Incidence of Interspecific Hybrids Resulting from Open Field Pollination of Wild Turnip Populations with Herbicide‐Resistant Rape Pollen

Cultivated rape ( Brassica napus L.) and wild turnip ( Brassica rapa var. oleifera DC) can be readily hybridised by manual hand pollination and represent a crop‐weed combination with high potential for introgression of crop alleles into weed populations. This study investigates the naturally occurring frequency of interspecific hybrids resulting from open field pollination of six wild turnip populations from a range of habitats in New Zealand with herbicide‐resistant rape pollen, over 4 years. When wild turnip and rape plants were established in a 1:1 ratio, the frequency of interspecific hybrid progeny on the wild turnip plants was low (0.06%–2.15%), with no significant differences between the wild turnip populations. The interspecific hybrid frequency was 20‐fold less at a 400:1 ratio of wild turnip and rape plants, also with no significant differences between the wild turnip populations. We conclude that there is a very low risk for wild turnip populations becoming resistant to sulfonylurea herbicides due to allele introgression from sulfonylurea‐resistant forage brassica crops.