| Summary: | Seed losses of oilseed rape (OSR) occur before and during harvest. Seeds can persist in soils for several years and often appear as volunteers in successive crops. Oilseed rape volunteers (OSRV) can harm the product quality if they emerge in subsequent OSR crops differing in fatty acid profile or other quality traits. Several factors can affect volunteer abundance. Important factors identified under controlled conditions are OSR post-harvest management (stubble tillage) and OSR variety selection in terms of the genotypic secondary dormancy potential. In the growing seasons 2009/10 and 2010/11, OSR volunteer abundance was surveyed on agricultural OSR fields in Germany. The main objective was to assess factors affecting volunteer abundance under on-farm conditions by a prediction model. Volunteer numbers were determined by two different approaches: 1. Cultivation of a semi-dwarf hybrid OSR variety, and 2. Survey of OSR volunteers between wide rows in OSR crops. Data analysis taking into account farmers´ questionnaires revealed that the factor “variety selection” was not feasible for the prediction model. As an alternative approach to assess the impact of variety selection on volunteer abundance, the genotypic origin of volunteers was investigated by DNA fingerprints using ISSR (Inter Simple Sequence Repeat)-PCR. Molecular marker analysis confirmed that OSR volunteers were to a large extent identified correctly. In four of seven selected fields, plants could be assigned to open pollinating varieties cultivated previously. In two of these fields, a high dormancy (HD) variety was found to account for a large proportion of the volunteers. In contrast, low dormancy varieties appeared only rarely as volunteers. Hybrid varieties could never be identified, due to genetic segregation in the F2 generation. Taken together, the results indicate that HD varieties substantially contribute to high OSR volunteer abundance in agricultural fields, although more data are needed to confirm this.
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