A sexual hybrid and autopolyploids detected in seed from crosses between Neslia paniculata and Camelina sativa (Brassicaceae)

Abstract

It is important to understand the probability of hybridization and potential for introgression of transgenic crop alleles into wild populations as part of pre-release risk assessment. Here we completed bidirectional crosses between the emerging crop, camelina [Camelina sativa (L.) Crantz] and its weedy relative, ball mustard [Neslia paniculata (L.) Desv.]. Ball mustard is a self-compatible annual that produces hard ball-like seeds similar to canola or mustard seed in size and shape. A total of 1593 crosses were completed and collected with camelina as the maternal parent, while 3253 crosses were successfully collected in the reverse direction. Putatively hybrid seedlings were screened with flow cytometry and species-specific nuclear ribosomal internal transcribed spacer (ITS) markers. Three plants had DNA contents close to expectations for hybrids, but only one of these, formed on camelina, had the expected ITS markers. This hybrid exhibited low fertility, and neither self-pollination nor backcrossing produced viable progeny. The other two plants, formed on ball mustard, had high pollen and seed fertility and were identified as ball mustard neoautotetraploids. Therefore, the hybridization rate between camelina and ball mustard is relatively low at one in 20 000 ovules pollinated when camelina is the maternal parent. However, autotetraploids may form frequently in ball mustard, and tetraploid populations may exist in nature.