Spontaneous hybridization between oilseed rape (Brassica napus) and weedy relatives

Frequencies of spontaneous hybridization between oilseed rape (Brassica napus) and weedy B. campestris (B. rapa) were measured in agricultural fields. The interspecific hybridization was from 9% to 93% depending on the experimental design. Hybrid seed germinated in the field and adult hybrids were observed in the next growing season. The pollen fertility of the hybrids was reduced to 35% on an average, and they produced 102 seeds/hybrid in spontaneous backcrosses with the parental species. The inheritance of 17 oilseed rape specific markers was analyzed in selected backcross plants. The production of spontaneous hybrids was confirmed in field experiments with mixtures of transgenic, herbicide tolerant oilseed rape and B. campestris. The interspecific hybrids were herbicide tolerant and PCR (Polymerase Chain Reaction) confirmed the presence of the transgene construct. The spontaneous backcrossing to B. campestris was likewise confirmed in field experiments with mixed populations of B. campestris and interspecific hybrids with the transgene construct. In the interspecific combination B. juncea x B. napus a frequency of 3% spontaneous hybridization was observed in the field. Our results suggest that transgenes could be dispersed from oilseed rape to related Brassica species.