Spontaneous hybridization between oilseed rape (Brassica napus) and weedy B. campestris (Brassicaceae): a risk of growing genetically modified oilseed rape

Frequencies of spontaneous hybridization between oilseed rape (Brassica napus L.) and weedy Brassica campesíris ssp. campestris L. were measured in agricultural fields. Hybrids were identified by enzyme electrophoresis, random amplified polymorphic DNA (RAPD) analysis, chromosome counting, morphology, and pollen fertility. When the two species were mixed 1:1, B. campestris produced 13% hybrid seeds and oilseed rape 9%. In two experiments with single plants of the self-incompatible B. campestris widely spaced within fields of oilseed rape, 56% and 93% hybrid seeds were produced. Analysis of a weedy population of B. campestris in oilseed rape revealed 60% hybrid seeds. Backcrossing of the hybrids to the weedy species seems to occur as supported by the finding in a natural population of two B. campestris-like plants with a marker specific to oilseed rape. The results suggest that transgenes could be dispersed from oilseed rape to B. campestris.