The low percentage of survivors was mitigated by the initial 21,000 seeds, which should have produced 3,000 zygotic seedlings. .5 % of those gives approximately 15 (actually 12) healthy, vigorous survivors. This winter has been quite mild to this point and unless there's a dramatic change, the number of survivors would have been much higher. I was fortunate to have a severe winter, as it eliminated many less hardy plants.
I am satisfied that last winter's survivors were not a fluke, as the hardiest show no damage this winter.
I believe any Flying dragon seedlings not showing contorted branching should be zygotic, as nucellar seedlings should be all be contorted. Some of the contorted seedlings may also by zygotic.
Unfortunately, I am not aware of any more northerly Poncirus growers. However, although there has been dieback on mature trees on occasion, the last truly deadly winter was in 1994. I'm certain Poncirus can survive further north, but that dieback is likely increasingly severe as one goes north. I'm skeptical of survival in north-central Pennsylvania as well as central New York state. Coastal New Jersey/New York/New England may fare better.
If I'm successful in getting the segentranges to flower and fruit, I would expect a modest to high percentage of their zygotic seedlings to be hardy in zone 6b. I fervently wish I had embarked on this project sooner and more seriously.
Here a 2 photos of Conestoga # 11 segentrange top grafted on Poncirus out of doors. There's no damage on the # 11, but there's minor damage on late growing Poncirus twigs on the rootstock. These scions look very promising at present, but February and March are still remaining on the calendar.