimated the proportion of pollen that was dispersed over average or long distances.