Sexual hybridization between Capsella bursa-pastoris (L.) Medik (♀) and Camelina sativa (L.) Crantz (♂) (Brassicaceae)

The development of transgenic oilseed Camelina sativa (2n = 40) and the potential for hybridization with its weedy relative Capsella bursa-pastoris (2n = 36) necessitates a careful evaluation of the reproductive compatibility between the species. Here, we conducted over 1800 crosses (emasculation and manual pollination) to examine the ability of 10 Canadian C. bursa-pastoris (♀) accessions to hybridize with five accessions of C. sativa (♂). Seven hybrids were confirmed among 586 putative hybrids screened with species-specific markers, indicating a hybridization rate of 1.5 hybrids per 10 000 ovules pollinated. All seven hybrids had intermediate DNA content compared to their parents, were morphologically distinct, had low (1.9%) pollen fertility and failed to produce selfed or backcrossed seed. Given the abundance of C. bursa-pastoris along field margins, hybrids will likely be generated in the wild, but they will be unable to establish lineages unless fertility is restored. The large number of crosses and the diversity captured by the use of multiple accessions resulted in strong statistical power and a high degree of confidence in the estimated hybridization rate.