Survival of buried seeds of interspecific hybrids between oilseed rape, hoary mustard and wild radish

Two experiments were designed to assess seed survival in the soil of rape (Brassica napus L.), hoary mustard, interspecific hybrids between rape and hoary mustard (Hirschfeldia incana (L.) Lagreze-Fossat) as well as between rape and wild radish (Raphanus raphanistrum L.). The first experiment dealt with seed survival in undisturbed soil over 41 months. It showed a slow decrease in viability of the seeds of hoary mustard, a quick drop to a constant 1% viability of rape, and intermediary behaviour of hybrids. The second experiment was conducted at two held sites in eastern and southern France, with normal cultivation and crop growth during 3 years. Quantitative differences were observed between the two sites, although the relative behaviour of each seed type was similar. Hoary mustard had the greatest seed viability, on average 14% after 3 years, while total seedling emergence in the field was 1.9% after 3 years. The decrease of the viability of rape seed was slower than in the undisturbed experiment, with more than 1% viable seeds remaining after 3 years. Total emergence of rape was up to 4%. Hybrids showed lower seed viability than rape. Total seedling emergence over 3 years was less than 1%. These results are discussed together with the consequences of commercial release of transgenic crops. Transgenes can escape via seeds and volunteer rape, and seeds of interspecific hybrids between rape and wild relatives can survive and germinate after several years, ensuring genetic and spatial spread of transgenes. (C) 1998 Elsevier Science B.V. All rights reserved.