Potential for persistence of genes escaped from canola: germination cues in crop, wild, and crop-wild hybrid Brassica rapa

1. Seeds of two wild populations, a crop type (canola) and reciprocal crop-wild hybrids of Brassica rapa were exposed to a factorial combination of light, nutrient and stratification treatments in a growth chamber study to test differences in germination responses to environmental cues. The effects of seed density and nutrient treatment on germination were tested in a separate study. 2. Germination of each type differed in response to treatment combinations. Canola had higher levels of germination than the wild populations. Hybrid germination more closely resembled that of the maternal parent than that of the reciprocal hybrid or paternal parent. Seeds from agricultural and non-agricultural wild populations differed in germination responses to treatments. 3. Testing for viability on ungerminated seeds revealed that mortality differed in response to treatment. Overall, there was low dormancy relative to mortality in the crop, and high dormancy compared to mortality in the wild populations. Levels of dormancy vs mortality in hybrids were intermediate between parents, but more closely resembled the maternal parent. 4. There was no germination response to density for seeds exposed to nutrients. Without nutrients, germination of wild populations responded positively to higher seed densities. 5. The varied germination responses to environmental cues may be the result of different selective pressures on each type. Hybrid cross direction, which affected germination and dormancy, may influence the ability of crop-wild hybrids to persist in natural environments.