Rosa davidii X virginiana

The F1 hybrid Rosa davidii X virginiana bloomed well for the first time back in early summer, but although some hips looked promising for a while, all but one dropped well before maturity. Here's that lone ripe hip and the only seed it contained (inset). I would have expected this hybrid to be more fertile than this considering that both parent species are tetraploids. I even tried Rosa fedtschenkoana pollen on some flowers and none of those worked either. This year Rosa fedtschenkoana set hips on Rosa davidii itself, so all I can figure is that this F1 is taking after its pollen parent (Rosa virginiana) in being so reluctant to set hips from foreign pollens - and in this case even its own pollen! I wonder who the lucky papa of this lone seed was. Hopefully it'll germinate so I can get some idea.