Hybridization rate and fitness of hybrids produced between the tetraploid Camelina rumelica and hexaploid Camelina sativa

Pre-release risk assessment of genetically modified (GM) Camelina sativa (L.) Crantz requires a careful evaluation of the reproductive compatibility with its closely-related Camelina species. Camelina rumelica Velen. is a naturalized weed occurring in C. sativa production region in the northwestern China. In this study, a large number of reciprocal crosses was conducted between the tetraploid C. rumelica and hexaploid C. sativa. The F-1 hybrids were produced by the tetraploid C. rumelica (female) x hexaploid C. sativa (male) at the rate of one hybrid for 217 ovules pollinated, and one hybrid for 220 ovules pollinated in the reciprocal direction. All F-1 hybrids required vernalization treatment to induce timely flowering and showed the significant lower pollen viability (< 2%) compared to the parental lines. Despite that the F-1 failed to backcross with the parental lines, selfed seeds (F-2) were obtained from F-1 hybrids plants. The F-2 hybrids showed some degree of restored pollen viability (about 20%) and successfully produced seeds by both backcrossing and self-pollination. A similar pattern was observed in the field, with F-1 hybrids showing self-compatibility and reduced seed production potential. It is worthwhile to mention that all F-1 and F-2 plants grew well both in the greenhouse and field conditions, but with the significant lower seed production ability. A portion of selfed F-2 seeds from naturally shattering persisted in the soil seedbank during summer period and subsequently germinated in late fall. By contrast, other F-2 seeds may have been dormant in the soil seedbank and germinated the following spring. These altered life-cycle related traits in hybrids generates the novel ecological concerns on the persistence and population dynamics of transient hybrids in the seedbank. In summary, this study provided the evidence that the tetraploid C. rumelica and hexaploid C. sativa, which have the sympatric distributions and overlapped flowering periods, gene flow between them probably could occur. Although the rate was relatively low (about 0.5%), the introgression of life-cycle related traits into C. sativa population could alter its key life-cycle traits and raise the concerns on the soil seedbank persistence and invasiveness of transient hybrid in C. sativa production region in the northwestern China.

Automated summary

The study provides evidence of potential gene flow between tetraploid C. rumelica and hexaploid C. sativa. While F-1 hybrids failed to backcross, selfed seeds (F-2) were obtained, showing restored pollen viability and successful seed production.