Within-population variation in hybridisation and transgene transfer between wild Brassica rapa and Brassica napus in the UK

Several studies in Europe and North America have shown that cultivated Brassica napus will readily hybridise with wild Brassica rapa but at widely different frequencies. To understand the implications of this phenomenon with regard to transgene flow, we examined the rate at which cultivated B. napus cv. Westar containing a capsid (coat protein, CP)-coding sequence from Turnip mosaic virus (Potyvirus) hybridised under glasshouse conditions with wild B. rapa from Culham, in Oxfordshire, UK. We found that the hybridisation rate, as judged using simple sequence repeat (SSR)-PCR and primer oligonucleotides specific for either the C or the A genomes in progeny from individual crosses varied from 5% to 100%. In hybrids (F1 progeny), transgene transfer was always observed (inferred by SSR-PCR) when hybrids were detected. Our observations revealed a hitherto unrecorded source of variability in transgene flow to wild UK B. rapa