title: Hybridization between oilseed rape (Brassica napus) and different populations and species of Raphanus.
abstract: When cultivating genetically modified varieties, the spontaneous gene flow between crop and wild relatives could be of concern. We analyzed spontaneous hybridization between a transgenic male-sterile line of oilseed rape (Brassica napus, 2n = 38, AACC) and, as pollen donors, three European populations of wild radish (Raphanus raphanistrum, 2n = 18, Rr,Rr) and a variety of cultivated radish (Raphanus sativus, 2n = 18, RR). Seeds showed size and shape dimorphism that correlated to the frequency of hybrids. The offspring were scored morphologically and analyzed using DNA markers (inter-simple sequence repeats) to quantify hybrid frequencies. Seed set ranged from 0.4-1.2 seeds per pod, and 0.02-0.6 seeds per pod were confirmed as hybrids. The frequency of confirmed hybrids differed significantly among populations of R. raphanistrum. In the cross with a French population, all offspring were hybrids; in the cross with a Swiss population, 53% of the offspring were hybrids; and in the cross with a Danish population, only 2% of the offspring were found to be hybrids. The remaining offspring apparently belonged to two groups: the majority was B. napus-like plants, possibly of matromorphic origin, and a minority from the Danish cross seemed to carry fragments of the Raphanus genome. In the cross with a cultivated R. sativus, all offspring were found to be hybrids. This is the first report on spontaneous hybridization between B. napus and R. sativus. Hybrids from all cross-combinations had low pollen fertility (0-15%). If R. raphanistrum occurs where male-sterile B. napus is cultivated, large regional differences in hybridization frequencies between the species could complicate environmental risk assessment of transgenic oilseed rape.
authors.affiliation: Biosystems Department, Risø National Laboratory, 4000 Roskilde, Denmark.
authors.forename: Henriette
authors.initials: H
authors.lastname: Ammitzbøll
authors.forename: Rikke
authors.initials: R
authors.lastname: Bagger Jørgensen
mesh_terms: D029688:Brassica napus / Q000235:genetics*; D003433:Crosses, Genetic; D051456:Gene Flow; D005819:Genetic Markers; D005828:Genetics, Population; D006824:Hybridization, Genetic; D030821:Plants, Genetically Modified / Q000235:genetics*; D011003:Ploidies; D011058:Pollen / Q000235:genetics / Q000502:physiology; D031224:Raphanus / Q000235:genetics*; D018570:Risk Assessment; D012639:Seeds / Q000254:growth & development / Q000502:physiology
chemical_list: D005819:Genetic Markers