Persistence, dispersal and volunteers
Compared with many other crop plants, oilseed rape (Brassica napus L.) has some special characteristics.
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It has retained some of the features of wild plants, which enable it to assert itself outside cultivated fields. Flowering rape plants can often be seen alongside foot paths, railway lines and on the central reservations of motorways.
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Rape seeds can survive in the soil for years. Rape often emerges as volunteer plants in the years following crop rotation. In addition, rape seed pods are not very stable and so many seeds are shed during harvesting.
 Volunteer rape in winter wheat |
Research projects: summary of resultsTopic: The problem of "volunteer" oilseed rape, i.e. the emergence of oilseed rape plants in later crops in the rotation, is sufficiently well-known in farming practice. Oilseed rape volunteers come from rape seeds that remain on the field as crop loss and continue to be viable for years because of their high survival ability. Result (1): Appropriate soil cultivation measures can significantly reduce the potential of volunteer rape. Persistence levels in oilseed rape seeds largely depend on the variety (genotype ). Transgenic and conventional rape varieties with low levels of persistence are already available. Result (2): Heavy seed losses are to be expected when harvesting oilseed rape. By using appropriate soil cultivation, in this case tilling twice (the soil is loosened, but not turned), the proportion of seeds in the soil was reduced by over 99 percent. Result (3): High levels of persistence have been observed in rape seeds. Viable, non-transgenic rape seeds have even been found on release plots which were harvested in 1996. Unfavourable conditions around harvest time can lead to the formation of large seed banks in the soil. Appropriate soil cultivation can minimise oilseed rape volunteers in the following crop. |
 Oilseed rape at a ruderal site |
Topic: Dispersal behaviour: Cultivated oilseed rape has a strong feral potential and is often found growing beside railway lines and on wasteland. Results: Wild cultivated rape can often be seen on ruderal sites along verges and railway lines. Molecular-genetic investigations show that clumps appearing on one site over several years were often the result of new arrivals. A rape seed potential was found only in a few soil samples from ruderal sites. |
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