Hybridization rate and hybrid fitness for Camelina microcarpa Andrz. ex DC (♀) and Camelina sativa (L.) Crantz(Brassicaceae) (♂)

Hybridization between crops and their wild relatives has the potential to introduce novel variation into wild populations. This novel variation may provide the raw material needed to allow a species to overcome limits to its geographic range. Camelina (Camelina sativa) is a short-season, annual oilseed and cultivars with novel traits are in development, prompting a need to evaluate the potential for transgene introgression into weedy relatives. Little-podded false flax (littlepod; Camelina microcarpa) is a naturalized weed in Canada and the USA, which is an obligate winter annual and requires a longer season for successful seed set. Here we evaluated the sexual hybridization rate between the three cytotypes of littlepod (♀) and camelina (♂), assessed characteristics of hybrids, and evaluated the fitness of hexaploid littlepod and camelina hybrids in the glasshouse and field. In total we conducted, 1,005 manual crosses with diploid littlepod, 1, 172 crosses with tetraploid littlepod, and 896 crosses with hexaploid littlepod. Hybrids were not produced by the diploids, but were produced by the tetraploids and hexaploids at rates of 1 hybrid for 2,000 ovules pollinated and 24 hybrids for 25 ovules pollinated, respectively. Hybrids between tetraploid littlepod and camelina showed low pollen fertility and produced a small number of seeds. In the glasshouse, hybrids between hexaploid littlepod and camelina also showed significantly lower pollen fertility and seed production than parental lines, but their seeds showed high viability. A similar pattern was observed in field trials, with hybrids showing reduced plant weight, seed production and seed weight. However, the seed produced by the hybrids germinates at twice the rate compared to seed produced by hexaploid littlepod when grown in Edmonton, Alberta. This is potentially the result of a shortened life-cycle, a characteristic of camelina. The introduction of the genes controlling these traits into littlepod populations may allow range expansion northward and contribute to the persistence of crop genes. Future work should evaluate the hybridization rate in the field and the role of time to maturity in limiting hexaploid littlepod’s current geographic distribution.