Genetic diversity and population structure of leafy kale and Brassica rupestris Raf. in south Italy.

Local varieties of leafy kales (Brassica oleracea L.) are grown in home gardens in Calabria and Sicily for self-consumption, in the same area where the wild relative Brassica rupestris Raf. also grows. With the use of AFLP markers, comparisons were made of the genetic diversity and population structure of ten wild and 22 cultivated populations, as well as of a hybrid population and of four commercial cultivars of different B. oleracea crops. The level of genetic diversity was higher in leafy kales than in wild populations and this diversity was mainly distributed within populations. Wild populations remained distinct from cultivated material. Additionally, most wild populations were distinctively isolated from each other. On the other hand, it was not possible to molecularly distinguish even geographically distant leafy kale populations from each other or from different B. oleracea crops. It was possible to detect inter-crossing between leafy kales and B. rupestris. Findings from this study illustrate the existing level of genetic diversity in the B. oleracea gene pool. Individual populations (either wild or leafy kales) with higher levels of genetic diversity have been identified and suggestions are given for an informed conservation strategy. Domestication hypotheses are also discussed.

Hybridization between oilseed rape (Brassica napus) and different populations and species of Raphanus.

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.