Details

Autor(en) / Beteiligte

• Simpson, Euan C

Titel

The impact of herbicide tolerant oilseed rape in selected agro-ecosystems

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2002

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• A range of field studies of cross pollination between herbicide tolerant and conventional oilseed rape crops and plots were conducted to demonstrate the effects of variety, distance, pollen source and sink size and intervening crop on levels of outcrossing. Experiments investigating the influence of variety on outcrossing showed that hybrid oilseed rape varieties containing high proportions of male sterile plants (varietal associations) were pollinated at higher frequencies than standard fully fertile varieties. Studies conducted using various sizes of genetically modified herbicide tolerant (GMHT) pollen sources showed that small GMHT feral populations cross pollinated with crops in close proximity and the levels of contamination obtained depended on the genotype of the conventional crop. Long range cross pollination of male sterile oilseed rape receptor plots showed that pollination events were measurable at up to 600m from the large GMHT pollen source. Results from a study of cross pollination between mixed populations of GMHT oilseed rape plants and conventional varieties also demonstrated that a hybrid rape type (varietal association) was cross pollinated at considerably higher levels than an open pollinated and a fully restored hybrid variety. Evidence gathered in the experiment suggested that, over a wide range of initial GMHT contamination rates, the final proportion of GMHT seed in the total population was a constant fraction of the initial contamination rate. Outcrossing data was used to compare negative exponential and inverse power law models for their fit to describe the observed relationship between cross pollination and distance from source. Results showed that the inverse power law provided a better fit of the data. This demonstrated that dispersal described by the inverse power law was more likely to lead to cross pollination at both near and large distances from the pollen source compared to the negative exponential model. The consequences of the likely ecological behaviour of GMHT traits resulting from the dispersal curves for regulation and risk assessment are discussed.