Polymorphism for interspecific hybridisation within a population of wild radish (Raphanus raphanistrum) pollinated by oilseed rape (Brassica napus)

The within-population polymorphism of wild radish (Raphanus raphanistrum) f or interspecific hybridisation with two cultivars of oilseed rape (Brassica napus) was investigated by hand crossing experiments and fluorescence micr oscopy. Wide variability among plants was observed in the ability of oilsee d rape pollen to germinate on the wild radish stigma; the frequency of pist ils showing pollen tubes ranged from 0 to 1, depending on the female plant. The ratio of fertilised ovules to the total number of ovules in ovaries wh ere pollen tubes arrived ranged from 0.02 to 0.51. Overall, the results pro vide evidence for the presence of different phenotypes. In 40% of the plant s, pistils had no or very few pollen tubes and few fertilised ovules. In 23 %, the foreign pollen tubes grew through the style towards the ovary, but h ad low ovule fertilisation efficiency. The remaining 37% showed a large num ber of pollen tubes in the style and frequent ovule fertilisation, and two plants showed no difference between foreign and conspecific pollen. With re gard to post-zygotic barriers, pollen germination and ovule fertilisation r epresent minor barriers to interspecific hybridisation between oilseed rape and wild radish. It is suggested that the effectiveness of these barriers could be improved through plant breeding; this could reduce the risk of gen e flow from transgenic oilseed rape to populations of wild relatives.