Fecundity of volunteer oilseed rape and estimation of potential gene dispersal by a practice-related model

Abstract

Abstract Oilseed rape volunteers were able to flower and to set seed in winter wheat and winter barley. The flowering period of the volunteers coincided with the flowering of related wild species which are potential crossing partners, but there was only a short period of synchrony with the flowering period of the sown oilseed rape. Consequently, cross-pollination of volunteers with wild species and sown oilseed rape can potentially occur, even if the number of fertile hybrid offspring is predicted to be small. The number of seeds/volunteer in cereal crops was about 10% of the usual seed number of sown oilseed rape. There were several factors causing this loss, particularly hares which heavily damaged volunteer oilseed rape in cereals. A maximum of 1 GM seed/m2 returned to the soil seed bank from oilseed rape volunteers in winter cereals. The seed productivity of oilseed rape volunteers in sown oilseed rape reached 45% of the sown oilseed rape crop. In a low-risk scenario (low volunteer density, low seed persistence), less than 0.1 GM seed/m2 returned to the soil seed bank. In a high-risk scenario (high volunteer density, high seed persistence), 519 GM seeds set by volunteers would replenish the soil seed bank. As a result of outcrossing an additional 0.4 GM seeds (low-risk: low outcrossing rate, low seed persistence) or 339 GM seeds (high-risk: high outcrossing rate, high seed persistence) set by conventionally bred oilseed rape would also enter the soil seed bank. The EU legislation limit for defining crop seeds as non-GM of 0.9% GM content, would be exceeded in both scenarios, but the low-risk scenario was only shortly beyond the threshold. The number of seeds entering the soil seed bank in high risk-situations can be reduced by measures to reduce seed persistence, such as delayed post-harvest tillage.