I know what you mean about the whole identity problem when hybridizing garden roses with species. Sometimes it’s very clear that the cross produced the offspring, but sometimes you wonder if any parent pollen germinated at all. I once did several crosses of R. virginiana X Aloha. I was so excited to see the offspring, of which there were many. Most developed successfully into young shrubs, but they all looked just like R. virginiana. My speculation is that each flower was self-pollinated before I got to it. The rapid development of single flowers of species roses may be at the root of it. If any pollen is released from the anthers before emasculation, you can bet on getting copies of the parent species. In the future, I’m going to try to emasculate the flowers gently, but very early in the floral development, hopefully forstalling self-pollination.
I can’t remember, and I skimmed over your replies, but did you mention why you didn’t use R. moyesii as a seed parent? Does R. moyesii not set hips with foreign pollen, or are there some chromosome segregation problems with R. moyesii as a seed parent? It seems to me it would be easier to distinguish successful crosses from any self-pollination, which would yield seedlings that are clearly R. moyesii.
I put pollen from every rose I have on R. moyesii as well as pollen from dozens of other roses from other people and places and never once got a hip from a hybrid cross. Another breeder here has done the same with moyesii with no more success than I had.
Basically it’s statistics. We know that roses make pollen having a range of ploidy levels. We suspect that the ova of roses are also produced on a range of ploidy levels. Statistics favor a pollen grain of moyesii matching the ploidy level of another rose rather than vice-versa because there are very many more pollen granules than ova. Add to ploidy level the need for also being genetically compatible and pollen is even more favored over ova.
It seems to me it would be easier to distinguish successful crosses from any self-pollination,
Not in my experience. To me, successful f1 hybrids look like the species parent so much that I cannot tell a hybrid from a selfling. Actually I share your experience with virginiana. Some breeders are better than I am at distinguishing f1 hybrids and have had spectacular results with subsequent generations. Ralph Moore and Len Scrivins come to mind, you can find their work documented at HMF.
As far as I can make out Moyessi and its Hybrids are difficult to make set hips, Nevada being one of these will not set hips but is very fertile in the pollen department.